US20050143737A1 - Dynamic spinal stabilization system - Google Patents

Abstract

A dynamic stabilization system includes a stabilization element, such as a spinal rod, a plurality of bone anchors, such as bone bolts, and a like plurality of connectors for connecting the bolts to the spinal rod. At least some of the connectors include a flexible element between the bone anchor and the rod and an adjustment element for adjusting the flexibility of the flexible element, to thereby adjust the dynamic flexibility between the rod and the bone anchor. In one embodiment, the flexible element is a flexible bearing element of a rod end bearing.

Description

• The present invention relates to spinal implant systems, and particularly to systems for stabilization of the spine. The invention provides a dynamic stabilization system that permits limited relative movement between the instrumented vertebrae and the stabilization system.
• In the past, the principal protocol for the treatment of the spine has been rigid fixation combined with fusion of the affected vertebral body or intervertebral disc. Arthrodesis, as this approach is known, has been achieved with a variety of rigid fixation elements, such as spinal rods or plates that are rigidly fixed to a vertebra using bone screws, bone bolts and spinal hooks. However, spinal fusion has been recognized to have limitations in the treatment of disc degeneration, especially in the earlier stages of the degeneration where it may be unnecessary to eliminate motion of the spinal motion segments.
• Clinical studies suggest that cells of the intervertebral disc respond favorably to reduced (but not eliminated) mechanical loading through deposition of extracellular matrix proteins (collagen, proteoglycan, fibronectin, etc.) into the disc space. In some cases, a degenerated disc may simply involve a mechanically overloaded and hypermobile segment that can be repaired by reversing the mechanically damaging load environment. For instance, clinical experiences with dynamic stabilization systems suggest that the disc becomes increasingly hydrated over time, as judged by MRI scanning.
• Spinal instability is a recognized effect of degenerative disc disease. In contrast to arthrodesis, arthroplasty is a protocol that contemplates restoring segmental spinal motion while treating the degenerative condition. Arthroplasty has been successfully used in the treatment of degenerative conditions of the hip and knee. In recent years, efforts have been made to implement arthroplasty in the spine, and most particularly in the intervertebral space. Intradiscal arthroplasty is now clinically available in the form of articulating prosthetic discs and polymeric disc nucleus replacements. With the availability of viable intradiscal arthroplasty devices, interest has grown in providing some means for dynamic spinal stabilization—i.e., stabilization that still permits some degree of mobility between spinal segments.
• Drawing from the approaches developed for intradiscal arthroplasty, efforts have made to develop an extradiscal arthroplasty. These systems offer the advantage of “soft stabilization” that limit, rather than eliminate, spinal segment motion. Current theories suggest that preventing movement of the spinal segments may not be a significant factor in clinical success of spinal stabilization systems. Instead, these theories focus on creating a normal loading pattern for the spine as a primary vehicle for successful spinal instrumentation. Thus, the goals for dynamic stabilization has been to restrict movement of the spine to a zone or range where normal or near normal loading of the spinal segments can occur. At the same time, dynamic stabilization techniques have sought to prevent the spine from adopting a position or orientation where abnormal loading of the spine can occur.
• One approach to achieve these goals for dynamic stabilization utilizes the spinous process. Thus, in one system, flexible “ligaments’ are engaged around the spinous process of adjacent vertebrae. Another form of flexible “ligament” is attached to the spinous process by way of small screws. In yet another approach, a polymeric spacer is held in place between the adjacent spinous processes. One system utilizes a coil spring that spans several vertebrae and that is anchored to the lamina of the end vertebrae. In one version, a rod extends through part of the coil spring to control rotation.
• Some dynamic stabilization systems have relied upon fixation to the pedicle of the vertebrae. In these types of systems, a pedicle screw is threaded into the pedicle of adjacent vertebrae. A member spans between the heads of the pedicle screws to limit the movement of the spinal segments. In one device, known as the Graf Ligament, a non-elastic band is wrapped around pedicle screw anchors. The non-elastic bands lock the spinal segment into lordosis, while permitting minimal rotation movements of the spine.
• Another system utilizing pedicle screws, provided by Sulzer Spine-Tech as the Dynesys System, incorporates a polymeric cylinder between the bone anchors. The Dynesys System permits, but limits, relative motion between adjacent vertebrae. The FASS System essentially integrates features from the Graf and Dynesys systems.
• The DSS System employs still another approach by including a spring element connected to pedicle screws. The spring element is contained within a polyurethane tube to prevent tissue ingrowth. Finally, some systems utilize a rigid member, such as a spinal plate, spanning between vertebrae. The flexible stabilization feature is incorporated into the interface between the pedicle screw and the rigid member, such as through a flexible washer or a spherical screw-plate interface.
• These prior extradiscal arthroplasty approaches all involve the introduction of flexible elements between spinal motion segments. Consequently, many of these systems are susceptible to over-loading the disc annulus or are, by necessity, unduly restrictive with respect to motion of the spinal segment.
• Moreover, these prior systems are not capable of altering the stiffness of a segment in various loading modes (e.g., flexion/extension, compression, lateral bending and axial rotation). Furthermore, these early approaches to arthrodesis do not allow selection of where, or at which motion segment, dynamic movement is permitted. Finally, no system exists that can readily convert to and from a soft stabilization to a more rigid or completely rigid system.
SUMMARY OF THE INVENTION
• In response to these limitations of the prior art, the present invention contemplates a dynamic stabilization system that relies upon flexible elements interposed between a bone anchor, such as a bone screw or spinal hook and a stabilization member, such as a rod or a plate. Furthermore, the present invention incorporates features that allow “fine tuning” of the dynamic flexibility of the total construct during the initial spinal instrumentation surgery, and even later during a revision procedure.
• In one embodiment of the invention, a dynamic stabilization system for stabilization of the spine comprises a stabilization element configured to span between at least two vertebrae of the spine, at least two bone anchors, each having a bone engagement portion, and at least two connectors for connecting a corresponding one of the bone anchors to the stabilization element. At least one of the connectors includes a flexible element between the bone anchor and the stabilization element to permit relative pivoting therebetween. In another embodiment, the connector also includes an adjustment element for adjusting the flexibility of the flexible element.
• In certain embodiments, the connector includes a bearing member attached to the stabilization element, in which the bearing member includes the flexible element. Where the stabilization element includes an elongated spinal rod, the bearing member is a rod end bearing including a rod engagement portion, and the flexible element is a bearing element of the rod end bearing. Where an adjustment element is provided, the bearing element is received within a bearing race of the rod end bearing and the adjustment element is arranged to compress the bearing element within the bearing race. The rod engagement portion includes a bore for receiving a portion of the spinal rod therein and a set screw for clamping the spinal rod within the bore.
• In another embodiment of the invention, at least one of the bone anchors of the stabilization system includes a stem having a threaded portion and the flexible element includes a bore for receiving the stem therethrough. In certain embodiments, the adjustment element includes a nut engaging the threaded portion and arranged to compress the flexible element as the nut is threaded onto the threaded portion.
• The dynamic stabilization system of the present invention can include come connectors that are configured to substantially rigidly connect one of the bone anchors to the stabilization element. Thus, the stabilization system can include a mix of rigid and flexible connectors that integrate the bone anchors to the stabilization element spanning the spine.
• In embodiments of the dynamic stabilization system in which the stabilization element is an elongated spinal rod, at least one of the bone anchors includes a stem having a threaded portion and defining slot sized to receive the spinal rod therethrough. The flexible element includes a sleeve disposed around the stem with at least a portion disposed between the bone engagement portion of the bone anchor and the spinal rod when the rod extends through the opening. Where an adjustment element is provided, it includes a nut engaging the threaded portion that is arranged to compress the sleeve as the nut is threaded onto the threaded portion. In certain embodiments, the flexible element includes a first sleeve disposed between the bone engagement portion and the spinal rod and a second sleeve disposed between the spinal rod and the nut. In other embodiments, the sleeve is disposed between the bone engagement portion and the nut and includes an opening for receiving rod therethrough when the rod extends through the slot in the stem.
• In embodiments of the dynamic stabilization system in which the stabilization element is an elongated spinal plate defining at least one opening therethrough, at least one of the bone anchors includes a stem having a threaded portion and the flexible element is a bushing engaged within the opening. The bushing defines a bore for receiving the stem therethrough and includes an upper head portion disposed between spinal plate and the nut. An adjustment element includes a nut engaging the threaded portion, whereby the nut compresses the head portion when the nut is threaded onto the threaded portion. In certain embodiments, the flexible element includes a lower head portion disposed between the spinal plate and the bone engaging portion of the bone anchor. The bone anchor further includes an intermediate portion between the bone engagement portion and the lower head portion of the bushing.
• The present invention contemplates a method for dynamic stabilization of motion segments of the spine comprising the steps of positioning a stabilization element adjacent the spine, the stabilization element configured to span a length of the spine between at least two motion segments, engaging bone anchors to at least two motion segments, and coupling the bone anchors to the stabilization element with a flexible element between at least one bone anchor and the stabilization element. The method further contemplates the step of adjusting the flexibility of the flexible element. This step of adjusting the flexibility includes compressing the flexible element. This method can be coupled with the step of repairing or replacing all or part of the intervertebral disc between at least two motion segments. In a more specific embodiment, the method is coupled with the replacement or augmentation of all or part of the nucleus pulposus with a polymeric prosthesis adapted to emulate the physical properties of the natural nucleus.
• In another aspect of the invention, a method for dynamic stabilization of a motion segment of the spine comprises the steps of introducing a device into an intervertebral space to at least partially maintain or restore the natural motion of the disc at the motion segment and then coupling a dynamic stabilization system across the motion segment that permits natural motion of the disc. The device can include a device for replacing or augmenting the nucleus pulposus of the intervertebral disc. In certain embodiments, the device includes a polymeric prosthesis configured to replace or augment the nucleus pulposus in which the polymeric prosthesis exhibits physical properties similar to the natural nucleus pulposus.
• It is one object to provide a system for the dynamic stabilization of the spine in which at least some of the natural motion of a spinal motion segment is retained. It is another object to provide a dynamic stabilization system that permits adjustment in the flexibility at different locations along the dynamic construct.
• One benefit of the present invention is that it can be readily adapted to existing stabilization constructs and can be integrated with known constructs that are fixed or that permit limited micro-motion. Another benefit is that the invention provides the orthopaedic surgeon with a great deal of flexibility in the initial surgical procedure or in a subsequent revision procedure.
• Other objects and benefits of the invention can be discerned from the following written description taken along with the accompanying figures.
DESCRIPTION OF THE DRAWINGS
• FIG. 1 is an anterior view of a human spine instrumented with a stabilization construct.
• FIG. 2 is a side view of a connector capable of providing dynamic fixation within the stabilization construct shown inFIG. 1.
• FIG. 3 is a top view of a flexible bearing component of the connector illustrated inFIG. 2.
• FIG. 4 is a perspective view of an alternative bearing element for use in a flexible bearing component of the type depicted inFIG. 3.
• FIG. 5 is a side view of a connector according to a further embodiment of the invention for providing dynamic fixation within the stabilization construct shown inFIG. 1.
• FIG. 6 is a side partial view of the connector shown inFIG. 5.
• FIG. 7 is a perspective view of an elastomeric sleeve for use with theconnector50 shown inFIG. 5.
• FIG. 8 is a perspective view of a stabilization plate for use in a dynamic spinal stabilization construct.
• FIG. 9 is a cross-sectional view of the stabilization plate shown inFIG. 7, taken along line9-9 as viewed in the direction of the arrows.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
• For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains.
• An exemplary spinal construct is depicted inFIG. 1. In this construct, a scaffolding is affixed to opposite sides of the spine. In the illustrated configuration, a pair of stabilization elements, in the form of spinal rods R, span from the L3 vertebra, across the L4 and L5 vertebrae and ending at the sacrum S. A series of connectors C1-C4 fasten the rod R to the vertebrae. The connectors in a typical stabilization construct include some form of anchor element, such as a bone screw or a spinal hook. In recent years, the pedicle screw has become a bone anchor of choice.
• In prior stabilization constructs, the connectors and associated bone anchors have been common at each instrumented vertebral level. In the typical case, the stabilization element, such as rod R, was rigidly fixed to the bone anchor, or at best was permitted some “micro-motion”. In accordance with one feature of the present invention, the connectors C1-C4 can be different—e.g., they can provide different levels of flexibility or rigidity depending upon the physiological requirements for the particular patient and the nature of the injury or damage to the spine that is being addressed by the stabilization construct.
• Connectors and bone anchors for a generally rigid fixation are well known. Connectors providing dynamic stabilization may be constructed in accordance with the embodiments disclosed herein. For instance, in one embodiment, aconnector10, depicted inFIG. 2, includes abone anchor12 that is in the form of a bone screw withbone engaging threads13. Thebone anchor12 includes anintermediate platform15 from which projects apost16. Thepost16 includes a non-threaded portion17 and terminate in a threadedportion18. The threadedportion18 preferably carries machine threads for engaging a threadednut20. As thus far described, the bone anchor is constructed similar to the bone screw described and illustrated in U.S. Pat. No. 4,836,196 to Park et al., the disclosure of which is incorporated herein by reference. It is understood that thepost16 can include an internal or an external driving feature (not shown) for engagement by a tool to thread thebone threads13 into a vertebra. It is also contemplated that a locking nut is provided that can lock the position ofnut20 on thebone anchor12.
• Thebone anchor12 is engaged to the stabilization element R by way of a bearingmember25. The bearing member is similar to a rod-end bearing used in industrial machinery applications. For example, the bearingmember25 can be similar to the HME self-lubricating rod end manufactured by Heim Bearings of Fairfield, Conn. The bearingmember25 includes a bearingelement27 that defines apassageway28 to receive thestem16 of thebone anchor12, as shown inFIG. 2. The bearing element is slidably disposed within a bearingrace29 so that the bearingelement27 articulates within the race in its permitted degrees of freedom.
• Therace29 is mounted within abore34 defined in a bearinghousing31. The race is fixed within the housing in a conventional manner, such as by a press-fit engagement. As shown inFIGS. 2-3, thehousing31 generally conforms to the shape of the bearingelement27—in this case the bearing element is spherical so the housing is circular. The housing defines at least onerod engagement element32. When theconnector10 is situated at the end of a construct, such as the connector C1 inFIG. 1, only one engagement element is necessary. However, if theconnector10 is situated within the length of the construct, such as the connectors C2 or C3, then a secondrod engagement element36 can be provided on thehousing31.
• Therod engagement element32 is configured for attachment or connection to the stabilization rod R. Thus, in its simplest form, theelement32 is welded to the rod end. Preferably, theengagement element32 defines abore33 for snugly receiving the rod end. Alternatively, theelement32 can define a press-fit engagement with the rod end. Thebore33 and the rod end can define complementary non-circular features to prevent rotation of the rod about its axis within therod engagement element32.
• Most preferably, some additional fixation is provided to positively and solidly engage the bearing housing to the rod R. Thus, as shown with respect to therod engagement element36, the rod bore37 is intersected by aset screw40, which is configured as is typical for spinal implants. The set screw can be threaded into theengagement element37 to bear against the rod end to clamp the bearinghousing31 to the rod R.Several set screws40 are provided to ensure a solid fixation between the two parts.
• As shown inFIG. 2, thestem16 of thebone anchor12 extends through thebore28 in thebearing element27. The bearing element is sandwiched between theintermediate portion15 of the bone anchor and thenut20. Alternatively, aspacer22 may be interposed between theintermediate portion15 and the bearingelement27. Thespacer22 can be utilized where necessary to accommodate height differences between the rod and the vertebrae along the length of the rod R.
• In accordance with the present invention, the bearingmember25 allows articulation of the rod R andbone anchor12 relative to each other in certain degrees of freedom. For instance, thestem16 of the bone anchor can move in the direction of the arrows inFIG. 2 when subjected to the loads applied to the threadedportion13 of the anchor that is engaged within a vertebra. The present invention contemplates aconnector10 that allows adjustment of the relative flexibility of this articulating bearing joint. Thus, in one specific embodiment, at least oneset screw42 is threaded into thehousing31 to engage thebearing element29, as shown inFIG. 3. In this specific embodiment, the bearingelement29 is fixed to thehousing31, thereby producing an essentially rigid connection between thebone anchor12 and the stabilization rod R.
• In another embodiment, the degree of flexibility is adjusted by the amount of compression of the bearingelement27. In this embodiment, the bearing element is formed of an elastomeric material that is compressed between theintermediate portion15 and thenut20. As the nut is tightened onto the threadedend18 of thestem16, it presses the bearingelement27 which causes it to bulge transverse to the compressive force. As the bearing element bulges, it presses outward into therace29, thereby increasing the frictional resistance between the two components. Thus, thenut20 operates as an adjustment element to adjust the dynamic flexibility of the bearing element.
• It can be appreciated that this flexibility adjustment can occur at any time during the life of the stabilization construct. In other words, the construct can be initially implanted with a particular degree of flexibility in theconnector10 at any instrumented vertebral level. Moreover, if it is later determined that this degree of flexibility requires adjustment, minimally invasive procedures can be used to access thenut20 and either tighten or loosen the nut depending upon whether theconnector10 needs less or more flexibility.
• It is understood that the elements of the connector must be formed of medical grade materials, and especially of materials that can withstand the extreme loads experienced by the spinal construct. Thus, thebone anchor12,nut20 and bearinghousing31 may be formed of a biocompatible metal, such as stainless steel or titanium. The bearingrace29 can also be formed of a biocompatible metal, provided that its surface is polished to provide a sufficient articulating surface for the bearing element. Preferably, the bearingrace29 is formed of a biocompatible polymer, including UHMWPE, PTFE, nylon, polyurethane, or thermoplastic elastomers, such as HYTRL™. The bearingelement27 may be formed of the same material as the bearing race. Alternatively, the bearing element may be formed of a material that is more elastic than the material of the bearing race.
• In the embodiment illustrated inFIG. 2, the bearingelement27 is spherical and therace29 defines a articulating surface. Thus, with this embodiment, the connector nominally permits relative movement between the rod R and the bone anchor12 (and consequently the instrumented vertebra) in several degrees of freedom and in several planes that intersect the plane of the rod and bone anchor. Thus, while the pivot arrows inFIG. 2 reside in the rod/bone anchor plane, the bone anchor can also pivot along transverse planes projecting out of the paper. In many stabilization constructs, the dynamic stabilization is limited to specific planes or degrees of freedom, and most particularly to the rod/bone anchor plane (i.e., the plane of the paper inFIG. 2).
• In order to control the degree of freedom of theconnector10, theset screws42 can be replaced with pivot pins that fit within corresponding bores (not shown) formed in thebearing element27. Alternatively, the bearing element can assume different configurations, such as theoblong element45 shown inFIG. 4. Theelement45 defines acentral bore48 for receiving thestem16 of thebone anchor12. This oblong bearing element includes generallylinear sides46 bounded by generally spherically shaped ends47. The bearing race can be configured accordingly to receive theoblong bearing element45. The generallylinear sides46 prevent pivoting relative to those surfaces, while the spherical ends47 permit pivoting in that corresponding plane. The bearingelement45 exhibits the same compressive properties as theelement27 discussed above to permit adjustment of the flexibility of the bearing joint.
• In one feature of the invention, the interface between the bone anchor and the stabilization element is adjustable, either during or subsequent to the initial surgery in which the stabilization scaffolding is implanted. This feature is accomplished by the use of elastomeric elements that can be compressed to adjust their dynamic flexibility. This feature is implemented in an additional embodiment of the present invention depicted inFIGS. 5 and 6. In this embodiment, aconnector50 includes abone anchor52 that includesbone engaging threads53, anintermediate portion55 and astem56 having anon-threaded portion57 and a threadedend59. Anut60 is also provided for engaging the threaded end of the stem. Thebone anchor52 is thus far similar to theanchor12 described above.
• However, with this embodiment, thenon-threaded portion57 of thestem56 defines avertical slot58 configured to receive the stabilization rod R therethrough. Preferably, the width of the slot is close to the outer diameter of the rod, while the vertical height of the slot is greater than the diameter. As can be seen in the figures, the rod R passes through thevertical slot58 and is sandwiched betweenopposite sleeves65_Uand65_L. Both sleeves are preferably formed of an elastomeric material that is resiliently compressed as thebone anchor52 pivots in the direction indicated by the arrows inFIG. 5. Thesleeves65 define abore66 through which thestem56 of thebone anchor52 extends.
• As with the previous embodiment, thenut60 is used to change the dynamic flexibility of theconnector50 by adjusting the amount that theresilient sleeves65 are compressed. A washer (not shown) is provided between thenut60 and theuppermost sleeve65_Uso that tightening the nut does not compromise the integrity of the sleeve. The dynamic flexibility of theconnector50 may also be adjusted by using sleeves having different thicknesses or different elastomeric material properties. Theelongated slot58 may be sized to accommodate an expected range of thicknesses of thelowermost sleeve65_L.
• In the embodiment shown inFIGS. 5 and 6, upper andlower sleeves65_U,65_Lare provided. In an alternative embodiment, asingle sleeve70 may be utilized, as shown inFIG. 7. The sleeve defines abore72 that is sized to receive thestem56 of thebone anchor52. Thesleeve70 further defines atransverse bore74 that is sized to receive the stabilization rod R. Thesleeve70 can be compressed by thenut60 to adjust the dynamic flexibility of the connector, in the manner described above.
• Adjustability of dynamic flexibility of a stabilization construct may also be implemented in a system that relies upon an elongated stabilization plate. In particular, astabilization plate80, as shown inFIGS. 8-9, is provided with a plurality ofopenings83 for engagement with a plurality of bone anchors, such as theanchor52 depicted in phantom lines inFIG. 9. The stabilization plate is sized to span several vertebral levels, with theopenings83 spaced accordingly. The openings in theplate80 may be individual bores or may be in the form of elongated slots, similar to the slotted spinal plate disclosed in U.S. Pat. No. 4,836,196, the disclosure of which has been incorporated by reference.
• In order to provide the dynamic flexibility feature of the present invention, theplate80 includes a plurality ofelastomeric bushings85 that are pressed into a corresponding one of theopenings83. As shown inFIG. 9, thebushings85 include acentral collar84 that is sized to fit within anopening83, preferably snugly. The collar defines abore91 for receiving thestem56 of theanchor52 therethrough. The collar terminates at its ends in upper andlower head portions87_U,87_Lthat are larger than theopenings83 in theplate80 to trap thebushing85 within the opening.
• Thelower head portion87_Lis supported on theintermediate portion55 of the anchor, which thenut60 bears against theupper head portion87_U. The twohead portions87 are compressed by tightening thenut60 onto thestem56 of thebone anchor52, to thereby increase the rigidity (or decrease the dynamic flexibility) of the plate-to-bone anchor interface.
• The dynamic stabilization system of the present invention is well suited as an adjunct to a disc repair procedure. For instance, an intervertebral disc may require augmentation or replacement, depending upon the severity of the damage or disease to the disc. Where the disc is intact, it is important to maintain the loading pattern as normal as possible since this loading pattern helps hydrate the disc and flush toxins from the disc. The dynamic stabilization systems disclosed herein provide stabilization for the affected disc while allowing a meaningful amount of motion at that vertebral level.
• Devices have been developed for replacement of the intervertebral disc. In some cases, the device is a mechanical device that is configured to mimic the mechanics of the disc motion. In more recent years, the nucleus pulposus of the intervertebral disc has been replaced with a polymer prosthesis that emulates the physical and chemical properties of the disc. In particular, these types of prostheses are intended to preserve or restore the movement and load response of the affected disc as close to the natural disc as possible. One such material is a hydrogel that has similar elastic properties to the natural nucleus pulposus and that shares a similar fluid transport mechanism to the natural disc. This material can be used to replace the entire nucleus pulposus, or to augment the existing nucleus where voids or other defects in the nucleus exist.
• Even where the intervertebral disc has been replaced with a mechanical device, or where all or part of the nucleus pulposus has been replaced or augmented by a polymer prosthesis, restoration and maintenance of normal spinal segment motion is important. Consequently, it is contemplated that the dynamic stabilization system of the present invention, includingconnectors10,50 or theplate80, may be used in connection with disc/nucleus repair or replacement procedures.
• Thus, in one aspect of the invention, a method for dynamic stabilization of a motion segment includes the step of introducing a device into an intervertebral space that at least partially restore or maintain the natural motion of the intervertebral disc. The motion segment is instrumented with a dynamic stabilization system that includes one or more of theconnectors10,50 or theplate80, which permits the natural motion of the disc.
• While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the invention are desired to be protected.

Claims (30)

1. A dynamic stabilization system for stabilization of the spine, comprising:

a stabilization element configured to span between at least two vertebrae of the spine:

at least two bone anchors, each having a bone engagement portion; and

at least two connectors for connecting a corresponding one of said bone anchors to said stabilization element, at least one connector including;

a flexible element between the bone anchor and the stabilization element to permit relative pivoting therebetween; and

an adjustment element for adjusting the flexibility of said flexible element.

2. The dynamic stabilization system according toclaim 1, wherein said at least one connector includes a bearing member attached to said stabilization element, said bearing member including said flexible element.

3. The dynamic stabilization system according toclaim 2, wherein:

said stabilization element includes an elongated spinal rod;

said bearing member is a rod end bearing including a rod engagement portion;

and said flexible element is a bearing element of said rod end bearing.

4. The dynamic stabilization system according toclaim 3, wherein:

said bearing element is received within a bearing race of said rod end bearing; and

said adjustment element is arranged to compress said bearing element within said bearing race.

5. The dynamic stabilization system according toclaim 3, wherein said rod engagement portion includes a bore for receiving a portion of said spinal rod therein and a set screw for clamping said spinal rod within said bore.

6. The dynamic stabilization system according toclaim 1, wherein:

at least one of said bone anchors includes a stem having a threaded portion;

said flexible element includes a bore for receiving said stem therethrough; and

said adjustment element includes a nut engaging said threaded portion and arranged to compress said flexible element as said nut is threaded onto said threaded portion.

7. The dynamic stabilization system according toclaim 6, wherein said at least one of said bone anchors includes an intermediate portion between said stem and said bone engagement portion, said intermediate portion configured to support said flexible element so that said flexible element is compressed between said intermediate portion and said nut when said nut is threaded onto said threaded portion.

8. The dynamic stabilization system according toclaim 1, wherein another of said connectors is configured to substantially rigidly connect one of said bone anchors to said stabilization element.

9. The dynamic stabilization system according toclaim 1, wherein:

said stabilization element includes an elongated spinal rod;

at least one of said bone anchors includes a stem having a threaded portion and defining slot sized to receive said spinal rod therethrough;

said flexible element includes a sleeve disposed around said stem with at least a portion disposed between the bone engagement portion of the bone anchor and the spinal rod when the rod extends through said opening; and

said adjustment element includes a nut engaging said threaded portion and arranged to compress said sleeve as said nut is threaded onto said threaded portion.

10. The dynamic stabilization system according toclaim 9, wherein said flexible element includes a first sleeve disposed between said bone engagement portion and the spinal rod and a second sleeve disposed between said spinal rod and said nut.

11. The dynamic stabilization system according toclaim 9, wherein said sleeve is disposed between said bone engagement portion and said nut and includes an opening for receiving rod therethrough when said rod extends through said slot in said stem.

12. The dynamic stabilization system according toclaim 1, wherein:

said stabilization element is an elongated spinal plate defining at least one opening therethrough;

at least one of said bone anchors includes a stem having a threaded portion;

said adjustment element includes a nut engaging said threaded portion; and

said flexible element is a bushing engaged within said at least one opening, said bushing defining a bore for receiving said stem therethrough and including an upper head portion disposed between spinal plate and said nut, whereby said nut compresses said head portion when said nut is threaded onto said threaded portion.

13. The dynamic stabilization system according toclaim 12, wherein said flexible element includes a lower head portion disposed between said spinal plate and said bone engaging portion of said bone anchor.

14. The dynamic stabilization system according toclaim 13, wherein said bone anchor includes an intermediate portion between said bone engagement portion and said lower head portion of said bushing.

15. A dynamic stabilization system for stabilization of the spine, comprising:

a stabilization element configured to span between at least two vertebrae of the spine:

at least two bone anchors, each having a bone engagement portion and a stem portion; and

at least two connectors for connecting a corresponding one of said bone anchors to said stabilization element, at least one connector including a bearing member associated with said stabilization element and including bearing race and a flexible bearing element mounted within said bearing race, said flexible bearing element configured to receive said stem portion of said bone anchor therethrough.

16. The dynamic stabilization system according toclaim 15 wherein said at least one connector includes an adjustment element for adjusting the flexibility of said flexible bearing element.

17. The dynamic stabilization system according toclaim 16, wherein said adjustment element is arranged to compress said bearing element within said bearing race.

18. The dynamic stabilization system according toclaim 17, wherein:

said stem of least one of said bone anchors includes a threaded portion; and

said adjustment element includes a nut engaging said threaded portion and arranged to compress said flexible bearing element as said nut is threaded onto said threaded portion.

19. The dynamic stabilization system according toclaim 15, wherein:

said stabilization element includes an elongated spinal rod;

said bearing member is a rod end bearing including a rod engagement portion configured for engagement to said spinal rod.

20. The dynamic stabilization system according toclaim 19, wherein said rod engagement portion includes a bore for receiving a portion of said spinal rod therein and a set screw for clamping said spinal rod within said bore.

21. A dynamic stabilization system for stabilization of the spine, comprising:

an elongated spinal stabilization rod configured to span between at least two vertebrae of the spine:

at least two bone anchors, each having a bone engagement portion and at least one of said bone anchors including a stem defining slot sized to receive said spinal rod therethrough; and

a flexible sleeve disposed around said stem with at least a portion disposed between the bone engagement portion of the bone anchor and the spinal rod when the rod extends through said opening.

22. The dynamic stabilization system according toclaim 21, wherein:

said stem includes a threaded portion, and

said system further comprises a nut engaging said threaded portion and arranged to compress said sleeve as said nut is threaded onto said threaded portion.

23. The dynamic stabilization system according toclaim 22, wherein said flexible sleeve includes a first sleeve disposed between said bone engagement portion and the spinal rod and a second sleeve disposed between said spinal rod and said nut.

24. The dynamic stabilization system according toclaim 23, wherein said flexible sleeve is disposed between said bone engagement portion and said nut and includes an opening for receiving rod therethrough when said rod extends through said slot in said stem.

25. A method for dynamic stabilization of motion segments of the spine comprising the steps of:

positioning a stabilization element adjacent the spine, the stabilization element configured to span a length of the spine between at least two motion segments;

engaging bone anchors to at least two motion segments;

coupling the bone anchors to the stabilization element with a flexible element between at least one bone anchor and the stabilization element; and

adjusting the flexibility of said flexible element.

26. The method for dynamic stabilization according toclaim 25, wherein the step of adjusting the flexibility includes compressing said flexible element.

27. The method for dynamic stabilization according toclaim 25, further comprising the step of repairing or replacing all or part of the intervertebral disc between at least two motion segments.

28. A method for dynamic stabilization of a motion segment of the spine comprising the steps of:

introducing a device into an intervertebral space to at least partially maintain or restore the natural motion of the disc at the motion segment; and

coupling a dynamic stabilization system across the motion segment that permits natural motion of the disc.

29. The method for dynamic stabilization according toclaim 28, wherein the device includes a device for replacing or augmenting the nucleus pulposus of the intervertebral disc.

30. The method for dynamic stabilization according toclaim 29, wherein the step of introducing a device includes introducing a polymeric prosthesis to replace or augment the nucleus pulposus in which the polymeric prosthesis exhibits physical properties similar to the natural nucleus pulposus

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