US20170020683A1 - Bone plate stabilization system and method for its use - Google Patents

Abstract

An example device for implantation into a patient at a location between two bone bodies.

Description

RELATED PATENT APPLICATIONS
• This application claims the benefit of priority from and incorporates herein by reference in their entirety all of the several applications identified herein. Specifically, this application claims the benefit of, as a continuation-in-part application of, U.S. patent application Ser. No. 11/735,723 filed Apr. 16, 2007, which in turn claims benefit of, as a non-provisional application of, U.S. Provisional Patent Application No. 60/745,294 filed Apr. 21, 2006, and which also in turn claims benefit of, as a continuation-in-part application of, U.S. patent application Ser. No. 11/620,255 filed Jan. 5, 2007, now U.S. Pat. No. 8,100,976, and, as a continuation-in-part application of, U.S. patent application Ser. No. 11/248,651 filed Oct. 12, 2005, now U.S. Pat. No. 7,985,255, both of which just-identified applications (Ser. Nos. 11/620,255 and 11/248,651) claim benefit of and are continuations-in-part applications of U.S. patent application Ser. No. 10/419,652 filed Apr. 21, 2003, now U.S. Pat. No. 6,984,234, the contents of all of which are incorporated herein by reference in their entirety.
FIELD OF THE INVENTION
• The present invention relates generally to implant devices for the fixation and support of bone bodies. In particular, the present invention relates to an implant device that provides and controls limited movement between bone bodies during fusion, having subsidence control.
BACKGROUND OF THE INVENTION
• The spinal column of vertebrates provides support to bear weight and protection to the delicate spinal cord and spinal nerves. The spinal column comprises a series of vertebrae stacked on top of each other. There are typically seven cervical (neck), twelve thoracic (chest), and five lumbar (low back) segments. Each vertebra has a cylindrical shaped vertebral body in the anterior portion of the spine with an arch of bone to the posterior which covers the neural structures. Between each vertebral body is an intervertebral disk, a cartilaginous cushion to help absorb impact and dampen compressive forces on the spine. To the posterior the laminar arch covers the neural structures of the spinal cord and nerves for protection. At the junction of the arch and anterior vertebral body are articulations to allow movement of the spine.
• Various types of problems can affect the structure and function of the spinal column. These can be based on degenerative conditions of the intervertebral disk or the articulating joints, traumatic disruption of the disk, bone or ligaments supporting the spine, tumor or infection. In addition congenital or acquired deformities can cause abnormal angulation or slippage of the spine. Slippage (spondylolisthesis) anterior of one vertebral body on another can cause compression of the spinal cord or nerves. Patients who suffer from one of more of these conditions often experience extreme and debilitating pain, and can sustain permanent neurologic damage if the conditions are not treated appropriately.
• One technique of treating these disorders is known as surgical arthrodesis of the spine. This can be accomplished by removing the intervertebral disk and replacing it with bone and immobilizing the spine to allow the eventual fusion or growth of the bone across the disk space to connect the adjoining vertebral bodies together. The stabilization of the vertebra to allow fusion is often assisted by a surgically implanted device to hold the vertebral bodies in proper alignment and allow the bone to heal, much like placing a cast on a fractured bone. Such techniques have been effectively used to treat the above described conditions and in most cases are effective at reducing the patient's pain and preventing neurologic loss of function. However, there are disadvantages to the present stabilization devices.
• The spinal fixation device needs to allow partial sharing of the weight of the vertebral bodies across the bone graft site. Bone will not heal if it is stress shielded from all weight bearing. The fixation device needs to allow for this weight sharing along with the micromotion that happens during weight sharing until the fusion is complete, often for a period of three to six months or longer, without breakage. The device must be strong enough to resist collapsing forces or abnormal angulation during the healing of the bone. Loss of alignment during the healing phase can cause a poor outcome for the patient. The device must be secure in its attachment to the spine to prevent migration of the implant or backout of the screws from the bone which could result in damage to the structures surrounding the spine, resulting in severe and potentially life threatening complications. The device must be safely and consistently implanted without damage to the patient.
• Several types of anterior spinal fixation devises are in use currently. One technique involves placement of screws all the way through the vertebral body, called bicortical purchase. The screws are placed through a titanium plate but are not attached to the plate. This device is difficult to place, and over penetration of the screws can result in damage to the spinal cord. The screws can back out of the plate into the surrounding tissues as they do not fix to the plate. Several newer generation devices have used a unicortical purchase of the bone, and in some fashion locking the screw to the plate to provide stability and secure the screw from backout. Problems have resulted from over ridged fixation and stress shielding, resulting in nonunion of the bony fusion, chronic micromotion during healing resulting in stress fracture of the fixation device at either the screw or the plate, insecure locking of the screw to the plate resulting in screw backout, or inadequate fixation strength and resultant collapse of the graft and angulation of the spine.
• These devices are often designed to support and bridge across a group of vertebrae, for example a group of three. Because these devices are typically bridged across the bone, for example in the cervical region, they occasionally aggravate the esophagus, making it difficult for one to swallow food. In addition, the screws are installed into the bone normal, i.e., 90° to the plate's surface. Local angularity in the vertebral column often causes high shearing stresses to be applied to the screws. These stresses may fatigue the screws or cause deformation of the screw holes.
• Thus, there is a need for a device and method of supporting adjacent vertebrae that avoids these problems and risks to the patient.
• Bone mechanical properties greatly influence the stiffness of vertebra-implant-vertebra constructs. Bone properties are a function of many factors including bone mineral density, age, and sex. For comparative purposes, it will be assumed that bone properties are constant in the following discussions. Preparation of the bone to receive the implant can influence strength and stiffness. Again, for comparative purposes, it will be assumed that bone preparation is not a variable except when specifically discussed.
• Interbody devices are typically classified as threaded cylinders or screws (e.g., BAK C), boxes (usually tapered rectangular boxes with ridges like the Brantigan cage), or vertical cylinders (e.g., Harms cage). Threaded cylinders usually have small pores and graft material is located inside the hollow interior of the cylinder. Device stiffness might be an issue for such designs. Boxes and vertical cylinders are generally open structures and in these devices a combination of device stiffness and subsidence are responsible for loading the graft.
• The stiffness of a material and the stiffness of the structure (device) are often confused. Material stiffness is quantified by Modulus of Elasticity, the slope of the stress-strain curve. Steel has a high modulus, and gold has a low modulus. Structural or device stiffness is a function of dimensions of the part and the material from which the part is made. For example, steel is a very stiff material. However, when formed into the shape of a structure like a paperclip it is easily bent. Stiffness of an assembly or construct can be influenced by connections. While a paperclip and even a piece of paper are strong in tension, when assembled with a piece of paper a paperclip can be easily pulled off because they are only held together by friction.
• The same analogy holds for inter-vertebral implants. For instance, consider a simplified construct consisting of a bone block, an interbody device, and a bone block, stacked on top of each other and loaded in compression. If the device is made from a low modulus material but has a large footprint on the bone, and conforms very well to the bone, the assembly can be very stiff in compression. The slope of the load-deflection curve would be steep. A device made from a high modulus material that has a small footprint on the bone and sharp edges might simply punch into the bone under compressive load. The slope of the load-deflection curve would be low, making the construct appear very compliant despite the fact that the device is rigid.
• The terms flexibility and stiffness are used in connection with both the range of motion of the spine and the mechanical performance of implant constructs, and the distinction is not always clearly defined.
• The spinal column of vertebrates provides support to bear weight and protection to the delicate spinal cord and spinal nerves. The spinal column includes a series of vertebrae stacked on top of each other. There are typically seven cervical (neck), twelve thoracic (chest), and five lumbar (low back) segments. Each vertebra has a cylindrical shaped vertebral body in the anterior portion of the spine with an arch of bone to the posterior, which covers the neural structures. Between each vertebral body is an intervertebral disc, a cartilaginous cushion to help absorb impact and dampen compressive forces on the spine. To the posterior the laminar arch covers the neural structures of the spinal cord and nerves for protection. At the junction of the arch and posterior vertebral body are articulations to allow movement of the spine.
• Various types of problems can affect the structure and function of the spinal column. These can be based on degenerative conditions of the intervertebral disc or the articulating joints, traumatic disruption of the disc, bone or ligaments supporting the spine, tumor or infection. In addition congenital or acquired deformities can cause abnormal angulation or slippage of the spine. Slippage (spondylolisthesis) anterior of one vertebral body on another can cause compression of the spinal cord or nerves. Patients who suffer from one of more of these conditions often experience extreme and debilitating pain, and can sustain permanent neurological damage if the conditions are not treated appropriately.
• One technique of treating these disorders is known as surgical arthrodesis of the spine. This can be accomplished by removing the intervertebral disc and replacing it with bone and immobilizing the spine to allow the eventual fusion or growth of the bone material across the disc space to connect the adjoining vertebral bodies together. The stabilization of the vertebra to allow fusion is often assisted by a surgically implanted device to hold the vertebral bodies in proper alignment and allow the bone to heal, much like placing a cast on a fractured bone. Such techniques have been effectively used to treat the above-described conditions and in most cases are effective at reducing the patient's pain and preventing neurological loss of function. However, there are disadvantages to the present stabilization devices.
• Several types of anterior spinal fixation devices are in use currently. One technique involves placement of screws all the way through the vertebral body, called bicortical purchase. The screws are placed through a titanium plate but are not attached to the plate. This device is difficult to place, and over penetration of the screws can result in damage to the spinal cord. The screws can back out of the plate into the surrounding tissues, as they do not fix to the plate. Several newer generation devices have used a unicortical purchase of the bone, and in some fashion locking the screw to the plate to provide stability and secure the screw from back out. Problems have resulted from over rigid fixation and stress shielding, resulting in nonunion of the bony fusion, chronic micromotion during healing resulting in stress fracture of the fixation device at either the screw or the plate, insecure locking of the screw to the plate resulting in screw back out, or inadequate fixation strength and resultant collapse of the graft and angulation of the spine.
• These devices are often designed to support and bridge across a group of vertebrae, for example a group of three. Because these devices are typically bridged across the bone, for example in the cervical region, they occasionally aggravate the esophagus, making it difficult for one to swallow food. In addition, the screws are installed into the bone normal, i.e., 90° to the plate's surface. Local angularity in the vertebral column often causes high shearing stresses to be applied to the screws. These stresses may fatigue the screws or cause deformation of the screw holes.
BRIEF SUMMARY OF THE INVENTION
• The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
• In accordance with an aspect of the present invention, at least one implant device is provided.
• The following description and the annexed drawings set forth in detail certain illustrative aspects of the invention. These aspects are indicative, however, of but a few of the various ways in which the principles of the invention may be employed and the present invention is intended to include all such aspects and their equivalents. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
• The foregoing and other features and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings.
• FIG. 1 is a perspective view of a bone stabilization plate system according to the invention that is assembled between adjacent vertebrae.
• FIG. 2 is a perspective view of the bone stabilization plate system ofFIG. 1.
• FIG. 3 is a side cross-sectional view of the bone stabilization plate system ofFIG. 1 assembled between adjacent vertebrae.
• FIG. 4 is a top view of the bone stabilization plate system ofFIG. 1.
• FIG. 5 is a side view of a bone screw for use in the bone stabilization plate system depicted inFIGS. 1 to 4.
• FIG. 6 is a perspective view of a retaining plate for use in the bone stabilization plate system depicted inFIGS. 1 to 4.
• FIG. 7 is a top view of the retaining plate ofFIG. 6.
• FIG. 8 is a front perspective view of an interbody device in accordance with an aspect of the present invention.
• FIG. 9 is a bottom perspective view of an interbody device in accordance with an aspect of the present invention.
• FIG. 10 is a side view of an interbody device in accordance with an aspect of the present invention.
• FIG. 11 is a front perspective view of a base member of an interbody device in accordance with an aspect of the present invention.
• FIG. 12 is a back perspective view of a base member of an interbody device in accordance with an aspect of the present invention.
• FIG. 13 is a side view of a base member of an interbody device in accordance with an aspect of the present invention.
• FIG. 14 is a bottom perspective view of a base member of an interbody device in accordance with an aspect of the present invention.
• FIG. 15 is a perspective view of a bone screw of an interbody device in accordance with an aspect of the present invention.
• FIG. 16 is a front perspective view of a restraining member of an interbody device in accordance with an aspect of the present invention.
• FIG. 17 is a back perspective view of a restraining member of an interbody device in accordance with an aspect of the present invention.
• FIG. 18 is a side perspective view of an interbody device positioned between two bone bodies in accordance with an aspect of the present invention.
• FIG. 19 is a top perspective view of an interbody device positioned between two bone bodies in accordance with an aspect of the present invention.
• FIG. 20 is a perspective view of a guide tube system for inserting bone screws into a base member of an interbody device in accordance with an aspect of the present invention.
• FIG. 21 is a bottom perspective view of another guide tube system for inserting a bone screw into a base member of an interbody device in accordance with an aspect of the present invention.
• FIG. 22 is a side perspective view of another interbody device in accordance with an aspect of the present invention.
• FIG. 23 is a back perspective view of another base member of an interbody device in accordance with an aspect of the present invention.
• FIG. 24 is a back perspective view of a base member of an interbody device in accordance with an aspect of the present invention.
• FIG. 25 is a back perspective view of a base member of an interbody device in accordance with an aspect of the present invention.
• FIG. 26 is a side view of a base member of an interbody device in accordance with an aspect of the present invention.
• FIG. 27 is a back perspective view of a base member of an interbody device in accordance with an aspect of the present invention.
• FIG. 28 is a back perspective view of a base member of an interbody device in accordance with an aspect of the present invention.
• FIG. 29 is a back perspective view of a base member of an interbody device in accordance with an aspect of the present invention.
• FIG. 30 is a front perspective view of an interbody device in accordance with an aspect of the present invention.
• FIG. 31 is a side perspective view of another interbody device in accordance with an aspect of the present invention.
• FIG. 32 is an angled front perspective view of an implant device including a base member having a peripherally-surrounded chamber in accordance with an aspect of the present invention.
• FIG. 33 is a side view of an implant device in accordance with an aspect of the present invention.
• FIG. 34 is an angled front perspective view of a base member of an implant device including a peripherally-surrounded, multiple-compartment chamber in accordance with an aspect of the present invention.
• FIG. 35 is an angled front perspective view of a base member of an implant device including a peripherally-surrounded, chamber in the unassembled position in accordance with an aspect of the present invention.
• FIG. 36 is an angled front perspective view of a base member of an implant device including a laterally-enclosable, multiple-compartment chamber in an unassembled position in accordance with an aspect of the present invention.
• FIG. 37 is an angled front perspective view of a base member of an implant device including a laterally-enclosable chamber in the unassembled position in accordance with an aspect of the present invention.
• FIG. 38 is an angled front perspective view of a base member of an implant device including a laterally-enclosable, multiple-compartment chamber in an unassembled position in accordance with an aspect of the present invention.
• FIG. 39 is a front perspective view of a base member of an implant device including a peripherally-surrounded chamber in accordance with an aspect of the present invention.
• FIG. 40 is a front perspective view of a base member of an implant device illustrating possible modifications to the above-identified embodiments in accordance with an aspect of the present invention.
• FIG. 41 is partially broken away rear perspective view of a base member of an implant device illustrating possible modifications to the above-identified embodiments in accordance with an aspect of the present invention.
• FIG. 42 is partially broken away rear perspective view of a base member of an implant device illustrating possible modifications to the above-identified embodiments in accordance with an aspect of the present invention.
• FIG. 43 is partially broken away rear perspective view of a base member of an implant device illustrating possible modifications to the above-identified embodiments in accordance with an aspect of the present invention.
• FIG. 44 is partially broken away rear perspective view of a base member of an implant device illustrating possible modifications to the above-identified embodiments in accordance with an aspect of the present invention.
DESCRIPTION OF EXAMPLE EMBODIMENTS
• The present invention relates to a device, such as an implant device that provides and controls limited movement between bone bodies during fusion. The present invention will now be described with reference to the drawings, wherein like reference numerals are used to refer to similar elements throughout. It is to be appreciated that the various drawings are not necessarily drawn to scale from one figure to another nor inside a given figure, and in particular that the size of the components are arbitrarily drawn for facilitating the understanding of the drawings. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It may be evident, however, that the present invention can be practiced without these specific details. Additionally, other embodiments of the invention are possible and the invention is capable of being practiced and carried out in ways other than as described. The terminology and phraseology used in describing the invention is employed for the purpose of promoting an understanding of the invention and should not be taken as limiting.
• While some embodiments of the present invention are described for supporting adjacent cervical vertebrae in the anterior region of the vertebrae, persons skilled in the art would recognize that the bone plate of the present invention may be utilized to support adjoining thoracic and lumbar vertebrae in the lateral or posterior regions of the vertebrae. Further, the device and method of the invention is not limited to vertebral bodies, but can also be used to join two other pieces of bone in other parts of the body.
• Some aspects provide a bone stabilization plate system for stabilizing two adjacent bones (including bone fragments), such as adjacent vertebral bodies, while they heal, as well as to methods for its use. A useful bonestabilization plate system10 constructed in accordance with the present invention is shown inFIGS. 1 to 4. The depicted bone stabilization plate system comprises abase plate20 having first and second ends, and including aprimary member21 and asecondary member22 at the second end of the base plate. Thesecondary member22 is angled relative to theprimary member21, as discussed further below, although other designs are contemplated within the scope of the invention.
• Thebase plate20 may be made of any suitable material, and can be made from titanium or a titanium alloy. The thickness of thebase plate20 is not critical, and can range from about 1 mm to about 2 mm, and more specifically is about 1.6 mm. The thickness of thebase plate20 will depend on the particular application.
• FIGS. 1 and 3 show thebase plate20 mounted to first and second adjacentvertebral bodies14 and16 with abone graft12 between the vertebral bodies. Thebase plate20 has abottom surface26 that contacts thebone graft12. The bottom surface is therefore can be generally flat, but can have any other design that permits it to sit against the bone graft is suitable for use in the invention. In the depicted embodiment, thebottom surface26 of thebase plate20 is the bottom surface of theprimary member21. The primary member includes atop surface28 that is opposite thebottom surface26 and aside wall32 at the first end of thebase plate20 that joins the top and bottom surfaces and contacts the firstvertebral bodies14. Thetop surface28 can have any suitable design so that it can receive one or more bone screws and perform as described further below.
• Thesecondary member22 has afront surface30 that is generally continuous with thetop surface28 of theprimary member21 and aback surface31 that is generally continuous with thebottom surface26 of the primary member. Theprimary member21 andsecondary member22 are arranged relative to each other so that their top surfaces form an angle α that is greater than 90° and less than 180°, specifically from 110° to about 160°. As will become apparent, the angle at which the primary and secondary members are joined is provided so that bone screws can be introduced through the base plate at desired angles, as discussed further below. Accordingly, thebase plate20 can be designed in any other manner that permits the bone screws to be introduced therethrough at the desired angles.
• Theprimary member21 includes at least one, and possibly two (as shown in the depicted embodiment) first bone screw holes42 extending therethrough for receiving a corresponding number of first bone screws24. The bone screw holes42 in theprimary member21 are angled relative to thebottom surface26 of the base plate and primary member so that a first bone screw extending through first a bone screw hole extends through the base plate at an angle relative to the bottom surface, for example, through the corner joining thebottom surface26 to theside wall32, as best shown inFIG. 4. As a result, the eachfirst bone screw24 extends into the firstvertebral body14 at an angle, as discussed further below. In the depicted embodiment, each firstbone screw hole42 has a generally conical shape to receive the “radiused” shape of the bottom of the head of the correspondingfirst bone screw24, described further below, but can have any other suitable shape depending upon the shape of the bone screws to be used.
• Thesecondary member22 includes a bone screw hole in the form of an elongatedbone screw slot48 for receiving asecond bone screw25. Thesecond bone screw25 is introduced into thebone screw slot48 and into the secondvertebral body16. Thebone screw slot48 is designed so that thesecond bone screw25 can slide within the slot relative to thebase plate20 generally toward thefirst member21. Thus, in use, as the twovertebral bodies14 and16 to which thebase plate20 is fixed collapse or settle and move toward each other, thesecond bone screw25 contained within thebone screw slot48 will slide within the slot and move with the secondvertebral body16 into which it extends in a direction toward theprimary member21 and the firstvertebral body14.
• The bone screws24 and25 can be made of any suitable material, and can be made of the same material as thebase plate20, such as titanium or a titanium alloy. The bone screws24 and25 can all have the same shape, such as that shown inFIG. 5. In the depicted embodiment, the bone screws24 and25 each have a radiusedhead27. As used herein, the term “radiused head” means that the lower portion of the bone screw head, i.e., the portion that is nearest the shank, is generally rounded, to thereby permit the bone screws to toggle within their respective holes and slot. The bone screws24 and25 can have any other suitable shape that permits them to cooperate with the bone screw holes42 and thebone screw slot48.
• Thesystem10 is designed so that the bone screws24 and25 are introduced into thevertebral bodies14 and15 at an angle other than 90° relative to the bone surface. In one case, the first bone screws24 are introduced into the firstvertebral body14 so that the axis of each bone screw is at an angle relative to the bone surface ranging from about 20° to about 60°, more specifically from about 40° to about 50°. Thesecond bone screw25 can be introduced into the secondvertebral body16 so that the axis of the bone screw is at an angle relative to the bone surface ranging from about 20° to about 70°, more specifically from about 45° to about 65°.
• The bone stabilization plate system includes a bone screw retaining means, which is any means for securedly covering at least a part of each of the bone screws24 and25 so that the bone screws cannot back out from the bone once screwed in through thebase plate20. In the depicted embodiment, the bone screw retaining means comprises a retainingplate50 and a retaining plate fixing means.
• As best shown inFIGS. 6 and 7, the retainingplate50 is a generally flat plate having afirst end51, asecond end52, atop surface53 and abottom surface54 that is shaped to sit against thetop surface28 of thebase plate20. In the depicted embodiment, the retainingplate50 sits in a recessed region of thebase plate20, as best shown inFIG. 3. The use of a recessed region permits the user to more easily properly place the retaining plate on the base plate. The thickness of the retainingplate50 is not critical, but can be ranges from about 0.5 mm to about 2 mm, more specifically from about 1 mm to about 1.5 mm.
• The retainingplate50 includes at itsfirst end51 two generally-roundednotches55 on the sides of itsbottom surface54. When the retainingplate50 is fixed in place over thebase plate20, the two generally-roundednotches55 each cover a portion of a corresponding one of the first bone screws24. The generally-rounded nature of thenotches55 permits the first bone screws24 to toggle within the first bone screw holes42.
• The retaining plate includes at its second end52 aU-shaped notch56, which, in the depicted embodiment, is centered at the edge of the second end. TheU-shaped notch56 includes a generally U-shaped sidewall between the top and bottom surfaces of the retaining plate that is curved outwardly from thetop surface53 to thebottom surface54 so that the opening formed by the notch is larger at the bottom surface of the retaining plate and smaller at the top surface of the retaining plate. When the retainingplate50 is fixed in place over thebase plate20, the top of thesecond bone screw25 sits within theU-shaped notch56 with the top of the second bone screw covered by thetop surface53 of the retaining plate. With this design, thesecond bone screw25 is permitted to slide and toggle within thebone screw slot48 even when the retainingplate50 is fixed over the second bone screw.
• The retainingplate50 also includes aset screw aperture57 between its first and second ends. Theset screw aperture57 in the retainingplate50 is aligned with a set screw aperture (not shown) in thebase plate20, both of which can receive a set screw (not shown) for fixing the retaining plate in place over the base plate. The set screw can be made of any suitable material well known in the art, and can be titanium or a titanium alloy. In one embodiment, the set screw is an hexagonal set screw that can be turned with an hexagonal driver. Other types of set screws can also be used, as well as any other suitable mechanism for fixing the retaining plate to the base plate. The precise mechanism by which the retaining plate is fixed to the base plate is not critical to the invention.
• Any other suitable bone screw retaining means can be used in connection with the invention. For example, the bone screw retaining means can comprise multiple retaining plates that cover different bone screws. Alternatively, the bone screw retaining means can comprise one or more screws with heads that overlap at least a portion of one or more bone screws to thereby prevent the bone screws from backing out. The precise mechanism by which the bone screws are covered is not critical to the invention.
• In the depicted embodiment, thebase plate20 further includes a pair oflateral tabs60 integrally formed with theprimary member21 and extending outwardly from opposite ends of thebottom surface26 of the primary member to form, together with the primary member, a unitary substantially U-shaped structure. In use, thelateral tabs60 extend around thebone graft12 to prevent lateral shift of the graft and control subsidence of adjacent vertebrae as they set during healing. Thelateral tabs60 may be made of any suitable material, and can be made of the same material as thebase plate20. Eachtab60 includes a generally-pointednub66 that extends outwardly from its corresponding tab. The function of thenubs66 is described further below.
• In use, thebase plate20 is placed directly on thebone graft12 such that thebottom surface26 contacts the bone graft and theside wall32 engages aside70 of the firstvertebral body14, as shown inFIGS. 1 and 3. Thesecondary member22 engages a corner or thelip osteophite74 of the secondvertebral body16. Two first bone screws24 are inserted into the first bone screw holes42 in thebase plate20 to anchor the base plate to the firstvertebral body14. The first bone screws24 received by the first bone screw holes42 penetrate thevertebral body14 in an angled alignment. The axial angle of the first bone screw holes42 determines the angle at which the first bone screws24 will be introduced through the firstvertebral body14.
• Thesecondary member22 is secured to the secondvertebral body16 by thesecond bone screw25 being received through thebone screw slot48. Thesecond bone screw25 received by thebone screw slot48 penetrates the secondvertebral body16 through thelip osteophite74. It is possible to anchor thebase plate20 to thevertebral body16 through the lip osteophite because the lip osteophite is structurally the strongest part of the bone. The angle of thesecondary member22 relative to theprimary member21 and the angle through which thebone screw slot48 extends through the second member determine the angle at which thesecond bone screw25 will be inserted in the secondvertebral body16.
• To provide an enhanced fit, a few millimeters of bone can be trimmed or otherwise removed from thelip osteophite74 of the secondvertebral body16 at an angle corresponding to the angle of thesecondary member22. The trimmed surface provides a substantially flat surface for anchoring thesecond bone screw25 into thelip osteophite74 of the secondvertebral body16.
• The angles of the bone screws24 and25 relative to the bone surfaces of thevertebral bodies14 and16 are particularly important. As note above, the lip osteophite is the strongest part of the bone, and thus angling the bone screws through the lip osteophite increases the ability of thebase plate20 to stay anchored to the vertebral bodies. Moreover, by being angled, eachbone screw24 or25 is positioned along the angle of rotation of the corresponding vertebral body as well as the angle of settling of the vertebral body. This places each screw in a protected position against motion of the spinal column. As a result, significant sheer forces are not exerted on the screws as the vertebral bodies rotate and settle.
• As is generally known in the art, a drilling tool may be used to drill holes in the bone to “tap” or prep the bone for receiving the bone screws24 and25. If desired before drilling, a tack tool, a tool having an elongated stem and a removable sharp tack at its distal end, may be used to create a starter hole in the bone to facilitate drilling. After drilling, a tapping tool may be used to tap the drilled holes. Following tapping, the bone screws24 and25 are screwed into the drilled and tapped holes through the bone screw holes42 and thebone screw slot48 of thebase plate20.
• Once the bone screws24 and25 are inserted into the bone screw holes42 and thebone screw slot48, the retainingplate50 is placed over the base plate and fixed in place to prevent the screws from “backing out” of the screw holes. Thesecond bone screw25 that extends through thebone screw slot48 is nonetheless permitted to slide along the length of the slot, even when the retainingplate50 is secured in place. Thus, second thebone screw25 and thebone screw slot48 cooperate to control any lateral or rotary movement of one vertebral body relative to an adjacent vertebral body during “settling” of the bone. Further, the angled orientation of thesecond member22 provides thebase plate20 with resilient properties, for example, enabling the base plate “flex” when one vertebrae is rotated relative to an adjacent vertebrae.
• As noted above, all of the bone screws24 and25 are possibly permitted to toggle, or pivot, even after the retainingplate50 is fixed over thebase plate50. The ability of the screws to toggle permits thesystem10 to migrate and self-center after it has been implanted.
• If thebase plate20 includeslateral tabs60 withnubs66, the nubs will also share in the weight-bearing during settling of the vertebral bodies. Specifically, as the vertebral bodies move toward each other during settling, the pointednubs66 will contact and slowly enter the secondvertebral body16 to a limited extent. This contact can help in controlling the rate of settling.
• In the alternative, relatively smaller (shorter and/or smaller in diameter) bone screws may be used. Because the bone screws penetrate the lip osteophite, which is structurally the strongest portion of the bone, shorter bone screws may be used to anchor the base plate to the bone. Moreover, because the screws are positioned along the angle of rotation of the corresponding vertebral body as well as the angle of settling of the vertebral body, as discussed above, significant sheer forces are not exerted on the screws as the vertebral bodies rotate and settle, thereby minimizing the diameter of screw needed.
• The present invention provides an additional benefit of providing a vertebral support device having a “low profile.” Namely, the base plate of the present invention is specially designed to have an outer periphery that coincides with or generally matches the outer diameter of the cortex. The top surface of the base sits at, and possibly below, the top surface of the vertebral bodies. As such, the bone plate system of the present invention does not have any parts that would significantly interfere with or irritate the trachea, esophagus, and/or other sensory nerves of the user.
• Another advantage of the present bone plate system is that it is stackable. Frequently after a bone graft is inserted and a bone plate joined to the surrounding vertebral bodies, for example, C4 and C5, an adjacent disk, for example, between C5 and C6, subsequently deteriorates. With traditional bone plates, it would be necessary to remove the plate from C5 before attaching a second bone plate to C5 and C6 because each plate covers a significant surface of the vertebral body. To remove a bone plate, it is necessary cut through scar tissue, which can have a negative impact on the patient. In contrast, the bone plate systems of the present invention cover an insignificant portion of the top surfaces of the vertebral bodies to which it is attached, instead being located primarily between the vertebral bodies. As a result, multiple bone plate systems can be introduced over adjacent bone grafts (i.e., between a common vertebral body) so that two bone plate systems are attached to a common vertebral body without the bone plate systems contacting one another. Thus, subsequent procedures where new bone grafts are to be inserted do not require the removal of a pre-existing bone plate prior to introduction of a new bone plate. The depicted systems where the bone screws are provided in a generally triangular arrangement further enhances the stacking ability of the bone plate systems of the invention.
• It is presently considered to provide a kit having base plates of different sizes, bone screws of differing lengths and retaining plates complementary to the base plates. The kit may further comprise a tack tool, a drilling tool, tapping tool and/or one or more screw driving tools.
• Referring toFIGS. 8-10, an example of aninterbody device110 is illustrated in accordance with an aspect of the present invention. Theinterbody device110 is configured to fix and secure two bone bodies. As used herein, the phrase “bone bodies” is intended to include individual bones as well as fragments or portions of bones. More specifically, and as will be described in further detail below, the interbody device can fix and secure adjacent vertebrae that have had cartilaginous disc between the vertebrae replaced with a graft of bone tissue or some other material that promotes the fusion of the vertebrae. It is to be appreciated that one aspect that is addressed by the present invention is load sharing with a graft. The configuration of theinterbody device110 includes abase member120 having a plurality of protrusions orinterface members130 extending from a portion of thebase member120. As will be explained in further detail below, theinterface members130 are configured to contact at least one surface of at least one bone body to provide subsidence control for theinterbody device110. Controlled subsidence relates to resistance to subsidence and total amount of subsidence. Thebase member120 of theinterbody device110 also includes a plurality of apertures, each of which is configured to receive acorresponding bone fastener150 therethrough.
• Theinterbody device110 also includes a restraining means for restricting movement of one ormore bone fasteners150 coupled to thebase member120. The restraining means can be any means for securely covering at least a part of each of thebone fasteners150 so that thebone fasteners150 cannot back out from the bone bodies once screwed in through thebase member120 of thedevice110. In the depicted embodiment, the bone screw restraining means comprises a restrainingplate160 and a restraining plate fixing means170.
• Turning now toFIGS. 11-14, thebase member120 of theinterbody device110 is illustrated in greater detail. Thebase member120 is generally u-shaped with afirst end180 at the open end of the u-shape and asecond end190 at the closed end of the u-shape (seeFIGS. 13 and 14). Thesecond end190 includes aprimary member200 and asecondary member210, which extends from and is angled relative to theprimary member200. First andsecond legs220,230 of theu-shaped base member120 are integrally formed with theprimary member200. In use, the first andsecond legs220,230 extend around a bone graft to mitigate lateral shift of the graft and control subsidence of adjacent vertebrae as they set during fusion.
• Subsidence is further controlled by the presence of theinterface members130 that extend from a portion of thebase member120. Theinterface members130, as depicted in the present embodiment, can include a plurality of teeth extending from bottom surfaces of theprimary member200, thefirst leg220, and thesecond leg230. Accordingly, when coupled with the bone bodies, theinterface members130 extend from thebase member120 in a direction that is aligned with an elongate direction of the spine. Theinterface members130 thus, are configured to provide a progressive penetration into the bone body over a period of time in a direction aligned with the elongate direction of the spine. It is to be appreciated, however, that any suitable configuration of interface members can be provided at any suitable location on the base member that interfaces with a surface of the bone body.
• The interface members can include teeth, knife-edges, spikes, posts, pegs, and the like, including any combination thereof. The configuration of the interface members includes interlocking external features that impact a subsidence profile, which is a relationship between an applied load and an amount of settling theinterbody device110 experiences when secured to the bone bodies. Or in other words, the subsidence profile is a relationship between a depth of subsidence of the interface members and a force required to achieve the depth of subsidence. When first implanted, theinterface members130 will rest on top of the bone surface. When load is applied to theinterbody device110, theinterface members130 will penetrate, or subside, into the bone in a controlled manner. The interface members can readily dig into the bone initially and then slow down as more of the tooth cross section embeds. Different interface member configurations provide different controlled subsidence profiles. The density of the bone body also impacts the subsidence profile. For example, in a lower density bone body representation, such as 15 pcf foam, the interface members can penetrate the bone body by about 1 mm using between about 50-100 N of force and by about 2 mm using between about 150-250 N of force. In a medium density bone body, such as 20 pcf, the interface members can penetrate the bone body by about 1 mm using between about 100-200 N of force and by about 2 mm using between about 400-900 N of force. In a higher density bone body, such as 40 pcf, the interface members can penetrate the bone body by about 1 mm using between about 100-500 N of force and by about 2 mm using between about 1000-2250 N of force. The amount of force needed for displacement and the rate of penetration of the interface members into the bone body depends, in part, upon the configuration of the interface members. It should be noted that all of the pcf densities refer to polyurethane foam (which is referenced to ASTM standards) that is used as a bone analog for test purposes. The tests were also conducted using a straight test “blade” that was 40 mm long, not an actual implant.
• The height (H) of theinterface members130 determines a depth of penetration into the bone body (seeFIG. 11). Generally, when theinterbody device110 has subsided to a point where the interface members are fully embedded in the bone, the applied load will be distributed across the entire surface of theinterbody device110 and subsidence resistance will greatly increase. Typically, the screw will be at the end of the slot. Thus, the height (H) of the interface members can control an amount of subsidence that theinterbody device110 will permit. Theinterface members130 can be of any height or combination of heights. Thus, if a plurality ofinterface members130 extend from a surface of the base member, eachinterface member130 can be of equal heights or substantially taller or shorter than other interface members.FIG. 26, as described in more detail below, illustrates that theinterface members130,132 can extend from the top or bottom surfaces of the base member. Theinterface members130,132 can be of equal height or substantially dissimilar heights depending on the amount of subsidence resistance that is desired.
• In addition to the height (H) of theinterface members130, the shape of theinterface members130 also affects subsidence of theinterbody device110. The shape of theinterface members130 controls a shape of the subsidence profile; and therefore, affects the load shared with the graft material. For instance, if theinterface members130 were limited to a few sharply pointed spikes, subsidence would occur substantially immediately and theinterbody device110 would rapidly seat in the bone to the fullest extent under low force. In this instance, any graft material would be immediately and highly loaded. Such immediate subsidence is not desirable because the joint space could narrow and cause nerve root or spinal cord compression. Also, the graft would be overloaded, inhibiting fusion. However, some subsidence is needed to load the graft and ensure fusion. Accordingly, by configuring theinterface members130 to have a broadly shaped portion, theinterbody device110 has increased resistance to subsidence as theinterface members130 penetrate into the bone body; and the graft material is gradually loaded as the device subsides. For instance, turning toFIG. 14, eachtooth130 is shaped with a substantially broad base, the base being defined by a length (L) and width (W) of each tooth. The substantially broad base of each tooth facilitates controlled subsidence of theinterbody device110. For instance, the as the tooth becomes wider in cross section, the penetration of the tooth into the bone body will become slower.
• Once theinterface members130 have fully penetrated the bone, the surface area of thebase member120 is of an area large enough to resist further subsidence of theinterbody device110. To increase subsidence resistance, at an interface between the a plurality ofteeth130 and the bottom surfaces of theprimary member200 and the first andsecond legs220,230, a shelf-like area235 is created. The shelf-like area235 provides an extended surface area to contact the bone material, thereby increasing subsidence resistance once theinterface members130 have fully subsided. As mentioned, the screw will typically be at the end of the slot.
• Turning back to the primary andsecondary members200,210 of thebase member120, thesecondary member210 has a front surface that is generally continuous with a front surface of theprimary member200, as illustrated inFIG. 11 and a back surface that is generally continuous with a back surface of theprimary member200, as illustrated inFIG. 12.FIG. 13 illustrates the angular relationship between the primary andsecondary members200,210. Theprimary member200 andsecondary member210 are arranged relative to each other so that their front surfaces form an angle greater than 90° and less than 180°, specifically from 110° to about 160°. As will become apparent, the angle at which the primary andsecondary members200,210 are joined is provided so that bone screws can be introduced through thebase member120 at desired angles, as discussed further below. Accordingly, thebase member120 can be designed in any other manner that permits the bone screws to be introduced therethrough at the desired angles.
• Theprimary member200 includes at least one, and possibly two (as shown in the depicted embodiment) first bone screw holes240 extending therethrough, each configured to receive a corresponding bone screw. The first bone screw holes240 in theprimary member210 are configured such that bone screws extend through theholes240 at an angle, as illustrated inFIG. 10. For example, the first bone screw holes240 can extend through a corner that joins atop surface250 of thebase member120 to aback surface260 of thebase member120, as best shown inFIG. 12. As a result, each bone screw extending through the first bone screw holes240 can enter the bone body at an angle, as discussed further below. Each of the first bone screw holes240 is sufficiently large to allow a portion of a respective bone screw to pass therethrough but not large enough to allow a retaining portion of the bone screw through, such as the head of the bone screw. Further, each of the first bone screw holes240 has aseat265 on which the retaining portion of a respective bone screw rests. Eachseat265 has a generally concave spherical shape and the surface of the retaining portion of the bone fastener in contact with theseat265 has a complementary convex spherical configuration. Consequently, the bone screws are free to pivot on theseats265. Theprimary member200 also includes a threadedhole270 for receiving the restrainingmember fastener170.
• Thesecondary member210 includes a secondbone screw hole280 in the form of an elongated slot for receiving a bone screw. The bone screw is introduced into the secondbone screw hole280 and into a second bone body. The secondbone screw hole280 is configured such that a bone screw can slide and rotate within the slot relative to thebase member120 and generally toward theprimary member200. Thus, in use, as two adjacent bone bodies, to which thebase member120 is fixed, collapse or settle and move toward each other, the bone screw contained within the secondbone screw hole280 will slide within the slot and move with the bone body into which it extends in a direction toward theprimary member200 and the other bone body.
• At least one and possibly twoprojections283 extend upwardly from thetop surface250 of thebase member120. Theprojections283 contact a surface of the bone bodies to provide a stop when inserting thebase member120 between the bone bodies. Thebase member120 also includesholes287 provided through each of the first andsecond legs220,230. Theholes287 facilitate visualization of the fusion mass on x-rays and bone growth therethrough when theinterbody device110 is positioned between two bone bodies.
• Thebase member120 may be made of any suitable material, and can be made from titanium or a titanium alloy. The thickness of thebase member120 is not critical, and possibly ranges from about 1 mm to about 2 mm, and more specifically is about 1.6 mm. The height of thebase member120 will depend on the needs of the particular patient.
• Turning now toFIG. 15, thebone fastener150 is illustrated in further detail in accordance with an aspect of the present invention. Thebone fastener150 can comprise a bone screw, a plurality of which is used for securing theinterbody device110 to the bone bodies. Thebone fasteners150 can be made of any suitable material, and are possibly made of the same material as thebase member120, such as titanium or a titanium alloy. Thebone fasteners150 can all have the same shape, such as that shown inFIGS. 8-10. In the depicted example, the bone fasteners each have a radiusedhead290. As used herein, the term “radiused head” means that the lower portion of the bone screw head, i.e., the portion that is nearest the shank, is generally rounded, to thereby permit the bone screws to toggle within theirrespective holes240 and280. Thebone fasteners150 can have any other suitable shape that permits them to cooperate with the first and second bone screw holes240 and280 or the elongated slots ofFIGS. 24 through 29.
• Thebone fasteners150 can be undersized to permit the bone fastener to slide in a bone screw hole. For instance, the bone fastener may be positioned in a bone body such that the retaining portion, such as the head, does not rest on the seat of the hole and the portion of the bone fastener extending into a bone body is not fully embedded. In this case, it is desirable that the portion of the bone fastener extending into a bone body is substantially small. Reducing the non-embedded portion of the bone screw tends to ensure that the retaining portion of the bone fastener does not protrude outward from the hole in a manner that renders it difficult to position a retaining means over the bone fastener. To permit thebone fastener150 to slide in the hole, the diameter of the portion extending into a bone body is substantially less than the diameter of the hole. Thebone fastener150 can be positioned at one edge of the hole so that the bone fastener may slide within the diameter of the hole until it becomes in contact with the opposite edge of the hole. The hole in this case functions as an elongated slot as described with regard toFIGS. 24 through 29. In this regard, the hole has a small elongation length that allows the bone fastener to slide. Thus, the length of travel is controlled by the difference of the respective diameters of the hole and the portion of the screw extending into a bone body. In other words, the more undersized the portion of the bone fastener that extends into a bone body, the more slide length that will be available.
• The bone fasteners are secured to thebase member120 via restraining means. As stated above, the restraining means can include a restrainingplate160, an example of which is illustrated inFIGS. 16 and 17 in accordance with an aspect of the present invention. The restrainingplate160 is configured to correspond with a recessedregion300 of thebase member120 of the interbody device110 (seeFIGS. 11 and 13). More specifically, the restrainingplate160 includes a generally roundedfront side310 and a generally flatback side320. The restrainingplate160 has aflange330 formed in a top portion of the plate, theflange330 being configured to fit within a correspondinggroove340 formed in thebase member120. The use of the recessedregion300 and thegroove340 in thebase member120 facilitates proper positioning of the restrainingplate160 on thebase member120. The thickness of the restrainingplate160 is not critical, but should generally be as thin as possible. Some example thicknesses are possibly in the range from about 0.5 mm to about 2 mm, more specifically from about 1 mm to about 1.5 mm.
• Turning toFIG. 17, the restrainingplate160 includes a plurality of notches formed along the edges of itsback surface320. The notches include at least one generallyrounded notch350, possibly two, each of the generally roundednotches350 configured to correspond with one of the bone screws150. When the restrainingplate160 is fixed in place over thebase member120, the generally roundednotches350 each cover a portion of a corresponding one of the bone screws150. Thenotches350 are generally rounded so as to permit the bone screws150 to toggle within the first bone screw holes140. The restrainingplate160 can also include a substantiallyU-shaped notch360, which is curved outwardly towards the edge of the restrainingplate160. When the restrainingplate160 is fixed in place over thebase member120, the top of thebone screw150 positioned within the secondbone screw hole280 sits within theU-shaped notch360. Thus, a top of thebone screw150 is covered by the top surface of the restrainingplate160. With this design, thebone screw150 positioned within the secondbone screw hole280 is permitted to slide and toggle within the slot even when the restrainingplate160 is fixed over thebone screw150.
• The restrainingplate160 also includes anaperture370 formed therethrough. Theaperture370 in the restrainingplate160 is aligned with ahole270 in theprimary member210 of thebase member120, both of which can receive a restrainingmember fastener170 for fixing the restrainingplate160 in place over thebase member120. The restrainingmember fastener170 can be made of any suitable material well known in the art, possibly titanium or a titanium alloy. The restrainingmember fastener170 can be a screw, such as a hexagonal screw that can be turned with a hexagonal driver. Other types of fasteners can also be used, as well as any other suitable mechanism for fixing the restrainingplate160 to thebase member120. In one embodiment, the mechanism does not permanently fix the restrainingplate160 to thebase member120 so thatdevice110 can be removed if desired. The precise mechanism by which the restrainingplate160 is fixed to thebase member120 is not critical to the invention.
• In one embodiment the restrainingplate160 functions to prevent the bone screws150 from backing out of the bone bodies once the bone screws150 are screwed in. That is, thenotches350 and theU-shaped notch360 cover the bone screws150 extending through thebase member120 such that the top surface of the restrainingplate160 does not come into contact with the bone screws150. When the restrainingplate160 is fixed in place over the bone screws150, the top surface of the restrainingplate160 does not interfere or contact the bone screws150 as they toggle or slide in the bone screw hole140 orslot280. The top surface of the restrainingplate160 contacts or restricts the movement of the bone screws when the bone screws150 back out or loosen from the bone bodies. Thus, during normal use of the implanteddevice110, the restrainingplate160 does not tend to impede the movement of the bone screws150.
• In another embodiment, which is not shown, the restrainingplate160 can have a top surface and/or notches that contact or interface with the head of at least onebone screw150. The interface between the top surface or notch of the restrainingplate160 and acorresponding bone screw150 prevents thebone screw150 from backing out of the bone body and tends to exert force on thebone screw150 so as to control the movement of thescrew150 in thehole240 or slot280 of thebase member120. Depending on the surface dimensions of the restrainingplate160 and the shape of thebone screw150 head, the interface between theplate160 and abone screw150 can control the amount of toggle or slide of abone screw150. For example, the restrainingplate160 can include a notch configured to match the rounded head of acorresponding bone screw150, wherein the notch also has a stop plate or restraining surface. When thebone screw150 toggles in the slot of thebase member120, the head rotates along the interface with the corresponding notch in the restrainingplate160 until the head of thebone screw150 reaches the stop plate. In this regard, the top surface or notch of the restrainingplate160 can be designed so the interface with abone screw150 can be used to control the amount of movement or resistance abone screw150 is subject to in order to create resistance to movement thereof.
• In yet another embodiment, which is not shown, the surface portions of the restrainingplate160 that interface with the bone screws150 can be substantially angled such that the interface portions of the restrainingplate160 are flush with the top surface of thebone screw150 heads. That is, the surface portions of the restrainingplate160 that interface with the top surface of thebone screw150 heads rest flat against the heads and restrain the bone screws from toggling or rotating in the hole or slot the bone screws150 extend through. In the case which thebone screw150 extends through a slot in theinterbody device110, the restrainingplate160 can also include a stop plate that extends from the surface of the restrainingplate160 into the slot. When thebone screw150 is at one end of the slot, the stop plate extending downward into the slot can prevent thebone screw150 from sliding along the entire elongation length of the slot. The stop plate can be positioned at any point along the elongation length of the slot so that the distance thebone screw150 slides in the slot can be controlled. Subsidence resistance can also be controlled in part by the positioning of the stop plate in the slot. For example, if the stop plate is positioned near the opposite end of the slot from the end where thebone screw150 is located, thebone screw150 can slide along substantially the entire elongation length of the slot and thus subsidence resistance may be decreased. On the other hand, if the stop plate is positioned near the location of thebone screw150 in the slot, the distance thebone screw150 can slide along the elongation length of the slot is decreased and subsidence resistance may be increased.
• FIGS. 30 and 31 illustrate another embodiment of a restrainingplate160 that can be used with theinterbody device110. The restrainingplate160 ofFIGS. 30 and 31 is attached or fixed to theinterbody device110 by means of ascrew170. The restrainingplate160 covers a portion of thebone screw150 heads passing through theprimary member200 and extends downward over thebone screw150 passing through thesecondary member210. Thebone screw150 passing through thesecondary member210 is substantially covered by the restrainingplate160. As shown inFIG. 30, the restrainingplate160 can have anopen area162 that exposes thebone screw150 passing through thesecondary member210. Theopen area162 of the restrainingplate160 allows thebone screw150 to more easily slide or toggle in the aperture it passes through. As shown inFIG. 31, the restrainingplate160 rests flush against theinterbody device110 on the surfaces of theprimary member200 andsecondary member210. The shape or contour of the restrainingplate160 allows for a custom fit with theinterbody device110 such that the front portion of theinterbody device110 is substantially flat.
• Additionally, it is to be appreciated that any other suitable bone screw restraining means can be used in connection with the present invention. For example, the bone screw restraining means can comprise multiple restraining plates that cover different bone screws. Alternatively, the bone screw restraining means can comprise one or more screws with heads that overlap at least a portion of one or more bone screws to thereby prevent the bone screws from backing out.
• FIGS. 18 and 19 illustrate theinterbody device110 secured between twobone bodies380 and390 in accordance with an aspect of the present invention. Thebone bodies380 and390 can be two adjacent vertebrae and theinterbody device110 can be mounted to the vertebrae with a bone graft (not shown) between the vertebrae. More specifically, thebase member120 of thedevice110 is mounted to the vertebrae by attaching thebone fasteners150, which are located in bone screw holes240, to one of thecervical vertebrae380 to be stabilized and thebone fastener150, which is located inslot280, to the other of thecervical vertebrae390 to be stabilized. Thebase member120 is positioned such that the first andsecond legs220,230 lie generally opposite the bone graft between the two vertebrae. Thebone fasteners150 are driven into thevertebrae380,390 sufficiently so that the convex spherical configuration of thebone fasteners150 bear against theseats265 of the bone screw holes240 and secure thebase member120 against anterior surfaces of the twocervical vertebrae380,390. More specifically, thebone fasteners150 provided through the bone screw holes240 are driven through an end surface ofbone body380; and thebone fastener150 provided through theslot280 is driven through a top surface ofbone body390.
• To provide an enhanced fit, a few millimeters of bone can be trimmed or otherwise removed from a lip osteophyte of the secondvertebral body390 at an angle corresponding to the angle of thesecondary member210 of thebase member120. The trimmed surface provides a substantiallyflat surface400 for anchoring thebone screw150 into the lip osteophyte of the secondvertebral body390. The surface also accommodates sliding of the tab as the teeth subside into the secondvertebral body390.
• The angles of the bone screws150 relative to the bone surfaces of thevertebral bodies380,390 are important. The lip osteophyte is the strongest part of the bone, and thus angling the bone screws150 through the lip osteophyte increases the ability of thebase member120 to stay anchored to thevertebral bodies380,390. Moreover, by being angled, eachbone screw150 is positioned along an angle of rotation of a correspondingvertebral body380,390 as well as an angle of settling of thevertebral body380,390. This places eachscrew150 in a protected position against motion of the spinal column. As a result, significant shear forces are not exerted on thescrews150 as thevertebral bodies380,390 rotate and settle.
• Afirst guide tool410 as illustrated inFIG. 20 can be provided to allow a surgeon to hold and position thebase member120 against the bone, and to accurately drill into the bone. Theguide tool410 includes ahandle420 for holding and manipulating a position of theguide tool410. A projection (not shown) extends from a base portion of theguide tool410 and is configured to engagehole270 in theprimary member200 of the base120 to hold theguide tool410 in position. When thehandle420 is properly engaged with thebase member120, a pair ofguide tubes430 is properly lined up with corresponding bone screw holes240. The surgeon then inserts a drill or center punch (not shown) through one of theguide tubes430 to drill a hole in the bone, through thescrew hole240. Then, after removing the drill, the surgeon inserts abone screw150 held at the end of a suitable driver (not shown) through theguide tube430, and screws it into the bone. The process is repeated until the desired number of screws are placed, leaving the base member secured to the bone via the first bone screw holes240. Or, since thefirst guide tool410 includes twoguide tubes430, the bone screws150 can be inserted at substantially the same time.
• Asecond guide tool440 is illustrated inFIG. 21 is also provided to allow a surgeon to hold and position thebase member120 against the bone, and to accurately drill into the bone. More specifically, thesecond guide tool440 is employed to drill abone screw150 into thebone slot280. Thesecond guide tool440 includes two substantiallyround projections450 that engage correspondingnotches460 provided between thesecondary member210 of thebase120 and anadjacent interface member130 provided on each side of the secondary member210 (seeFIGS. 11 and 12) to hold thesecond guide tool440 in position. As above, the surgeon then inserts a drill (not shown) through aguide tube470 to drill a hole in the bone, through thescrew slot280. Then, after removing the drill, the surgeon inserts abone screw150 held at the end of a suitable driver (not shown) through theguide tube470, and screws it into the bone. It should be noted that one function of the guide is to locate the screw at the end of the slot so the screw travel can match subsidence of the teeth. If for example the screw was placed in the center of the slot it would bottom out in the slot before the teeth had fully embedded.
• In another embodiment, thebone screw150 configured to pass through the apertures in thebase member120 can have pointed ends which comprise a cutting flute on the tip. The cutting flute at the tip of thebone screw150 allows the screw to be self-drilling or self-tapping. Thus, the use of abone screw150 having a self-drilling or self-tapping tip makes the use of a drill or center punch optional.
• Turning back toFIGS. 18 and 19, once the bone screws150 are inserted into the bone screw holes240 and thebone screw slot280, the restrainingplate160 is placed over the base member and fixed in place to prevent thescrews150 from “backing out” of the screw holes240,280. Thesecond bone screw150 that extends through thebone screw slot280 is nonetheless permitted to slide along the length of theslot280, even when the restrainingplate160 is secured in place. Thus, second thebone screw150 and thebone screw slot280 cooperate to control any lateral or rotary movement of one vertebral body relative to an adjacent vertebral body during “settling” of the bone. Further, the angled orientation of thesecond member210 provides thebase member120 with resilient properties, for example, enabling thebase member120 “flex” when one vertebra is rotated relative to an adjacent vertebrae.
• As shown inFIG. 19, theinterbody device110 of the present invention has a substantially low profile. Namely, the base member of the present invention is designed to have an outer periphery that coincides with or generally matches the outer diameter of the cortex. The top surface of the base sits at, and possibly below, the top surface of the vertebral bodies. As such, theinterbody device110 of the present invention does not have any parts that would significantly interfere with or irritate the trachea, esophagus, and/or other anatomic structures of the patient.
• Another advantage of theinterbody device110 is that it is stackable. Frequently after a bone graft is inserted and a bone plate joined to the surrounding vertebral bodies, for example, C4 and C5, an adjacent disk, for example, between C5 and C6, subsequently deteriorates. With traditional bone plates, it would be necessary to remove the plate from C4-C5 before attaching a second bone plate to C5 and C6 because each plate covers a significant surface of the vertebral body. To remove a bone plate, it is necessary dissect scar tissue, which can have a negative impact on the patient. In contrast, theinterbody device110 of the present invention covers an insignificant portion of the top surfaces of the vertebral bodies to which it is attached, instead being located primarily between the vertebral bodies. As a result, multiple interbody devices can be introduced over adjacent bone grafts (i.e., between a common vertebral body) so that two interbody devices are attached to a common vertebral body without the bone plate systems contacting one another. Thus, subsequent procedures where new bone grafts are to be inserted do not require the removal of a pre-existing device prior to introduction of a new device. The depicted systems where the bone screws are provided in a generally triangular arrangement further enhance the stacking ability of the interbody devices of the invention.
• It is to be appreciated that a kit having base plates of different sizes, bone screws of differing lengths and restraining plates complementary to the base plates can be provided. For instance, because of the different physical dimensions of the patients on whom the invention is used, it is considered that bone plate systems of correlative dimensions be available. The present invention is capable of being provided in various sizes for that purpose.FIGS. 22 and 23 illustrate examples of a base member and interbody device, respectively, having a larger size than theinterbody device110 described with respect toFIGS. 8-20. The kit may further comprise a tack tool, a drilling tool, tapping tool and/or one or more screw driving tools.
• As noted above, all of the bone screws150 may be permitted to toggle, or pivot, even after the restrainingplate160 is fixed over thebase member120. The ability of thescrews150 to toggle permits theinterbody device110 to migrate and self-center after it has been implanted.
• Thebase member120 is configured such that when first installed on the cervical vertebrae, theinterface members130 contact a surface of at least one of the bone bodies. For instance, in the present example, thebase member120 is positioned between thevertebrae380 and390 such that thetop surface250 of thebase member120 contacts an end surface of onevertebral body380 and theinterface members130 contact an end surface of the othervertebral body390. As discussed above, theinterface members130 are configured such that substantially immediate penetration does not occur. Rather, theinterbody device110 gradually subsides as the vertebrae and bone graft fuse to share in the weight bearing during settling of the vertebral bodies. Specifically, as the vertebral bodies move toward each other during settling, theinterface members130 will contact and enter the secondvertebral body390 with increased resistance to subsidence. This contact controls the rate of settling.
• Theinterbody device110 provides such an interface design by controlling the height, size, shape, and spacing of the teeth that interdigitate with the endplate of the vertebral body. In addition screw fixation is provided. The length of screw travel in theslot280 is possibly matched to the height of theinterface members130. Accordingly, subsidence is arrested once thebone screw150 reaches the intended limit as provided by theslot280. Screw fixation also addresses expulsion of the interbody device, a concern common to all interbody devices. Theinterbody device110 accommodates a large graft surface area further increasing the probability that fusion will occur.
• Theinterbody device110 as described above can have a variety of alternative configurations. Various configurations can include, but are not limited to, those shown inFIGS. 24 through 29.
• FIG. 24 illustrates aninterbody device110 comprising abase member120 having aprimary member200 and asecondary member210. Theprimary member200 includes at least one firstelongated slot242 extending therethrough that is configured to receive a corresponding bone screw or fastener. Further, thesecondary member210 includes at least one secondelongated slot280 extending therethrough that is configured to receive a bone screw. Theelongated slot280 of thesecondary member210 is similarly referenced and described above with regard toFIGS. 11 and 12. Theprimary member200 also includes a threadedhole270 for receiving a restraining means configured to mitigate the backing out of at least one bone fastener from a bone body.
• Theinterbody device110 ofFIG. 24 can include at least one (two are shown)projection283 that extends upward from thetop surface250 of theprimary member200. Theprojection283 provides a base or shelf that contacts a bone body in order to stop theinterbody device110 against a corresponding bone body upon insertion into a human. Although not shown inFIG. 24, the at least oneprojection283 can alternatively be positioned to extend from the bottom surface of theprimary member200. In one example,FIG. 27 illustrates twoprojections283 extending from the bottom surface of the primary member.
• Theprimary member200 of theinterbody device110 has a plurality ofinterface members130 extending from the bottom surface. Theinterface members130 can comprise, for example, teeth, knife-edges, spikes, posts, pegs, or combinations thereof. Theinterface members130 provide a controlled subsidence interface between theinterbody device110 and a corresponding bone body. Although not shown inFIG. 24, interface members may also extend from the top surface of theprimary member200 so as to provide two controlled subsidence interfaces between theinterbody device110 and two adjacent bone bodies. In one example,FIGS. 25 and 27 illustrate various configurations ofinterface members132 that may extend from the top surface of theprimary member200. To promote controlled subsidence, the interface members may extend from the top or bottom surface of theprimary member200 in a direction that is aligned with an elongate direction of two adjacent bone bodies, such as two vertebrae in a spine. For example,FIGS. 18 and 19 illustrate theinterbody device110 positioned between two adjacent bone bodies.
• As illustrated inFIG. 24, theprimary member200 can have twoelongated slots242 configured such that bone screws extend through theslots242 at an angle. Thus, each bone screw extending through the firstbone screw slots242 can enter a bone body at an angle. Theelongated slots242,280 of the primary andsecondary members200,210 are sufficiently large to allow a portion of a bone screw, such as a threaded shaft that extends into a bone body, to pass therethrough but not large enough to allow a retaining portion of the bone screw through, such as the head of the bone screw. The general aspects of the bone screw or bone fastener are described above with regard toFIG. 15. Theelongated slots242,280 may have a seat portion on which the retaining portion of a bone screw can rest. The seat portion of theslots242,280 has a generally concave spherical shape and the surface of the retaining portion of a bone screw in contact with the seat has a complementary convex spherical configuration. In this regard, the retaining portion, such as the head, of a bone screw is free to pivot on the seat of theelongated slot242,280.
• Theelongated slots242,280 of the primary andsecondary members200,210 inFIG. 24 are configured to permit bone screws extending therethrough to slide and rotate along the elongation length of theslots242,280 during controlled subsidence. In other words, the bone screws can slide relative to theinterbody device110 as theinterface members130 progressively penetrate into a corresponding bone body over time. As the bone screws slide along the elongation length of theslots242,280, at least one bone screw can eventually slide against the end of aslot242,280 it extends through. In this case, the bone screw becomes secured at the end of thecorresponding slot242,280 such that the bone screw can no longer slide relative to theinterbody device110 as theinterface members130 may continue to penetrate into the corresponding bone body. Subsidence resistance increases as the at least one bone screw becomes secured at the end of theslot242,280 and can no longer slide relative to theinterbody device110. At the end of theslot242,280, the bone screw can toggle in order to assist theinterface members130 to further penetrate into a corresponding bone body.
• AlthoughFIG. 24 illustratesinterface members130 extending only from the bottom surface of theprimary member200, the following description of the affect the elongation length of theslots242,280 may have on subsidence resistance is based oninterface members130,132 extending from the bottom and top surface of theprimary member200, for example, as illustrated inFIGS. 12, 25 and 27. Eachelongated slot242,280 ofFIG. 24 can have an elongation length that is less than, about the same as or greater than the height of at least onesingle interface member130,132. Alternatively, eachelongated slot242,280 can have an elongation length that is less than, about the same as or greater than the height of anysingle interface member130,132.
• The elongation length of the at least oneslot242 in theprimary member200 can be substantially the same as, less than or greater than the elongation length of the at least oneslot280 in thesecondary member210 depending on the desired controlled subsidence profile. Varying the elongation length of at least oneslot242,280 can mitigate the effects that poor bone quality or an irregular surface of a bone body can have on the controlled subsidence profile. In the case that the elongation length of any oneslot242,280 is matched to or about the same as the height of theinterface members130,132, further subsidence resistance can occur after the bone screw slides relative to theinterbody device110 the intended limit as provided by the elongation length of theslot242,280. As at least oneinterface member130,132 becomes fully penetrated into a bone body, at least one bone screw becomes positioned at the end of theslot242,280 the screw extends through. As the bone screw rests at the end of theslot242,280, further subsidence resistance can occur as the bone screw toggles at the end of theslot242,280. The toggling of the bone screw at the end of theslot242,280 permits theinterface members130,132, of which somemembers130,132 may not be fully embedded in a bone body, to further penetrate into the bone body. In theory, without being bound thereto, one reason for the continued penetration of a fully-embeddedinterface member130 into a bone body is poor bone quality. In another aspect, the surface of a bone body can be irregular such that a substantially flat or flush surface is not available on which the shelf-like bottom or top surface of theprimary member200 can rest. The irregular surface of a bone body can result in some of theinterface members130 not becoming fully embedded in a bone body. Depending on the degree of irregularity of a bone body surface, some of theinterface members130,132 may also not be in contact with a bone body when thebone screw150 slides relative to theinterbody device110 to the end theslot242,280. Therefore, as discussed above, toggling of the bone screw at the end of theslot242,280 can force theinterface members130,132 that are not fully embedded in a bone body to penetrate further and become fully embedded.
• In the case that the elongation length of any oneslot242,280 is less than the height of theinterface members130,132, the bone screw tends to not reach or slide to the end of theslot242,280 prior to anysingle interface member130,132 becoming fully embedded into a bone body. Thus, the subsidence resistance is increased when the elongation length of any oneslot242,280 is less than the height of at least onesingle interface members130,132. In use, as theinterface members130,132 begin to penetrate into a bone body, but before any single member becomes fully embedded, a bone screw may slide along the elongation length of theslot242,280 and reach the end of theslot242,280. Being positioned at the end of theslot242,280, the bone screw is forced to toggle so the interface members can further penetrate into a bone body and thus subsidence resistance is increased. In this instance, toggling of the bone screw at the end of theslot242,280 can assist theinterface members130,132 that are not fully embedded in a bone body to penetrate further and become fully embedded.
• In the case that the elongation length of any oneslot242,280 is greater than the height of theinterface members130,132, the bone screw tends to not reach or slide to the end of theslot242,280 prior to anysingle interface member130,132 becoming fully embedded into a bone body. Increasing the length a bone screw can travel or slide in aslot242,280 can decrease subsidence resistance. For example, an irregular bone body surface can cause at least oneinterface member130,132 to become fully embedded in a bone body before a bone screw slides relative to theinterbody device110 to the end of theslot242,280. The bone screw in this instance can continue to slide along the elongation length of theslot242,280 as the remaininginterface members130,132 continue to further penetrate into a bone body surface. The additional distance or length thebone screw150 can travel before reaching the end of theslot242,280 generally makes it unnecessary for thebone screw150 to toggle inslot242,280 to ensure that theinterface members130,132 become fully embedded in a bone body. The subsidence resistance profile in this case would be substantially lower because, in part, the bone screw generally does not need to toggle in theslot242,280 in order to ensure theinterface members130,132 become fully embedded. Further, thebone screw150 in this case will not generally rest at the end of theslot242,280, which can increase the subsidence resistance.
• In another aspect, the elongation length of any oneslot242,280 of theinterbody device110 ofFIG. 24 can be substantially zero. Theslot242,280 in this instance tends to function substantially the same as a bone screw hole as described above, for example, with regard tohole240 ofFIGS. 11 and 12. Thus, theslot242,280 has substantially no elongation over which a bone screw can travel along. In this regard, a bone screw is forced to toggle in theslot242,280 to assist penetration of theinterface members130,132 into at least one bone body and thus subsidence resistance is increased in this configuration. That is, a stiff construct comprising at least one bone body and theinterbody device110 results from the elongation length of any oneslot242,280 being substantially zero.
• As can be seen above with regard to theinterbody device110 ofFIG. 24, the subsidence resistance profile can be controlled and/or affected by the combination of the elongation length of anysingle slot242,280 and the shape, location and height of theinterface members130,132. Each of these features of the present invention can be adjusted, modified or combined in order to compensate for poor bone quality, an irregular surface of a bone body or to ensure full penetration of theinterface members130,132 into at least one bone body.
• Turing toFIG. 25, theinterbody device110 can haveinterface members132 on the top surface of the first andsecond legs220,230 of theprimary member200. Theinterbody device110 can further haveinterface members130 extending from the bottom surfaces of theprimary member200, thefirst leg220 and thesecond leg230.FIG. 26 illustratesinterface members130,132 extending from the top and bottom surface of a representative leg of theprimary member200. Although not shown inFIG. 25, theinterbody device110 can haveadditional interface members132 which extend upward from thetop surface250 of theprimary member200. In one example,FIG. 27 illustratesinterface members132 extending upward from thetop surface250 of theprimary member200. Theinterbody device110 ofFIG. 25 has at least onebone screw slot242 in theprimary member200 and at least onebone screw slot280 in thesecondary member210. As shown,FIG. 25 illustrates twobone screw slots242 in theprimary member200 and onebone screw slot280 in thesecondary member210. In this embodiment, theinterbody device110 provides controlled subsidence at the interface of thetop interface members132 with a corresponding bone body and at the interface of thebottom interface members130 with a corresponding bone body. Theprimary member200 also includes a threadedhole270 for receiving a restraining means configured to mitigate the backing out of at least one bone fastener from a bone body.
• Eachelongated slot242,280 ofFIG. 25 can have an elongation length that is less than, about the same as or greater than the height of at least onesingle interface member130,132. Further, eachelongated slot242,280 can have an elongation length that is less than, about the same as or greater than the height of anysingle interface member130,132. The at least oneslot242 in theprimary member200 and at least oneslot280 in thesecondary member210 can have about the same or varying elongation lengths depending on the desired controlled subsidence profile. As discussed above with regard toFIG. 24, the elongation length of eachslot242,280 in theinterbody device110 ofFIG. 25 can also be modified to increase or decrease the subsidence resistance as theinterface members130,132 penetrate into corresponding bone bodies.
• In one aspect, the height of theinterface members130,132 may be about half of the overall desired controlled subsidence distance. For example, if it is desirable to have a total of 2 mm of penetration into the corresponding bone bodies, thetop interface members132 andbottom interface members130 may each respectively have a height of about 1 mm. In another aspect, theinterface members130,132 may each respectively have about 1 to 99 percent of the overall desired subsidence control. In yet another aspect,interface members132 can be located on only the top surface of thefirst leg220,second leg230 or primary member200 (seeFIG. 27) or theinterface members130 can be located on only the bottom surface of the first andsecond legs220,230 or the primary member200 (not shown). In this case, controlled subsidence would only occur at the interface of thetop members132 and a corresponding bone body or at the interface of thebottom members130 and a corresponding bone body.
• FIG. 27 illustrates aninterbody device110 having a pair ofelongated slots242 extending through theprimary member200. Theinterface members132 of thedevice110 extend from the top surface of theprimary member200 and first andsecond legs220,230. Thesecondary member210 has a singlebone screw hole282 configured for receiving a bone screw.Projections283 extend from the bottom surface of theprimary member200 and provide a shelf or surface to stop theinterbody device110 against a bone body upon insertion into a spine. Theprojections283 may be positioned on the bottom surface of theprimary member200 in order to increase the area on thetop surfaces250 of theprimary member200 and first andsecond legs220,230 on which theinterface members132 may be located.
• In another aspect, thesingle screw hole282 in thesecondary member210 of theinterbody device110 ofFIG. 27 may be anelongated slot280 and the pair ofelongated slots242 of theprimary member200 may be a pair of screw holes240. For example, theinterbody device110 ofFIG. 28 illustrates aninterbody device110 having two bone screw holes240 in theprimary member200 and anelongated slot280 in thesecondary member210. Theprimary member200 also may include a threadedhole270 for receiving a restraining means configured to mitigate the backing out of at least one bone fastener from a bone body.
• FIG. 29 illustrates yet another alternative configuration of theinterbody device110. Theinterbody device110 ofFIG. 29 may be configured for insertion into a spine such that thesecondary member210 extends upward from a surface of theprimary member200. That is,FIG. 29 illustrates an inverted view of theinterbody device110 shown in the other Figures herein. Theinterface members132, which generally extend downward as representatively shown inFIGS. 24 through 28, extend upward in the direction of thesecondary member210. In this embodiment, theinterbody device110 provides controlled subsidence at the interface of thetop interface members132 and a corresponding bone body. Theprimary member200 andsecondary member210 are arranged relative to each other so that their front surfaces at their interface form an angle greater than 90° and less than 180°, or about 110° to about 160°. As shown, theprimary member200 can include at least onebone screw hole240 and thesecondary member210 can include at least oneelongated slot280. Theelongated slot280 can have an elongation length that is less than, about the same as or greater than the height of at least onesingle interface member132. Alternatively, theelongated slot280 can have an elongation length that is less than, about the same as or greater than the height of anysingle interface member132. As discussed above with regard toFIG. 24, the elongation length ofslot280 in theinterbody device110 ofFIG. 29 can be modified to increase or decrease the subsidence resistance as theinterface members132 penetrate into a bone body. Further, as shown in the Figures herein, theprimary member200 may also include a threadedhole270 for receiving a restraining means configured to mitigate the backing out of at least one bone fastener from a bone body.
• Although not shown inFIG. 29, theinterbody device110 can have additional interface members extending from a bottom surface of theprimary member200, for example, as illustrated inFIGS. 25 and 27. In another aspect, thesecondary member210 may include an aperture other than theelongated slot280 shown, such a bone screw hole as shown inFIG. 27. In yet another aspect, theprimary member200 may include an aperture other than the bone screw holes240 shown, such as an elongated slot as shown inFIGS. 24 and 25.
• In another embodiment, the various configurations of theinterbody device110, including but not limited to those shown inFIGS. 24 through 29, may include a plurality of interface members of any desirable height and shape. In one example, as shown inFIG. 24, each of the plurality ofinterface members130 extending upward from the surface of theprimary member200 can have the same height. Alternatively, the plurality ofinterface members130 ofFIG. 24 may have different heights such that at least one of the plurality ofmembers130 extending from theprimary member200 has a height substantially not equal to at least one other interface member130 (not shown). In this regard, the profile ofinterface members130 extending from a surface of theprimary member200 may be varied or contoured to the surface of a corresponding bone body, such as an irregular or substantially non-flush surface for theinterbody device110 to rest upon. The shape and height of the plurality ofinterface members130 may be modified to fit into or conform with the irregularities of a bone body surface, such a peaks, bumps, cavities, voids and the like. Such irregularities may reduce the number ofinterface members130 which fully penetrate a bone body and the depth to whichinterface members130 may become embedded. Thus, irregular bone body surfaces provide different controlled subsidence profiles.
• While shown embodiments of the present invention are described for supporting adjacent cervical vertebrae in the anterior region of the vertebrae, persons skilled in the art would recognize that the bone plate of the present invention may be utilized to support adjoining thoracic and lumbar vertebrae in the lateral or posterior regions of the vertebrae. Further, the device and method of the invention is not limited to vertebral bodies, but can also be used to join two other pieces of bone in other parts of the body.
• Referring initially toFIG. 32, an example of a device orimplant device510 is illustrated in accordance with an aspect of the present invention. Theimplant device510 is configured to fix and secure two or more bone bodies. As used herein, the phrase “bone bodies” is intended to include individual bones as well as fragments or portions of bones. For example, the bone bodies can be two adjacent vertebrae and theimplant device510 can be mounted to the vertebrae with graft material (not shown) between the vertebrae. More specifically, and as will be described in further detail below, theimplant device510 can fix and secure adjacent vertebrae that have had cartilaginous disc between the vertebrae replaced with material that promotes the fusion of the vertebrae such as a graft of bone tissue or some other similar material. It is to be appreciated that one aspect that is addressed by the present invention is load sharing with a graft.
• As shown inFIG. 32, the configuration of theimplant device510 includes abase member520 having a plurality of protrusions orinterface members530 extending from a surface of thebase member520. Thebase member520 has atop surface650 and abottom surface651. As shown, theinterface members530 extend from thebottom surface651 of thebase member520. Although not shown, theinterface members530 can alternatively extend from only thetop surface650 of thebase member520, or from both thetop surface650 and the bottom surface of thebase member520 in order to provide two controlled subsidence interfaces between theimplant device510 and adjacent bone bodies. Theinterface members530 are configured to contact at least one surface of a bone body to provide subsidence control for theimplant device510. Theinterface members530 can include, for example, teeth, knife-edges, spikes, posts, pegs, or combinations thereof.
• Thebase member520 is configured such that when first inserted between two adjacent bone bodies, theinterface members530 contact a surface of at least one of the bone bodies. Theinterface members530 are configured such that substantially immediate penetration into a bone body occurs. Theimplant device510 gradually subsides as the bone bodies and bone graft fuse to share in the weight bearing during settling of the bone or vertebral bodies. Specifically, as the bone bodies move toward each other during settling, theinterface members530 will penetrate the bone bodies with increased resistance to subsidence.
• Controlled subsidence relates to resistance to subsidence and total amount of subsidence. To promote controlled subsidence, theinterface members530 may extend from a surface of the base member in a direction that is aligned with an elongate direction of two adjacent bone bodies, such as two vertebrae in a spine. The interface members are thus configured to provide progressive penetration into a bone body over a period of time. The subsidence profile, which is a relationship between an applied load and an amount of settling theimplant device510 experiences when secured to the bone bodies, is dependent on the configuration or shape of theinterface members530. For example, theinterface members530 can readily penetrate into a bone body initially and then slow down as more of the interface member cross section embeds. The height (H) of theinterface members530 relative to the depth of penetration into a corresponding bone body. Generally, when theimplant device510 has subsided to a point where the interface members are fully embedded in the bone, the applied load will be distributed across the entire surface of theimplant device510 and subsidence resistance will increase. The controlled subsidence relationship between theinterface members530 and the at least one corresponding bone body that themembers530 extend into is described herein.
• Thebase member520 of theimplant device510 includes aprimary member600 and asecondary member610, which extends from and is angled relative to theprimary member600. Theprimary member600 forms an enclosed loop or peripherally-surroundedchamber692 that is configured to receive and hold fusion material, such as a bone graft. As shown, thechamber692 is peripherally-surrounded, but not fully enclosed, such that bone bodies residing above and below thechambers692 can be in contact with fusion material located in thechamber692. It is to be appreciated, and for the description purposes of the present invention herein, the peripherally-surroundedchamber692 can be positioned at any angle in order to accommodate the orientation of bone bodies to be fused together. In any case, thechamber692 can mitigate lateral shift of the fusion material and control subsidence of adjacent bone bodies as they set during fusion. Subsidence is further controlled by the presence of theinterface members530 that extend from a surface of thebase member520. In the present embodiment, the primary andsecondary members600,610 are contiguous and unitary. Thesecondary member610 has a front surface that is generally continuous with a front surface of theprimary member600, and a back surface that is generally continuous with a back surface of theprimary member600. Theprimary member600 andsecondary member610 are arranged relative to each other so that their front surfaces form an angle. Of course, the angle is not of great importance and typically depends upon a compromise between low profile and the amount of bone that would need to be removed. Suffice to say that the angle can be any angle (e.g., greater than 90° and less than 180°). However, a typical angle would be in the range, from about 140° to about 170°. The angle at which the primary andsecondary members600,610 are joined is provided so that bone screws can be introduced through thebase member520 at desired angles. Alternatively, thebase member520 can be designed in any other manner that permits the bone screws to be introduced there through at the desired angles.
• Theprimary member600 can form the peripherally-surroundedchamber692 to be of any shape or size to accommodate adjacent bone bodies of various shapes, sizes and positions. The peripherally-surroundedchamber692 of the present invention is designed to have an outer periphery that coincides with or generally matches the outer diameter of the cortex or adjacent vertebrae. The top surfaces of theimplant device510 sit at, and possibly below, the top surface of the vertebral bodies. As such, theimplant device510 of the present invention does not have any parts that would significantly interfere with or irritate the adjacent anatomic structures of the patient. As shown, the peripherally-surroundedchamber692 has a rounded-edge rectangular shape that would adequately accommodate two adjacent vertebrae of a spinal column. Theprimary member600 generally forms the vertically-open and peripherally-surroundedarea692, when viewed in the implanted position in a spinal column, that can receive and hold fusion material between two or more bone bodies. In use, theprimary member600 laterally extends around an amount of fusion material, such as a bone graft, in order to mitigate lateral shift of the graft and control subsidence of adjacent vertebrae as the vertebrae set during fusion. The fusion material can be packed into the peripherally-surroundedchamber692 formed by theprimary member600. Thechamber692 of theimplant device510 creates a one-piece fusion material housing that substantially reduces the need for other devices that may be necessary to fuse multiple bone bodies together. The peripherally-surroundedchamber692 adequately houses fusion material that would generally be supported by a cage design implant. In this case, a plate would generally also be needed to keep the bone bodies and the cage in the desired location. Theimplant device510 described herein significantly reduces the cost associated with multiple-device fusion methods such as those associated with the above cage and plate combination devices.
• Another advantage of theimplant device510 is that it is stackable. Theimplant device510 of the present invention covers an insignificant portion of the top surfaces of the vertebral bodies to which it is attached. As a result, multiple implant devices can be introduced over adjacent bone grafts (i.e., between a common vertebral body) so that twoimplant devices510 are attached to a common vertebral body withoutdevices510 contacting one another. Thus, subsequent procedures where new bone grafts are to be inserted do not require the removal of a pre-existing device prior to introduction of a new device. The depicted systems where the bone screws are provided in a generally triangular arrangement further enhance the stacking ability of theimplant devices510 of the invention. It is to be appreciated that theimplant device510 can be of different scales or sizes, have differing bone screw lengths and restraining plates that are complementary to different physical dimensions of the patients on whom the invention is used and the spinal location or level at which the device is implanted. The present invention is capable of being provided in various sizes for that purpose.
• The peripherally-surroundedchamber area692 provides a retaining region or open area into which fusion material can be packed or loaded. It is possible to load fusion material, such as particulate graft material including bone chips and/or bone paste, into thechamber692 prior to the insertion of theimplant device510 between adjacent bone bodies such as vertebrae. Bone chips and/or bone paste and possibly in combination with growth factors can be used in place of a block of bone graft material. Often it is the case that bone chips and bone paste are more easily retained in a peripherally-surroundedchamber692 as opposed to animplant device510 which has an open posterior end. Thus, a combination of bone chips and bone paste is better retained in a center region of animplant device510 such as that provided in the Figures shown herein.
• In accordance with another aspect of the present invention, any portion or theentire implant device510 can be constructed from radiotransparent or radiolucent materials. Specifically, in order to facilitate radiographic evaluation of the fusion material and the corresponding bone bodies, thebase member520,primary member600,secondary member610, any other portion or component of theimplant device510 or combinations thereof can be constructed from radiotransparent or radiolucent materials. For example, theentire implant device510 can be constructed from radiolucent material. Radiolucent materials permit x-rays to pass through components of theimplant device510 so that developed x-ray pictures provide more visibility of the fusion material and bone bodies without significant interference, such as imaging artifacts, caused by thedevice510. Radiolucent materials enable clear visualization through imaging techniques such as x-ray and computer tomography (CT), whereas traditional metallic or alloy implant materials that are radiopaque can generate imaging artifacts and scatter that prevent a comprehensive inspection of the surrounding tissue, bone and fusion material. Thus, radiolucent materials allow for clearer imaging of bone bodies and fusion materials.
• Radiolucent materials can include, but are not limited to, polymers, carbon composites, fiber-reinforced polymers, plastics, combinations thereof and the like. One example of a radiolucent material that can be used with the aspects of the present invention described herein is PEEK-OPTIMA® polymer supplied by Invibio Inc., Greenville, S.C. The PEEK-OPTIMA® polymer is a polyaromatic semicrystalline thermoplastic known generically as polyetheretherketone. The PEEK-OPTIMA® polymer is a biocompatible and inert material. Known alternatives to PEEK-OPTIMA® include, but are not limited to, biocompatible polymers such as ENDOLIGN® polymer composite supplied by Invibio Inc., Greenville, S.C. The ENDOLIGN® polymer is a biocompatible carbon fiber-reinforced thermoplastic material. Radiolucent materials, including those described above, can optionally be doped or combined with radiopaque materials in different concentrations in order to vary the level of x-ray contrast and/or visual characteristics. The portions of theimplant device510 constructed from radiolucent material can be prepared by any conventional technique known in the art such as machining, injection molding or compression molding.
• In another embodiment, theimplant device510 can include a combination of components constructed from both radiolucent materials and radiopaque materials. Radiopaque materials are traditionally used to construct devices for use in the medical device industry. Radiopaque materials include, but are not limited to, metal, aluminum, stainless steel, titanium, titanium alloys, cobalt chrome alloys, combinations thereof and the like. Radiopaque materials tend to obstruct x-rays and thus restrict x-ray visibility to the regions in which the materials are located. However, radiopaque materials generally have structural characteristics that are advantageous with regard to medical devices. That is, some radiolucent materials lack the strength and/or rigidity of radiopaque materials and certain design modifications may be made to provide adequate structural integrity of theimplant device510. Radiopaque materials generally have increased rigidity as compared to radiolucent materials and thus radiopaque materials may tend to maintain bone body alignment despite the rigorous pressures and forces generated by a patient implanted with theimplant device510. Thus, it may be desirable to construct portions of theimplant device510 from radiopaque materials such as metal and other portions of theimplant device510 from radiolucent materials so that a desired level of strength and/or rigidity is obtained and also x-ray visibility is enhanced. For example, as shown inFIG. 35, thechamber member696 connected to the first andsecond legs620,630 of theprimary member600 can be constructed from radiolucent material in order to enhance the x-ray visibility of the fusion material located in the peripherally-enclosed area formed by thechamber member696 and first andsecond legs620,630 of theprimary member600 and the surrounding bone bodies. However, it is to be appreciated that radiopaque material may be used in otherwise radiolucent devices for other reasons. For example, devices that are primarily radiolucent may include radiopaque markers such that the location of the device may be readily ascertained.
• Thebase member520 of theimplant device510 can include a plurality of apertures, each of which is configured to receive a corresponding bone fastener or screw550 there through. Thebone fastener550 can include a bone screw, a plurality of which is used for securing theimplant device510 to adjacent bone bodies. Thebone fasteners550 can be made of any suitable material, such as titanium or a titanium alloy, a radiolucent material, a radiopaque material, or combinations thereof. The plurality ofbone fasteners550 can all have the same shape, such as that shown inFIGS. 32 and 33. In the depicted examples, the bone fasteners each have a radiusedhead690. As used herein, the term “radiused head” means that the lower portion of the bone screw head, i.e., the portion that is nearest the shank, is generally rounded, to thereby permit the bone screws to toggle within theirrespective holes640 andslots680.
• In another embodiment, the bone screws550 configured to pass through the apertures in thebase member520 can have pointed ends which include a cutting flute on the tip. The cutting flute at the tip of thebone screw550 allows the screw to be self-drilling or self-tapping. Thus, the use of abone screw550 having a self-drilling or self-tapping tip makes the use of a drill or center punch optional.
• For an enhanced fit of theimplant device510, a portion of bone can be trimmed or otherwise removed from a lip osteophyte of a bone body at an angle corresponding to bone screw holes640,680. The angles of the bone screws550 relative to the bone surfaces of the bone bodies can affect the anchoring of bone screws550. For example, the lip osteophyte is the strongest part of a vertebra, and thus angling the bone screws550 through the lip osteophyte increases the ability of thebase member520 to stay anchored to the vertebral bodies. By being angled, eachbone screw550 is positioned along an angle of rotation of a corresponding bone body as well as an angle of settling of the bone body. This configuration places eachscrew550 in a protected position against motion of the spinal column. As a result, significant shear forces are not exerted on thescrews550 as the vertebral bodies rotate and/or settle.
• Theprimary member600 includes at least one, and possibly two as shown, first bone screw holes640 extending there through, each being configured to receive a corresponding bone fastener orscrew550. The first bone screw holes640 in theprimary member600 are located on the front face of theprimary member600 and face outward from the patient when theimplant device510 is inserted. The bone screw holes640 are configured such that the bone screws550 extend through theholes640 at an angle. As a result, each bone screw extending through the first bone screw holes640 can enter the bone body at an angle. Each of the first bone screw holes640 is sufficiently large to allow a portion of arespective bone screw550 to pass there through but not large enough to allow a retaining portion of the bone screw through, such as thehead690 of the bone screw. Further, each of the first bone screw holes640 has aseat665 on which the retaining portion of a respective bone screw rests. Eachseat665 has a generally concave spherical shape and the surface of the retaining portion of thebone screw550 in contact with theseat665 has a complementary convex spherical configuration. Consequently, the bone screws550 are free to pivot on theseats665. Theprimary member600 also includes a threadedhole670 for receiving a restraining means configured to mitigate the backing out of at least one bone fastener from a bone body.
• Thesecondary member610 includes a secondbone screw hole680 in the form of an elongated slot for receiving a bone screw. The bone screw is introduced into the secondbone screw hole680 and into a second bone body. The secondbone screw hole680 is configured such that a bone screw can slide and rotate within the slot relative to thebase member520 and generally toward theprimary member600. Thus, in use, as two adjacent bone bodies, to which thebase member520 is fixed, collapse or settle and move toward each other, the bone screw contained within the secondbone screw hole680 will slide within the slot and move with the bone body into which it extends in a direction toward theprimary member600 and the other bone body. It is worth noting that since the slot is at an angle to the surface features, it is actually longer in the plane of the secondary member than the surface features are tall. In other words, the slot provides screw movement in the vertical direction equivalent to the height of the surface features.
• At least one and possibly twoprojections683 extend upwardly from thetop surface650 of thebase member520. Theprojections683 contact a surface of the bone bodies to provide a stop when inserting thebase member520 between the bone bodies. Theprojection683 provides a base or shelf that contacts a bone body in order to stop theimplant device510 against a corresponding bone body upon insertion into a patient. Although not shown inFIG. 32, the at least oneprojection683 can alternatively be positioned to extend from the bottom surface of theprimary member600.
• As shown inFIG. 33, theimplant device510 may include restraining means for restricting movement of one ormore bone fasteners550 coupled to thebase member520. The restraining means may be any means for securely covering at least a portion of at least onebone fastener550 so that thebone fastener550 is prevented from backing out of a bone body once screwed in. In the depicted embodiment, the bone screw restraining means includes a restrainingplate560 and a restraining plate fixing means570, such as a screw that can be configured to fit intohole670. As such, the restrainingplate560 could merely be a cover plate. The restrainingplate560 may be made of any suitable material known in the art, such as titanium or a titanium alloy, a radiolucent material, a radiopaque material, or combinations thereof. The restraining means does not have to be permanently fixed to the base member and may be removable. In the shown example, the restrainingplate560 is configured to correspond with a recessed region of thebase member520. The recessed region facilitates proper positioning of the restrainingplate560. The thickness of the restrainingplate560 should generally be as thin as possible, for example in the range from about 0.5 mm to about 2 mm. Alternative example embodiments of the restrainingplate560 and the way the embodiments interface with the bone fasteners are described herein. Also, the restriction of movement of one or more bone fasteners provided by restraining means may include control of relative motion (i.e., resistance to relative motion or changing resistance to relative motion) between one or bone fasteners and the base plate during subsidence. Still further, it is to be appreciated that within yet another example the restriction of movement as provided by restraining means may be considered to include both (1) bone fastener back-out prevention and (2) control of relative motion between one or bone fasteners and the base plate during subsidence.
• Additionally, it is to be appreciated that any other suitable bone screw restraining means can be used in connection with the present invention. For example, the bone screw restraining means can include multiple restraining plates that cover different bone screws. Alternatively, the bone screw restraining means can include one or more screws with heads that overlap at least a portion of one or more bone screws to thereby prevent the bone screws from backing out.
• In another embodiment, the peripherally-surroundedchamber692 formed by theprimary member600 can be divided into multiple interior compartments by interior members. Interior members can be composed or radiolucent or radiopaque materials. In order to increase radiographic evaluation of adjacent bone bodies and fusion material contained in each compartment of the peripherally-surroundedchamber692, the interior members are possibly composed of radiolucent material. The peripherally-surroundedchamber692 has a substantially flat inner face surface formed by theprimary member600. As illustrated, theinterface members530 can extend from the bottom surface of the peripherally-surroundedchamber692 in order to provide controlled subsidence with an adjacent bone body. Although not shown, the interface members can alternatively extend from the top surface of the peripherally-surroundedchamber692 or from both the top and bottom surfaces of thechamber692.
• As shown inFIG. 34, a centerinterior member694 can extend between the opposing inner surface faces of thechamber692 such that thechamber692 is divided into two or more compartments that can each hold or house fusion material to be placed between two adjacent bone bodies. As illustrated, theinterior member694 ofFIG. 34 extends from a portion of the inner face of the peripherally-surroundedchamber692 and is connected to an opposing inner face of thechamber692 orprimary member600. The addition of interior members, such asmember694, in the peripherally-surroundedchamber692 can add overall support and strength to theimplant device510. Interior members can further secure the fusion material between two bone bodies. It should be appreciated that one possible benefit associated with the presence of theinterior member694 is that it helps prevent PEEK implants from fracturing if they are impacted between the bones with excessive force.
• It is possible to load fusion material such as bone paste or bone chips into the peripherally-surroundedchamber692 prior to insertion of theimplant device510 between adjacent bone bodies (e.g., vertebrae). However, it may be easier to insert a chamber member having an open anterior face between adjacent bone bodies. In this case, the chamber member can then be packed with fusion material from the anterior face and then sealed off with a plate, such as thebase member520. Along this line, in order to ease the packing of the peripherally-surroundedchamber692 and the overall insertion of theimplant device510 into a patient, it may be desirable to detach thechamber member696 which forms a portion of the peripherally-surroundedchamber692 from theprimary member600. In accordance with another aspect of the present invention,FIG. 35 illustrates that theprimary member600 can include adetachable chamber member696 that encloses the open area or peripherally-surroundedchamber692 that is configured to receive fusion material. Theprimary member600 can further include afirst leg620 and asecond leg630 that form a curved open arc for receiving fusion material. As illustrated, the first andsecond legs620,630 of theprimary member600 can form generally a U-shape. The detachable function of thechamber member696 allows the U-shaped open area formed by the first andsecond legs620,630 of theprimary member600 and theU-shaped chamber member696 itself to be packed with fusion material separately before being subsequently implanted between two adjacent bone bodies.
• Thechamber member696 can be constructed from radiolucent material or radiopaque material. Because thechamber member696 can potentially limit radiographic evaluation of the fusion material and adjacent bone bodies, it may be desirable to construct thechamber member696 from radiolucent material. As shown, thechamber member696 has a U-shape. However, thechamber member696 can have any shape or be configured to match the shape of an adjacent bone body. When thechamber member696 is connected with the first andsecond legs620,630 of theprimary member600, the peripherally-surroundedchamber692, as shown, is generally rectangular. Although not shown, the peripherally-surroundedchamber692 can be circular or any other desirable shape depending on the configuration of thechamber member696 and first andsecond legs620,630. Thechamber member696 further has a top surface and a bottom surface that corresponds and aligns with the top650 and bottom651 surfaces of theprimary member600.
• As shown inFIG. 35, thechamber member696 can be connected to the first andsecond legs620,630 of theprimary member600 by a fastener, such as a screw or dowel, which can be inserted in the illustrated attachment holes710. The attachment holes710 extend through the first andsecond legs620,630 of theprimary member600 and are designed to be in register with the corresponding attachment holes710 in thechamber member696 when theimplant device510 is assembly such that thechamber member696 is attached or fastened to theprimary member600 in order to form the peripherally-surroundedchamber692. Theattachment face697 of the first andsecond legs620,630 is substantially flat such that it fits flush with theattachment face697 of thechamber member696. Thus, when the first andsecond legs620,630 are fastened to thechamber member696, the attachment faces697 are in register and thechamber member696 is tightly secured to theprimary member600.
• It is to be appreciated that the peripherally-surroundedchamber692 can be divided into more than one interior compartment if desired, such as that shown inFIG. 36, for example.FIG. 36 illustrates a U-shapeddetachable chamber member696 having aninterior member694 extending outwardly from the inner face of thechamber member696 in a direction parallel with the ends of thechamber member696 having the attachment faces697. Theprimary member600 andchamber member696 can be coupled together by any suitable structure or conventional means known in the art. As shown, theinterior member694 has anattachment face697 that is substantially flat. Theattachment face697 of theinterior member694 is designed to align and fit flush with a portion of the surface of theprimary member600. Although not shown, theattachment face697 of theinterior member694 can include a threaded fastener hole. Thehole670 could be configured differently, e.g., as a clearance hole, such that the restraining means can extend into the fastener hole of theinterior member694. In this case, the fastener used to attach the restraining means to thebase member520 can extend into theinterior member694 in order to secure thedetachable chamber member696 to theprimary member600. Similarly as shown inFIG. 35, the attachment faces697 of thechamber member696 and first andsecond legs620,630 can include attachment holes710 for fastening the two together. A screw, dowel or like fastener can be used to secure thechamber member696 to the first andsecond legs620,630 of theprimary member600.
• Thechamber member696 can be attached to theprimary member600 in a number of alternative methods. For example, in another embodiment,FIGS. 37 and 38 illustrate a peg and slot system that can be used to secure thechamber member696 to theprimary member600. The attachment faces697 of thechamber member696 can include apeg699 that corresponds to a slot (not shown) in the attachment faces697 of the first andsecond legs620,630 of theprimary member600. The slot is of like shape and has dimensions as that of thepeg699 so when fit together thepeg699 and slot are secured tightly. An adhesive that is conventional in the art can also be used to secure thepeg699 and slot together in order to ensure that thechamber member696 is securely attached to theprimary member600 of theimplant device510.
• In order to address the disadvantage that some radiolucent materials lack the strength of radiopaque materials, design modifications may be required to provide adequate structural integrity to theimplant device510. As illustrated inFIG. 39, the thickness of portions of theprimary member600 andsecondary member610, for example the bone screw holes640 andslot680 and portions surrounding the same, can be increased. Increasing the thickness of the bone screw holes640 and/orslots680 strengthens and adds support to the interface area between the bone screws550 that extend into a bone body and the primary and secondary members. Increasing the thickness of these portions likewise will increase the thread length or slot thickness. Designing portions of theimplant device510, such as theprimary member600 andsecondary member610, to be thicker or bulkier than other portions can mitigate the stresses of bone body migration and toggling of the bone screws the forces that may cause theimplant device510 to bend, crack or otherwise be damaged.
• It is to be appreciated that the implant device may include various other features. Some of these features may include features set forth within the patent applications identified herein and incorporated herein by reference. Some examples of the feature are shown inFIGS. 40-44. Some of the views are sectioned to show specific details. Such example feature may be utilized within any of the above mentioned embodiments. Of course, the shown features are merely examples and are not to be construed as limitations on the present invention.
• Turning toFIG. 40, as mentioned, the effective travel height (H) of theinterface members530 relates to a depth of penetration of the interface members into the bone body. However, the height (H) can also have an interrelationship with other relative movements that are associated with theimplant device510. For example, penetration of theinterface members530 into the bone body can be coordinated with pivoting and/or sliding of one or more bone screws relative to theirrespective holes640 andslots680 for controlled subsidence. As shown inFIG. 40, the bone screw associated with the slot can have a travel distance D. In one example concerning relative sliding within theslot680, as theinterface members530 reach a fully-embedded state, the screw will reach the at the end of theslot680. Such an example can be generally characterized by considering H to be equal to or approximately equal to D. Thus, the respective bone fastener is located within the slot so the screw travel matches penetration subsidence of the interface members into the bone body. Also the twoprojections683 extend upwardly from thetop surface650 of thebase member520 with aspace740 there between.
• Other examples concerning relative dimensioning are contemplated. Such other examples include relative sliding travel of the screw within theslot680 to end before theinterface members530 reach a fully-embedded state and relative sliding travel of the screw within theslot680 to still be permitted after theinterface members530 reach a fully-embedded state. Such examples can generally be characterized by considering H to be greater than D and by considering H to be less than D, respectively. Also, placement and sliding travel are possible variables. For example, the respective bone fastener can be placed to reach an end of the elongated slot and then toggle in the slot to permit the interface members to further penetrate into the bone body.
• FIG. 41 shows yet another example of another feature. Specifically, theinterface members532 could be located on the top surface. Thus, the location of the interface members is inverted. Another possible inversion relates to the holes and slots. Specifically,FIG. 42 shows the replacement of the holes (640,FIG. 41) with elongate slots642 (FIG. 42) and replacement of the elongate slot (680,FIG. 41) with a non-elongate hole582.
• Also, the above-mentioned modifications can be combined within various arrangements. For example,FIG. 43 shows thatonly slots642 and680 are provided. In other words, all holes are modified to slots. As another example,FIG. 44 shows thatinterface member530,532 can be located on both the bottom and top.FIG. 44 also shows the use ofonly slots642 and680. It is to be appreciated that such a combination ofinterface member530,532 andslots642,680 can provide for many types of subsidence control. The penetration of interface members and movement along slots can be configured and utilized in many different ways to provide different subsidence profiles. For example, subsidence could require more or less force and or time. Also, the subsidence may have different segments, each with a different profile.
• Also, another aspect that can affect the subsidence profile, theinterface members530,532 can be of any height or combination of heights. Thus, if a plurality ofinterface members530,532 extend from a surface of the base member, each interface member can be of equal heights or substantially taller or shorter than other interface members.FIG. 42 showsinterface members532 that have substantially dissimilar heights depending on the amount of subsidence resistance that is desired. Also, as compared to the interface members on the top and bottom, any relative dimensioning is possible. For example, the height of the interface members extending from the top surface may be greater, about the same, or less than height of the interface members extending from the bottom surface.
• Still further, it is contemplated that no relative sliding movement occurs between one, some or all of the plurality of fasteners and the base member during the controlled subsidence. This could be accomplished via use of only holes and no slots. In the alternative, a bone screw could be held against movement along a slot. For such a scenario, pivoting may occur and one of more of the bone screws.
• While shown embodiments of the present invention are described for supporting adjacent cervical vertebrae in the anterior region of the vertebrae, persons skilled in the art would recognize that the bone plate of the present invention may be utilized to support adjoining cervical, thoracic and lumbar in the region of the vertebral body. Further, the device and method of the invention is not limited to vertebral bodies, but can also be used to join two other pieces of bone in other parts of the body.
• While embodiments and applications of this invention have been shown and described, it would be apparent to those skilled in the art that many more modifications are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except in the spirit of the appended claim(s).

Claims (1)

What is claimed is:

1. An implant device for two adjacent vertebrae, the device including:

at least one portion configured for subsidence engagement with at least one of the vertebrae; and

at least portions that are configured for contacted relative movement during the subsidence engagement with at least one of the vertebrae.

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