US20110106167A1 - Adjustable spinal stabilization system - Google Patents

Abstract

An adjustable spinal stabilization system having a flexible connection unit for non-rigid stabilization of the spinal column. In one embodiment, the spinal stabilization system includes a flexible connection unit having a tether running through a hollow portion of the flexible connection unit, wherein the tether limits bending of the flexible connection unit. In a further embodiment the tether is pre-tensioned. In a further embodiment, the tension upon or compression of the tether is adjustable.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• The present application is a continuation-in-part of U.S. patent application Ser. No. 10/798,014, filed Mar. 10, 2004, entitled “A Method and Apparatus for Flexible Fixation of a Spine” which is a continuation-in-part of U.S. patent application Ser. No. 10/728,566, filed on Dec. 5, 2003.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The present invention relates to a method and system for stabilizing a spinal column and, more particularly, to a method and system of spinal fixation in which one or more screw type securing members are implanted and fixed into a portion of a patient's spinal column and a longitudinal member including flexible, semi-rigid rod-like or plate-like structures of various cross-sections (hereinafter referred to as “rods” or “plates”, respectively) are connected and fixed to the upper ends of the securing members to provide stabilization of the spinal column.
• 2. Description of the Related Art
• Degenerative spinal column diseases, such as disc degenerative diseases (DDD), spinal stenosis, spondylolisthesis, and so on, need surgical operation if they do not take a turn for the better by conservative management. Typically, spinal decompression is the first surgical procedure that is performed. The primary purpose of decompression is to reduce pressure in the spinal canal and on nerve roots located therein by removing a certain tissue of the spinal column to reduce or eliminate the pressure and pain caused by the pressure. If the tissue of the spinal column is removed the pain is reduced but the spinal column is weakened. Therefore, fusion surgery (e.g., ALIF, PLIF or posterolateral fusion) is often necessary for spinal stability following the decompression procedure. However, following the surgical procedure, fusion takes additional time to achieve maximum stability and a spinal fixation device is typically used to support the spinal column until a desired level of fusion is achieved. Depending on a patient's particular circumstances and condition, a spinal fixation surgery can sometimes be performed immediately following decompression, without performing the fusion procedure. The fixation surgery is performed in most cases because it provides immediate postoperative stability and, if fusion surgery has also been performed, it provides support of the spine until sufficient fusion and stability has been achieved.
• Conventional methods of spinal fixation utilize a rigid spinal fixation device to support an injured spinal part and prevent movement of the injured part. These conventional spinal fixation devices include: fixing screws configured to be inserted into the spinal pedicle or sacral of the backbone to a predetermined depth and angle, rods or plates configured to be positioned adjacent to the injured spinal part, and coupling elements for connecting and coupling the rods or plates to the fixing screws such that the injured spinal part is supported and held in a relatively fixed position by the rods or plates.
• U.S. Pat. No. 6,193,720 discloses a conventional spinal fixation device, in which connection members of a rod or plate type are mounted on the upper ends of at least one or more screws inserted into the spinal pedicle or sacral of the backbone. The connection units, such as the rods and plates, are used to stabilize the injured part of the spinal column which has been weakened by decompression. The connection units also prevent further pain and injury to the patient by substantially restraining the movement of the spinal column. However, because the connection units prevent normal movement of the spinal column, after prolonged use, the spinal fixation device can cause ill effects, such as “junctional syndrome” (transitional syndrome) or “fusion disease” resulting in further complications and abnormalities associated with the spinal column. In particular, due to the high rigidity of the rods or plates used in conventional fixation devices, the patient's fixed joints are not allowed to move after the surgical operation, and the movement of the spinal joints located above or under the operated area is increased. Consequently, such spinal fixation devices cause decreased mobility of the patient and increased stress and instability to the spinal column joints adjacent to the operated area.
• It has been reported that excessive rigid spinal fixation is not helpful to the fusion process due to load shielding caused by rigid fixation. Thus, trials using load sharing semi-rigid spinal fixation devices have been performed to eliminate this problem and assist the bone fusion process. For example, U.S. Pat. No. 5,672,175, U.S. Pat. No. 5,540,688, and U.S. Pub No 2001/0037111 disclose dynamic spine stabilization devices having flexible designs that permit axial load translation (i.e., along the vertical axis of the spine) for bone fusion promotion. However, because these devices are intended for use following a bone fusion procedure, they are not well-suited for spinal fixation without fusion. Thus, in the end result, these devices do not prevent the problem of rigid fixation resulting from fusion.
• To solve the above-described problems associated with rigid fixation, non-fusion technologies have been developed. The Graf band is one example of a non-fusion fixation device that is applied after decompression without bone fusion. The Graf band is composed of a polyethylene band and pedicle screws to couple the polyethylene band to the spinal vertebrae requiring stabilization. The primary purpose of the Graf band is to prevent sagittal rotation (flexion instability) of the injured spinal parts. Thus, it is effective in selected cases but is not appropriate for cases that require greater stability and fixation. See, Kanayama et al, Journal of Neurosurgery 95(1 Suppl):5-10, 2001, Markwalder & Wenger, Acta Neurochrgica 145(3):209-14.). Another non-fusion fixation device called “Dynesys” has recently been introduced. See Stoll et al, European Spine Journal 11 Suppl 2:S170-8, 2002, Schmoelz et. al., J. of Spinal Disorder & Techniques 16(4):418-23, 2003. The Dynesys device is similar to the Graf band except it uses a polycarburethane spacer between the screws to maintain the distance between the heads of two corresponding pedicle screws and, hence, adjacent vertebrae in which the screws are fixed. Early reports by the inventors of the Dynesys device indicate it has been successful in many cases. However, it has not yet been determined whether the Dynesys device can maintain long-term stability with flexibility and durability in a controlled study. Because it has polyethylene components and interfaces, there is a risk of mechanical failure. Furthermore, due to the mechanical configuration of the device, the surgical technique required to attach the device to the spinal column is complex and complicated.
• U.S. Pat. Nos. 5,282,863 and 4,748,260 disclose a flexible spinal stabilization system and method using a plastic, non-metallic rod. U.S. patent publication no. 2003/0083657 discloses another example of a flexible spinal stabilization device that uses a flexible elongate member. These devices are flexible but they are not well-suited for enduring long-term axial loading and stress. Additionally, the degree of desired flexibility vs. rigidity may vary from patient to patient. The design of existing flexible fixation devices are not well suited to provide varying levels of flexibility to provide optimum results for each individual candidate. For example, U.S. Pat. No. 5,672,175 discloses a flexible spinal fixation device which utilizes a flexible rod made of metal alloy and/or a composite material. Additionally, compression or extension springs are coiled around the rod for the purpose of providing de-rotation forces on the vertebrae in a desired direction. However, this patent is primarily concerned with providing a spinal fixation device that permits “relative longitudinal translational sliding movement along [the] vertical axis” of the spine and neither teaches nor suggests any particular designs of connection units (e.g., rods or plates) that can provide various flexibility characteristics. Prior flexible rods such as that mentioned in U.S. Pat. No. 5,672,175 typically have solid construction with a relatively small diameter in order to provide a desired level of flexibility. Because they are typically very thin to provide suitable flexibility, such prior art rods are prone to mechanical failure and have been known to break after implantation in patients.
• Therefore, conventional spinal fixation devices have not provided a comprehensive and balanced solution to the problems associated with curing spinal diseases. Many of the prior devices are characterized by excessive rigidity, which leads to the problems discussed above while others, though providing some flexibility, are not well-adapted to provide varying degrees of flexibility. Therefore, there is a need for an improved dynamic spinal fixation device that provides a desired level of flexibility to the injured parts of the spinal column, while also providing long-term durability and consistent stabilization of the spinal column.
• Additionally, in a conventional surgical method for fixing the spinal fixation device to the spinal column, a doctor incises the midline of the back to about 10-15 centimeters, and then, dissects and retracts it to both sides. In this way, the doctor performs muscular dissection to expose the outer part of the facet joint. Next, after the dissection, the doctor finds an entrance point to the spinal pedicle using radiographic devices (e.g., C-arm flouroscopy), and inserts securing members of the spinal fixation device (referred to as “spinal pedicle screws”) into the spinal pedicle. Thereafter, the connection units (e.g., rods or plates) are attached to the upper portions of the pedicle screws in order to provide support and stability to the injured portion of the spinal column. Thus, in conventional spinal fixation procedures, the patient's back is incised about 10˜15 cm, and as a result, the back muscle, which is important for maintaining the spinal column, is incised or injured, resulting in significant post-operative pain to the patient and a slow recovery period.
• Recently, to reduce patient trauma, a minimally invasive surgical procedure has been developed which is capable of performing spinal fixation surgery through a relatively small hole or “window” that is created in the patient's back at the location of the surgical procedure. Through the use of an endoscope, or microscope, minimally invasive surgery allows a much smaller incision of the patient's affected area. Through this smaller incision, two or more securing members (e.g., pedicle screws) of the spinal fixation device are screwed into respective spinal pedicle areas using a navigation system. Thereafter, special tools are used to connect the stabilizing members (e.g., rods or plates) of the fixation device to the securing members. Alternatively, or additionally, the surgical procedure may include inserting a step dilator into the incision and then gradually increasing the diameter of the dilator. Thereafter, a tubular retractor is inserted into the dilated area to retract the patient's muscle and provide a visual field for surgery. After establishing this visual field, decompression and, if desired, fusion procedures may be performed, followed by a fixation procedure, which includes the steps of finding the position of the spinal pedicle, inserting pedicle screws into the spinal pedicle, using an endoscope or a microscope, and securing the stabilization members (e.g., rods or plates) to the pedicle screws in order to stabilize and support the weakened spinal column.
• One of the most challenging aspects of performing the minimally invasive spinal fixation procedure is locating the entry point for the pedicle screw under endoscopic or microscopic visualization. Usually anatomical landmarks and/or radiographic devices are used to find the entry point, but clear anatomical relationships are often difficult to identify due to the confined working space. Additionally, the minimally invasive procedure requires that a significant amount of the soft tissue must be removed to reveal the anatomy of the regions for pedicle screw insertion. The removal of this soft tissue results in bleeding in the affected area, thereby adding to the difficulty of finding the correct position to insert the securing members and causing damage to the muscles and soft tissue surrounding the surgical area. Furthermore, because it is difficult to accurately locate the point of insertion for the securing members, conventional procedures are unnecessarily traumatic.
• Radiography techniques have been proposed and implemented in an attempt to more accurately and quickly find the position of the spinal pedicle in which the securing members will be inserted. However, it is often difficult to obtain clear images required for finding the corresponding position of the spinal pedicle using radiography techniques due to radiographic interference caused by metallic tools and equipment used during the surgical operation. Moreover, reading and interpreting radiographic images is a complex task requiring significant training and expertise. Radiography poses a further problem in that the patient is exposed to significant amounts of radiation.
• Although some guidance systems have been developed which guide the insertion of a pedicle screw to the desired entry point on the spinal pedicle, these prior systems have proven difficult to use and, furthermore, hinder the operation procedure. For example, prior guidance systems for pedicle screw insertion utilize a long wire that is inserted through a guide tube that is inserted through a patient's back muscle and tissue. The location of insertion of the guide tube is determined by radiographic means (e.g., C-arm fluoroscope) and driven until a first end of the guide tube reaches the desired location on the surface of the pedicle bone. Thereafter, a first end of the guide wire, typically made of a biocompatible metal material, is inserted into the guide tube and pushed into the pedicle bone, while the opposite end of the wire remains protruding out of the patient's back. After the guide wire has been fixed into the pedicle bone, the guide tube is removed, and a hole centered around the guide wire is dilated and retracted. Finally, a pedicle screw having an axial hole or channel configured to receive the guide wire therethrough is guided by the guide wire to the desired location on the pedicle bone, where the pedicle screw is screw-driven into the pedicle.
• Although the concept of the wire guidance system is a good one, in practice, the guide wire has been very difficult to use. Because it is a relatively long and thin wire, the structural integrity of the guide wire often fails during attempts to drive one end of the wire into the pedicle bone, making the process unnecessarily time-consuming and laborious. Furthermore, because the wire bends and crimps during insertion, it does not provide a smooth and secure anchor for guiding subsequent tooling and pedicle screws to the entry point on the pedicle. Furthermore, current percutaneous wire guiding systems are used in conjunction with C-arm flouroscopy (or other radiographic device) without direct visualization with t he use of an endoscope or microscope. Thus, current wire guidance systems pose a pot ential risk of misplacement or pedicle breakage. Finally, because one end of the wire remains protruding out of the head of the pedicle screw, and the patient's back, this wire hinders freedom of motion by the surgeon in performing the various subsequent procedures involved in spinal fixation surgery. Thus, there is a need to provide an improved guidance system, adaptable for use in minimally invasive pedicle screw fixation procedures under endoscopic or microscopic visualization, which is easier to implant into the spinal pedicle and will not hinder subsequent procedures performed by the surgeon.
• As discussed above, existing methods and devices used to cure spinal diseases are in need of much improvement. Most conventional spinal fixation devices are too rigid and inflexible. This excessive rigidity causes further abnormalities and diseases of the spine, as well as significant discomfort to the patient. Although some existing spinal fixation devices do provide some level of flexibility, these devices are not designed or manufactured so that varying levels of flexibility may be easily obtained to provide a desired level of flexibility for each particular patient. Additionally, prior art devices having flexible connection units (e.g., rods or plates) pose a greater risk of mechanical failure and do not provide long-term durability and stabilization of the spine. Furthermore, existing methods of performing the spinal fixation procedure are unnecessarily traumatic to the patient due to the difficulty in finding the precise location of the spinal pedicle or sacral of the backbone where the spinal fixation device will be secured.
BRIEF SUMMARY OF THE INVENTION
• The invention addresses the above and other needs by providing an improved method and system for stabilizing an injured or weakened spinal column.
• To overcome the deficiencies of conventional spinal fixation devices, in one embodiment, the inventor of the present invention has invented a novel flexible spinal fixation device with an improved construction and design that is durable and provides a desired level of flexibility and stability. Additionally the inventor of the present invention has invented easily adjustable spinal stabilization devices that can be custom adjusted for individual patients.
• As a result of long-term studies to reduce the operation time required for minimally invasive spinal surgery, to minimize injury to tissues near the surgical area, in another embodiment, the invention provides a method and device for accurately and quickly finding a position of the spinal column in which securing members of the spinal fixation device will be inserted. A novel guidance/marking device is used to indicate the position in the spinal column where the securing members will be inserted.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 illustrates a perspective view of a spinal fixation device in accordance with one embodiment of the invention.
• FIG. 2 illustrates a perspective view of spinal fixation device in accordance with another embodiment of the invention.
• FIG. 3 illustrates an exploded view of thecoupling assembly14 of thepedicle screw2 ofFIGS. 1 and 2, in accordance with one embodiment of the invention.
• FIG. 4 illustrates a perspective view of a flexible rod connection unit in accordance with one embodiment of the invention.
• FIG. 5 illustrates a perspective view of a flexible rod connection unit in accordance with another embodiment of the invention.
• FIG. 6 illustrates a perspective view of a flexible rod connection unit in accordance with a further embodiment of the invention.
• FIG. 7 illustrates a perspective view of a pre-bent flexible rod connection unit in accordance with one embodiment of the invention.
• FIG. 8 illustrates a perspective, cross-sectional view of a flexible portion of connection unit in accordance with one embodiment of the invention.
• FIG. 9 illustrates a perspective, cross-sectional view of a flexible portion of connection unit in accordance with another embodiment of the invention.
• FIG. 10 illustrates a perspective, cross-sectional view of a flexible portion of connection unit in accordance with a further embodiment of the invention.
• FIG. 11 illustrates a perspective view of a flexible rod connection unit in accordance with one embodiment of the invention.
• FIG. 12A illustrates a perspective view of a flexible connection unit having one or more spacers in between two end portions, in accordance with one embodiment of the invention.
• FIG. 12B illustrates an exploded view of the flexible connection unit ofFIG. 12A.
• FIG. 12C provides a view of the male and female interlocking elements of the flexible connection unit ofFIGS. 12A and 12B, in accordance with one embodiment of the invention.
• FIG. 13 shows a perspective view of a flexible connection unit, in accordance with a further embodiment of the invention.
• FIG. 14 illustrates a perspective view of a spinal fixation device in accordance with another embodiment of the invention.
• FIG. 15 illustrates an exploded view of the spinal fixation device ofFIG. 14.
• FIG. 16A shows a perspective view of a flexible plate connection unit in accordance with one embodiment of the invention.
• FIG. 16B illustrates a perspective view of a flexible plate connection unit in accordance with a further embodiment of the invention.
• FIG. 16C shows a side view of the flexible plate connection unit ofFIG. 16A.
• FIG. 16D shows a top view of the flexible plate connection unit ofFIG. 16A.
• FIG. 16E illustrates a side view of the flexible plate connection unit ofFIG. 16A having a pre-bent configuration in accordance with a further embodiment of the invention.
• FIG. 17 is a perspective view of a flexible plate connection unit in accordance with another embodiment of the invention.
• FIG. 18 illustrates a perspective view of a flexible plate connection unit in accordance with another embodiment of the invention.
• FIG. 19 illustrates a perspective view of a hybrid rod-plate connection unit having a flexible middle portion according to a further embodiment of the present invention.
• FIG. 20 is a perspective view of a spinal fixation device that utilizes the hybrid rod-plate connection unit ofFIG. 19.
• FIG. 21 illustrates a perspective view of the spinal fixation device ofFIG. 1 after it has been implanted into a patient's spinal column.
• FIGS. 22A and 22B provide perspective views of spinal fixation devices utilizing the plate connection units ofFIGS. 16A and 16B, respectively.
• FIG. 23A illustrates a perspective view of two pedicle screws inserted into the pedicles of two adjacent vertebrae at a skewed angle, in accordance with one embodiment of the invention.
• FIG. 23B illustrates a structural view of a coupling assembly of a pedicle screw in accordance with one embodiment of the invention.
• FIG. 23C provides a perspective view of a slanted stabilizing spacer in accordance with one embodiment of the invention.
• FIG. 23D illustrates a side view of the slanted stabilizing spacer ofFIG. 23C.
• FIG. 23E is a top view of the cylindrical head of the pedicle screw ofFIG. 23.
• FIG. 24 illustrates a perspective view of a marking and guiding device in accordance with one embodiment of the invention.
• FIG. 25 is an exploded view of the marking and guidance device ofFIG. 24.
• FIG. 26A provides a perspective, cross-section view of a patient's spine after the marking and guiding device ofFIG. 24 has been inserted during surgery.
• FIG. 26B provides a perspective, cross-section view of a patient's spine as an inner trocar of the marking and guiding device ofFIG. 24 is being removed.
• FIGS. 27A and 27B illustrate perspective views of two embodiments of a fiducial pin, respectively.
• FIG. 28 is a perspective view of a pushing trocar in accordance with a further embodiment of the invention.
• FIG. 29A illustrates a perspective, cross-sectional view of a patient's spine as the pushing trocar ofFIG. 28 is used to drive a fiducial pin into a designate location of a spinal pedicle, in accordance with one embodiment of the invention.
• FIG. 29B illustrates a perspective, cross-sectional view of a patient's spine after two fiducial pins have been implanted into two adjacent spinal pedicles, in accordance with one embodiment of the invention.
• FIG. 30 is a perspective view of a cannulated awl in accordance with one embodiment of the invention.
• FIG. 31 is a perspective, cross-sectional view of a patient's spine as the cannulated awl ofFIG. 30 is being used to enlarge an entry hole for a pedicle screw, in accordance with one embodiment of the invention.
• FIG. 32 provides a perspective view of fiducial pin retrieving device, in accordance with one embodiment of the invention.
• FIG. 33 is a perspective view of a pedicle screw having an axial cylindrical cavity for receiving at least a portion of a fiducial pin therein, in accordance with a further embodiment of the invention.
• FIG. 34 is a perspective, cross-sectional view of a patient's spine after one pedicle screw has been implanted into a designated location of a spinal pedicle, in accordance with one embodiment of the invention.
• FIG. 35 is a perspective, cross-sectional view of a patient's spine after two pedicle screws have been implanted into designated locations of two adjacent spinal pedicles, in accordance with one embodiment of the invention.
• FIG. 36A is perspective view of a flexible rod for spinal fixation having a spiral groove cut therein, in accordance with one embodiment of the present invention.
• FIG. 36B provides a cross-sectional view of the flexible rod ofFIG. 36A, taken along lines B-B ofFIG. 36A.
• FIG. 37A illustrates a perspective view of a flexible rod for spinal fixation having transverse tunnels within the body of the rod, in accordance with one embodiment of the invention.
• FIG. 37B is a cross-sectional view of the flexible rod ofFIG. 37A, taken along lines B-B ofFIG. 37A.
• FIG. 38A is a perspective view of a flexible rod for spinal fixation having a spiral groove cut therein and transverse tunnels in the body of the rod, in accordance with a further embodiment of the invention.
• FIG. 38B is a top view of the flexible rod ofFIG. 38A, from the perspective of lines B-B ofFIG. 38A.
• FIG. 39A is a perspective view of a flexible rod for spinal fixation having transverse tunnels within the body of the rod, in accordance with another embodiment of the invention.
• FIG. 39B is a cross-sectional view of the flexible rod ofFIG. 39A, taken along lines B-B of that figure.
• FIG. 39C is an alternative cross-sectional view of the flexible rod ofFIG. 39A, taken along lines B-B of that figure, having substantially orthogonal transverse tunnels in the body of the rod, in accordance with a further embodiment of the invention.
• FIG. 40A illustrates a perspective view of a flexible rod for spinal fixation, in accordance with a further embodiment of the invention.
• FIG. 40B illustrates a cross-sectional view of a flexible rod for spinal fixation in accordance with a further embodiment of the invention.
• FIG. 41A illustrates a cross-section view of a hollow flexible rod for spinal stabilization, with an on-axis tether running through a cavity.
• FIG. 41B illustrates a cross-section view of a hollow flexible rod for spinal stabilization, with an off-axis tether running through a cavity.
• FIG. 41C illustrates a cross-section view of a hollow flexible rod for spinal stabilization, with a pre-tensioned off-axis tether running through a cavity.
• FIG. 42A illustrates displacement of a free end of a longitudinal body in response to an externally applied force.
• FIG. 42B is a graph of displacement versus applied force for the system shown inFIG. 42A.
• FIG. 43 illustrates a cross-sectional view of a longitudinal member with an internal tether, the tension or compression of which is adjustable according to one embodiment of the invention.
• FIG. 44 illustrates a cross-sectional view of a longitudinal member with an internal tether, the tension or compression of which is adjustable, according to another embodiment of the invention.
• FIG. 45 illustrates a cross-sectional view of a longitudinal member with an internal tether, the tension or compression of which is adjustable according to yet another embodiment of the invention.
• FIG. 46 illustrates a perspective view of a longitudinal member similar to that shown inFIG. 45.
• FIG. 47 illustrates a longitudinal member having at least one external tether coupled to respective ends of the longitudinal member, in accordance with a further embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• The invention is described in detail below with reference to the figures wherein like elements are referenced with like numerals throughout.
• FIG. 1 depicts a spinal fixation device in accordance with one embodiment of the present invention. The spinal fixation device includes two securing members2 (designated as2′ and2″), and aflexible fixation rod4 configured to be received and secured within acoupling assembly14, as described in further detail below with respect toFIG. 3. Each securingmember2 includes a threaded screw-type shaft10 configured to be inserted and screwed into a patient's spinal pedicle. As shown inFIG. 1, the screw-type shaft10 includes an externalspiral screw thread12 formed over the length of theshaft10 and a conical tip at the end of theshaft10 configured to be inserted into the patient's spinal column at a designated location. Other known forms of the securingmember2 may be used in connection with the present invention provided the securingmember2 can be inserted and fixed into the spinal column and securely coupled to therod4.
• As described above, the spinal fixation device is used for surgical treatment of spinal diseases by mounting securingmembers2 at desired positions in the spinal column. In one embodiment, therod4 extends across two or more vertebrae of the spinal column and is secured by the securingmembers2 so as to stabilize movement of the two or more vertebrae.
• FIG. 2 illustrates a perspective view of a spinal fixation device in accordance with a further embodiment of the present invention. The spinal fixation device ofFIG. 2 is similar to the spinal fixation device ofFIG. 1 except that therod4 comprises a flexiblemiddle portion8 juxtaposed between tworigid end portions9 of therod4.
• FIG. 3 provides an exploded view of the securingmember2 ofFIGS. 1 and 2 illustrating various components of thecoupling assembly14, in accordance with one embodiment of the invention. As shown inFIG. 3, thecoupling assembly14 includes: acylindrical head16 located at a top end of the screw-type shaft10, a spiral thread or groove18 formed along portions of the inner wall surface of thecylindrical head16, and aU-shaped seating groove20 configured to receive therod4 therein. Thecoupling assembly14 further comprises an outside-threadednut22 having aspiral thread24 formed on the outside lateral surface of thenut22, wherein thespiral thread24 is configured to mate with theinternal spiral thread18 of thecylindrical head16. In a further embodiment, thecoupling assembly14 includes a fixingcap26 configured to be mounted over a portion of thecylindrical head16 to cover and protect the outside-threadednut22 and more securely holdrod4 withinseating groove20. In one embodiment an inner diameter of the fixinggap26 is configured to securely mate with the outer diameter of thecylindrical head16. Other methods of securing the fixingcap26 to the cylindrical head, such as correspondingly located notches and groove (not shown), would be readily apparent to those of skill in the art. In preferred embodiments the components and parts of the securingmember2 may be made of highly rigid and durable bio-compatible materials such as: stainless steel, iron steel, titanium or titanium alloy. Such materials are known in the art. As also known in the art, and used herein, “bio-compatible” materials refers to those materials that will not cause any adverse chemical or immunological reactions after being implanted into a patient's body.
• As shown inFIGS. 1 and 2, in preferred embodiments, therod4 is coupled to the securing means2 by seating therod4 horizontally into theseating groove20 of the coupling means14 perpendicularly to the direction of the length of the threadedshaft10 of securingmember2. The outside threadednut22 is then received and screwed into thecylindrical head16 above therod4 so as to secure therod4 in theseating groove20. The fixingcap26 is then placed over thecylindrical head16 to cover, protect and more firmly secure the components in the internal cavity of thecylindrical head16.FIGS. 4-7 illustrate perspective views of various embodiments of arod4 that may be used in a fixation device, in accordance with the present invention.FIG. 4 illustrates therod4 ofFIG. 1 wherein the entire rod is made and designed to be flexible. In this embodiment,rod4 comprises a metal tube or pipe having acylindrical wall5 of a predefined thickness. In one embodiment, in order to provide flexibility to therod4, thecylindrical wall5 is cut in a spiral fashion along the length of therod4 to form spiral cuts orgrooves6. As would be apparent to one of ordinary skill in the art, the width and density of thespiral grooves6 may be adjusted to provide a desired level of flexibility. In one embodiment, thegrooves6 are formed from very thin spiral cuts or incisions that penetrate through the entire thickness of the cylindrical wall of therod4. As known to those skilled in the art, the thickness and material of thetubular walls5 also affect the level of flexibility.
• In one embodiment, therod4 is designed to have a flexibility that substantially equals that of a normal back. Flexibility ranges for a normal back are known by those skilled in the art, and one of ordinary skill can easily determine a thickness and material of thetubular walls5 and a width and density of thegrooves6 to achieve a desired flexibility or flexibility range within the range for a normal back. When referring to thegrooves6 herein, the term “density” refers to tightness of thespiral grooves6 or, in other words, the distance betweenadjacent groove lines6 as shown inFIG. 4, for example. However, it is understood that the present invention is not limited to a particular, predefined flexibility range. In one embodiment, in addition to having desired lateral flexibility characteristics, the rigidity of therod4 should be able to endure a vertical axial load applied to the patient's spinal column along a vertical axis of the spine in a uniform manner with respect to the rest of the patient's natural spine.
• FIG. 5 illustrates therod4 ofFIG. 2 wherein only amiddle portion8 is made and designed to be flexible and twoend portions9 are made to be rigid. In one embodiment, metal end rings orcaps9′, having no grooves therein, may be placed over respective ends of therod4 ofFIG. 4 so as make theend portions9 rigid. The rings orcaps9′ may be permanently affixed to the ends of therod4 using known methods such as pressing and/or welding the metals together. In another embodiment, thespiral groove6 is only cut along the length of themiddle portion8 and theend portions9 comprise thetubular wall5 withoutgrooves6. Without thegrooves6, thetubular wall5, which is made of a rigid metal or metal hybrid material, exhibits high rigidity.
• FIG. 6 illustrates a further embodiment of therod4 having multiple sections, twoflexible sections8 interleaved between threerigid sections9. This embodiment may be used, for example, to stabilize three adjacent vertebrae with respect to each other, wherein three pedicle screws are fixed to a respective one of the vertebrae and the threerigid sections9 are connected to acoupling assembly14 of arespective pedicle screw2, as described above with respect toFIG. 3. Each of theflexible sections8 andrigid sections9 may be made as described above with respect toFIG. 5.
• FIG. 7 illustrates another embodiment of therod4 having a pre-bent structure and configuration to conform to and maintain a patient's curvature of the spine, known as “lordosis,” while stabilizing the spinal column. Generally, a patient's lumbar is in the shape of a ‘C’ form, and the structure of therod4 is formed to coincide to the normal lumbar shape when utilized in the spinal fixation device ofFIG. 2, in accordance with one embodiment of the invention. In one embodiment, thepre-bent rod4 includes amiddle portion8 that is made and designed to be flexible interposed between tworigid end portions9. Themiddle portion8 andend portions9 may be made as described above with respect toFIG. 5. Methods of manufacturing metallic or metallic-hybrid tubular rods of various sizes, lengths and pre-bent configurations are well-known in the art. Additionally, or alternatively, the pre-bent structure and design of therod4 may offset a skew angle when two adjacent pedicle screws are not inserted parallel to one another, as described in further detail below with respect toFIG. 23A.
• Additional designs and materials used to create a flexibletubular rod4 or flexiblemiddle portion8 are described below with respect toFIGS. 8-10.FIG. 8 illustrates a perspective, cross-sectional view of a flexibletubular rod4, orrod portion8 in accordance with one embodiment of the invention. In this embodiment, theflexible rod4,8 is made from afirst metal tube5 having aspiral groove6 cut therein as described above with respect toFIGS. 4-7. Asecond tube30 havingspiral grooves31 cut therein and having a smaller diameter than thefirst tube5 is inserted into the cylindrical cavity of thefirst tube5. In one embodiment, thesecond tube30 hasspiral grooves31 which are cut in an opposite spiral direction with respect to thespiral grooves6 cut in thefirst tube5, such that the rotational torsion characteristics of thesecond tube30 offset at least some of the rotational torsion characteristics of thefirst tube5. The secondflexible tube30 is inserted into the core of the first tube to provide further durability and strength to theflexible rod4,8. Thesecond tube30 may be made of the same or different material than thefirst tube5. In preferred embodiments, the material used to manufacture the first andsecond tubes5 and30, respectively, may be any one or combination of the following exemplary metals: stainless steel, iron steel, titanium, and titanium alloy.
• FIG. 9 illustrates a perspective, cross-sectional view of aflexible rod4,8 in accordance with a further embodiment of the invention. In this embodiment, theflexible rod4,8 includes an inner core made of ametallic wire32 comprising a plurality of overlapping thin metallic yarns, such as steel yarns, titanium yarns, or titanium-alloy yarns. Thewire32 is encased by a metal, or metal hybrid,flexible tube5 havingspiral grooves6 cut therein, as discussed above. The number and thickness of the metallic yarns in thewire32 also affects the rigidity and flexibility of therod4,8. By changing the number, thickness or material of the yarns flexibility can be increased or decreased. Thus, the number, thickness and/or material of the metallic yarns in thewire32 can be adjusted to provide a desired rigidity and flexibility in accordance with a patient's particular needs. Those of ordinary skill in the art can easily determine the number, thickness and material of the yarns, in conjunction with a given flexibility of thetube5 in order to achieve a desired rigidity v. flexibility profile for therod4,8.
• FIG. 10 shows yet another embodiment of aflexible rod4 wherein theflexible tube5 encases a non-metallic,flexible core34. The core34 may be made from known biocompatible shape memory alloys (e.g., NITINOL), or biocompatible synthetic materials such as: carbon fiber, Poly Ether Ether Ketone (PEEK), Poly Ether Ketone Ketone Ether Ketone (PEKKEK), or Ultra High Molecular Weight Poly Ethylene (UHMWPE).
• FIG. 11 illustrates a perspective view of another embodiment of theflexible rod35 in which a plurality ofmetal wires32, as described above with respect toFIG. 9, are interweaved or braided together to form a braidedmetal wire rod35. Thus, the braidedmetal wire rod35 can be made from the same materials as themetal wire32. In addition to the variability of the rigidity and flexibility of thewire32 as explained above, the rigidity and flexibility of thebraided rod35 can be further modified to achieve desired characteristics by varying the number and thickness of thewires32 used in thebraided structure35. For example, in order to achieve various flexion levels or ranges within the known flexion range of a normal healthy spine, those of ordinary skill in the art can easily manufacture various designs of thebraided wire rod35 by varying and measuring the flexion provided by different gauges, numbers and materials of the wire used to create thebraided wire rod35. In a further embodiment each end of the braidedmetal wire rod35 is encased by a rigid metal cap orring9′ as described above with respect toFIGS. 5-7, to provide arod4 having a flexiblemiddle portion8 andrigid end portions9. In a further embodiment (not shown), the metalbraided wire rod35 may be utilized as a flexible inner core encased by ametal tube5 havingspiral grooves6 cut therein to create aflexible metal rod4 orrod portion8, in a similar fashion to the embodiments shown inFIGS. 8-10. As used herein the term “braid” or “braided structure” encompasses two or more wires, strips, strands, ribbons and/or other shapes of material interwoven in an overlapping fashion. Various methods of interweaving wires, strips, strands, ribbons and/or other shapes of material are known in the art. Such interweaving techniques are encompassed by the present invention. In another exemplary embodiment (not shown), theflexible metal rod35 includes a braided metal structure having two or more metal strips, strands or ribbons interweaved in a diagonally overlapping pattern.
• FIG. 12A illustrates a further embodiment of aflexible connection unit36 having tworigid end portions9′ and an exemplary number ofrigid spacers37. In one embodiment, therigid end portions9′ and spacers can be made of bio-compatible metal or metal-hybrid materials as discussed above. Theconnection unit36 further includes aflexible wire32, as discussed above with respect to FIG.9′, which traverses an axial cavity or hole (not shown) in each of therigid end portions9′ andspacers37.FIG. 12B illustrates an exploded view of theconnection unit36 that further shows how thewire32 is inserted through center axis holes of therigid end portions9′ andspacers37. As further shown inFIG. 12B, each of theend portions9′ andspacers37 include a male interlockingmember38 which is configured to mate with a female interlocking cavity (not shown) in the immediatelyadjacent end portion9′ orspacer37.FIG. 12 C illustrates an exploded side view and indicates with dashed lines the location and configuration of the female interlockingcavity39 for receiving corresponding male interlockingmembers38.
• FIG. 13 shows a perspective view of a flexible connection unit40 in accordance with another embodiment of the invention. The connection40 is similar to theconnection unit36 described above, however, the spacers42 are configured to have the same shape and design as therigid end portions9′. Additionally, theend portions9′ have an exit hole or groove44 located on a lateral side surface through which thewire32 may exit, be pulled taut, and clamped or secured using a metal clip (not shown) or other known techniques. In this way, the length of theflexible connection unit36 or40 may be varied at the time of surgery to fit each patient's unique anatomical characteristics. In one embodiment, thewire32 may be secured using a metallic clip or stopper (not shown). For example, a clip or stopper may include a small tubular cylinder having an inner diameter that is slightly larger than the diameter of thewire32 to allow thewire32 to pass therethrough. After thewire32 is pulled to a desired tension through the tubular stopper, the stopper is compressed so as to pinch thewire32 contained therein. Alternatively, thewire32 may be pre-secured using known techniques during the manufacture of theconnection units36,40 having a predetermined number ofspacers37,42 therein.
• FIG. 14 depicts a spinal fixation device according to another embodiment of the present invention. The spinal fixation device includes: at least two securingmembers2 containing an elongatescrew type shaft10 having anexternal spiral thread12, and acoupling assembly14. The device further includes aplate connection unit50, or simply “plate50,” configured to be securely connected to thecoupling parts14 of the two securingmembers2. Theplate50 comprises tworigid connection members51 each having a planar surface and joined to each other by a flexiblemiddle portion8. The flexiblemiddle portion8 may be made in accordance with any of the embodiments described above with respect toFIGS. 4-11. Eachconnection member51 contains acoupling hole52 configured to receive therethrough a second threaded shaft54 (FIG. 15) of thecoupling assembly14.
• As shown inFIG. 15, thecoupling assembly14 of the securingmember2 includes abolt head56 adjoining the top of the first threadedshaft10 and having a circumference or diameter greater than the circumference of the first threadedshaft10. The second threadedshaft54 extends upwardly from thebolt head56. Thecoupling assembly14 further includes anut58 having an internal screw thread configured to mate with the second threadedshaft54, and one ormore washers60, for clamping theconnection member51 against the top surface of thebolt head56, thereby securely attaching theplate50 to thepedicle screw2.
• FIGS. 16A and 16B illustrate two embodiments of a plate connection unit40 having at least twocoupling members51 and at least oneflexible portion8 interposed between and attached to twoadjacent connection members51. As shown inFIGS. 16A and 16B, the flexiblemiddle portion8 comprises a flexible metalbraided wire structure36 as described above with respect toFIG. 11. However, theflexible portion8 can be designed and manufactured in accordance with any of the embodiments described above with respect toFIGS. 4-11, or combinations thereof.FIGS. 16C and 16D illustrate a side view and top view, respectively, of theplate50 ofFIG. 16A. The manufacture of different embodiments of theflexible connection units50 and58 having different types of flexiblemiddle portions8, as described above, is easily accomplished using known metallurgical, organic polymer, natural resin, or composite materials, and compatible manufacturing and machining processes.
• FIG. 16E illustrate a side view of a pre-bentplate connection unit50′, in accordance with a further embodiment of the invention. Thisplate connection unit50′ is similar to theplate50 except thatconnection members51′ are formed or bent at an angle θ from aparallel plane53 during manufacture of theplate connection unit50′. As discussed above with respect to the pre-bent rod-like connection unit4 ofFIG. 7, this pre-bent configuration is designed to emulate and support a natural curvature of the spine (e.g., lordosis). Additionally, or alternatively, this pre-bent structure may offset a skew angle when two adjacent pedicle screws are not inserted parallel to one another, as described in further detail below with respect toFIG. 23A.
• FIG. 17 illustrates a perspective view of aplate connection unit60 having twoplanar connection members62 each having acoupling hole64 therein for receiving the second threaded shaft44 of thepedicle screw2. A flexiblemiddle portion8 is interposed between the twoconnection members62 and attached thereto. In one embodiment, the flexiblemiddle portion8 is made in a similar fashion to wire32 described above with respect toFIG. 9, except it has a rectangular configuration instead of a cylindrical or circular configuration as shown inFIG. 9. It is understood, however, that the flexiblemiddle portion8 may be made in accordance with the design and materials of any of the embodiments previously discussed.
• FIG. 18 illustrates a perspective view of a further embodiment of theplate60 ofFIG. 17 wherein thecoupling hole64 includes one or morenut guide grooves66 cut into the top portion of theconnection member62 to seat and fix the nut58 (FIG. 15) into thecoupling hole64. Thenut guide groove66 is configured to receive and hold at least a portion of thenut58 therein and prevent lateral sliding of thenut58 within thecoupling hole64 after theconnection member62 has been clamped to thebolt head56 of thepedicle screw2.
• FIG. 19 illustrates a perspective view of a hybrid plate androd connection unit70 having a rigid rod-like connection member4,9 or9′, as described above with respect toFIGS. 4-7, at one end of theconnection unit70 and a plate-like connection member51 or62, as described above with respect toFIGS. 14-18, at the other end of theconnection unit70. In one embodiment, interposed between rod-like connection member9 (9′) and the plate-like connection member52 (64) is aflexible member8. Theflexible member8 may be designed and manufactured in accordance with any of the embodiments discussed above with reference toFIGS. 8-13.
• FIG. 20 illustrates a perspective view of a spinal fixation device that utilizes the hybrid plate androd connection unit70 ofFIG. 19. As shown inFIG. 20, this fixation device utilizes two types of securing members2 (e.g., pedicle screws), the first securingmember2′ being configured to securely hold the plate connection member42(64) as described above with respect toFIG. 15, and the second securingmember2″ being configured to securely hold therod connection member4,9 or9′, as described above with respect toFIG. 3.
• FIG. 21 illustrates a perspective top view of two spinal fixation devices, in accordance with the embodiment illustrated inFIG. 1, after they are attached to twoadjacent vertebrae80 and82 to flexibly stabilize the vertebrae.FIGS. 22A and 22B illustrate perspective top views of spinal fixation devices using the flexible stabilizingmembers50 and58 ofFIGS. 16A and 16B, respectively, after they are attached to two or more adjacent vertebrae of the spine.
• FIG. 23A illustrates a side view of a spinal fixation device after it has been implanted into the pedicles of two adjacent vertebrae. As shown in this figure, the pedicle screws2 are mounted into the pedicle bone such that acenter axis80 of thescrews2 are offset by an angle θ from aparallel plane82 and the center axes80 of the twoscrews2 are offset by an angle of approximately 2θ from each other. This type of non-parallel insertion of the pedicle screws2 often results due to the limited amount of space that is available when performing minimally invasive surgery. Additionally, the pedicle screws2 may have a tendency to be skewed from parallel due to a patient's natural curvature of the spine (e.g., lordosis). Thus, due to the non-parallel nature of how the pedicle screws2 are ultimately fixed to the spinal pedicle, it is desirable to offset this skew when attaching a rod or plate connection unit to each of the pedicle screws2.
• FIG. 23B illustrates a side view of the head of the pedicle screw in accordance with one embodiment of the invention. Thescrew2 includes acylindrical head84 which is similar to thecylindrical head16 described above with respect toFIG. 3 except that thecylindrical head84 includes a slantedseat86 configured to receive and hold aflexible rod4 in a slanted orientation that offsets the slant or skew θ of thepedicle screw2 as described above. Theimproved pedicle screw2 further includes a slanted stabilizingspacer88 which is configured to securely fit inside the cavity of thecylindrical head84 and hold down therod4 at the same slant as theslanted seat86. Thepedicle screw2 further includes an outside threadednut22 configured to mate with spiral threads along the interior surface (not shown) of thecylindrical head84 for clamping down and securing the slantedspacer88 and therod4 to the slantedseat86 and, hence, to thecylindrical head84 of thepedicle screw2.
• FIG. 23C shows a perspective view of the slantedspacer88, in accordance with embodiment of the invention. Thespacer88 includes a circularmiddle portion90 and two rectangular-shapedend portions92 extending outwardly from opposite sides of the circularmiddle portion90.FIG. 23D shows a side view of thespacer88 that further illustrates the slant from one end to another to compensate or offset the skew angle θ of thepedicle screw2.FIG. 23E illustrates a top view of thecylindrical head84 configured to receive arod4 and slantedspacer88 therein. Therod4 is received through two openings orslots94 in the cylindrical walls of thecylindrical head84, which allow therod4 to enter the circular orcylindrical cavity96 of thecylindrical head84 and rest on top of the slantedseat86 formed within the circular orcylindrical cavity94. After therod4 is positioned on the slantedseat86, the slanted stabilizingspacer88 is received in thecavity96 such that the two rectangular-shapedend portions92 are received within the twoslots94, thereby preventing lateral rotation of thespacer88 within thecylindrical cavity96. Finally, the outside threadednut22 and fixingcap26 are inserted on top of the slantedspacer88 to securely hold thespacer88 androd4 within thecylindrical head84.
• FIG. 24 illustrates a perspective view of a marking andguidance device100 for marking a desired location on the spinal pedicle where apedicle screw2 will be inserted and guiding thepedicle screw2 to the marked location using a minimally invasive surgical technique. As shown inFIG. 24, the markingdevice100 includes a tubularhollow guider52 which receives within its hollow aninner trocar104 having asharp tip105 at one end that penetrates a patient's muscle and tissue to reach the spinal pedicle. theinner trocar104 further includes atrocar grip106 at the other end for easy insertion and removal of thetrocar104. In one embodiment, the marking andguidance device100 includes aguider handle108 to allow for easier handling of thedevice100.
• As shown inFIG. 25, thetrocar104 is in the form of a long tube or cylinder having a diameter smaller than the inner diameter of the hollow of theguider102 so as to be inserted into the hollow of thetubular guider102. Thetrocar104 further includes a sharp orpointed tip105 for penetrating the vertebral body through the pedicle. Thetrocar104 further includes atrocar grip106 having a diameter larger than the diameter of the hollow of theguider tube102 in order to stop thetrocar104 from sliding completely through the hollow. Thetrocar grip106 also allows for easier handling of thetrocar104.
• FIGS. 26A and 26B provide perspective views of the marking andguidance device100 after it has been inserted into a patient's back and pushed through the muscle and soft tissue to reach a desired location on the spinal pedicle. The desired location is determined using known techniques such as x-ray or radiographic imaging for a relatively short duration of time. After the marking andguidance device100 has been inserted, prolonged exposure of the patient to x-ray radiation is unnecessary. As shown inFIG. 26B, after theguidance tube102 is positioned over the desired location on the pedicle, theinner trocar104 is removed to allow fiducial pins (not shown) to be inserted into the hollow of theguidance tube102 and thereafter be fixed into the pedicle.
• FIGS. 27A and 27B illustrate perspective views of two embodiments of thefiducial pins110 and112, respectively. As mentioned above, thefiducial pins110 and112 according to the present invention are inserted and fixed into the spinal pedicle after passing through thehollow guider102. Thepins110 and112 have a cylindrical shape with a diameter smaller than the inner diameter of the hollow of theguider tube102 in order to pass through the hollow of theguider102. An end of each fiducial pin is asharp point111 configured to be easily inserted and fixed into the spinal pedicle of the spinal column. In one embodiment, as shown inFIG. 27B, the other end of the fiducial pin incorporates a threadedshaft114 which is configured to mate with an internally threaded tube of a retriever (not shown) for extraction of thepin112. This retriever is described in further detail below with respect toFIG. 32.
• Thefiducial pins110,112 are preferably made of a durable and rigid biocompatible metal (e.g., stainless steel, iron steel, titanium, titanium alloy) for easy insertion into the pedicle bone. In contrast to prior art guide wires, because of its comparatively shorter length and more rigid construction, thefiducial pins110,112 are easily driven into the spinal pedicle without risk of bending or structural failure. As explained above, the process of driving in prior art guidance wires was often very difficult and time-consuming. The insertion of thefiducial pins110,112 into the entry point on the spinal pedicle is much easier and convenient for the surgeon and, furthermore, does not hinder subsequent procedures due to a guide wire protruding out of the patient's back.
• FIG. 28 shows a cylindrical pushingtrocar116 having acylindrical head118 of larger diameter than the body of the pushingtrocar116. The pushingtrocar116, according to the present invention, is inserted into the hollow of theguider102 after thefiducial pin110 or112 has been inserted into the hollow of theguider102 to drive and fix thefiducial pin110 or112 into the spinal pedicle. During this pin insertion procedure, a doctor strikes thetrocar head118 with a chisel or a hammer to drive thefiducial pin110 and112 into the spinal pedicle. In preferred embodiments, the pushingtrocar116 is in the form of a cylindrical tube, which has a diameter smaller than the inner diameter of the hollow of theguider tube112. The pushingtrocar116 also includes acylindrical head118 having a diameter larger than the diameter of the pushingtrocar116 to allow the doctor to strike it with a chisel or hammer with greater ease. Of course, in alternative embodiments, a hammer or chisel is not necessarily required. For example, depending on the circumstances of each case, a surgeon may choose to push or tap thehead118 of the pushingtrocar116 with the palm of his or her hand or other object.
• FIG. 29A illustrates how a hammer ormallet120 and the pushingtrocar116 may be used to drive thepin110,112 through the hollow of theguider tube102 and into the designated location of the spinal pedicle.FIG. 29B illustrates a perspective cross-sectional view of the spinal column after twofiducial pins110,112 have been driven and fixed into two adjacent vertebrae.
• After thefiducial pins110 or112 have been inserted into the spinal pedicle as discussed above, in one embodiment, a larger hole or area centered around eachpin110,112 is created to allow easer insertion and mounting of apedicle screw2 into the pedicle bone. The larger hole is created using a cannulatedawl122 as shown inFIG. 30. The cannulatedawl122 is inserted over thefiducial pin110,112 fixed at the desired position of the spinal pedicle. Theawl122 is in the form of a cylindrical hollow tube wherein an internal diameter of the hollow is larger than the outer diameter of thefiducial pins110 and112 so that thepins110,112 may be inserted into the hollow of theawl122. Theawl122 further includes one or moresharp teeth124 at a first end for cutting and grinding tissue and bone so as to create the larger entry point centered around thefiducial pin110,112 so that thepedicle screw2 may be more easily implanted into the spinal pedicle.FIG. 31 illustrates a perspective cross-sectional view of a patient's spinal column when the cannulatedawl122 is inserted into a minimally invasive incision in the patient's back, over afiducial pin110,112 to create a larger insertion hole for a pedicle screw2 (not shown). As shown inFIG. 31, aretractor130 has been inserted into the minimally invasive incision over the surgical area and a lower tubular body of theretractor130 is expanded to outwardly push surrounding tissue away from the surgical area and provide more space and a visual field for the surgeon to operate. In order to insert theretractor130, in one embodiment, the minimally invasive incision is made in the patient's back between and connecting the two entry points of theguide tube102 used to insert the twofiducial pins110,112. Before theretractor130 is inserted, prior expansion of the minimally invasive incision is typically required using a series of step dilators (not shown), each subsequent dilator having a larger diameter than the previous dilator. After the last step dilator is in place, theretractor130 is inserted with its lower tubular body in a retracted, non-expanded state. After theretractor130 is pushed toward the spinal pedicle to a desired depth, the lower tubular portion is then expanded as shown inFIG. 31. The use of step dilators and retractors are well known in the art.
• After the cannulatedawl122 has created a larger insertion hole for thepedicle screw2, in one embodiment, thefiducial pin110,112 is removed. As discussed above, if thefiducial pin112 has been used, a retrievingdevice140 may be used to remove thefiducial pin112 before implantation of apedicle screw2. As shown inFIG. 32, theretriever140 comprises a long tubular or cylindrical portion having an internally threadedend142 configured to mate with the externally threadedtop portion114 of thefiducial pin112. After theretriever end142 has been screwed onto the threadedend114, a doctor my pull thefiducial pin112 out of the spinal pedicle. In another embodiment, if thefiducial pin110 without a threaded top portion has been used, appropriate tools (e.g., specially designed needle nose pliers) may be used to pull thepin110 out.
• In alternate embodiments, thefiducial pins110,112 are not extracted from the spinal pedicle. Instead, a specially designedpedicle screw144 may be inserted into the spinal pedicle over thepin110,112 without prior removal of thepin110,112. As shown inFIG. 33, the specially designedpedicle screw144 includes an externally threadedshaft10 and a coupling assembly14 (FIG. 3) that includes a cylindrical head16 (FIG. 3) for receiving a flexible rod-shaped connection unit4 (FIGS. 4-13). Alternatively, thecoupling assembly14 may be configured to receive a plate-like connection unit as shown inFIGS. 14-20. Thepedicle screw144 further includes a longitudinal axial channel (not shown) inside the threadedshaft10 having anopening146 at the tip of theshaft10 and configured to receive thefiducial pin110,112 therein.
• FIG. 34 illustrates a perspective cross-sectional view of the patient's spinal column after apedicle screw2 has been inserted into a first pedicle of the spine using aninsertion device150. Various types ofinsertion devices150 known in the art may be used to insert thepedicle screw2. As shown inFIG. 34, after afirst pedicle screw2 has been implanted, theretractor130 is adjusted and moved slightly to provide space and a visual field for insertion of a second pedicle screw at the location of the secondfiducial pin110,112.
• FIG. 35 provides a perspective, cross sectional view of the patient's spinal column after twopedicle screws2 have been implanted in two respective adjacent pedicles of the spine, in accordance with the present invention. After the pedicle screws2 are in place, a flexible rod, plate or hybrid connection unit as described above with respect toFIGS. 4-20 may be connected to the pedicle screws to provide flexible stabilization of the spine. Thereafter, theretractor130 is removed and the minimally invasive incision is closed and/or stitched.
• FIG. 36A illustrates a perspective view of aflexible rod200 for spinal fixation, in accordance with a further embodiment of the invention. Therod200 is configured to be secured by securingmembers2 as described above with reference toFIGS. 1-3. In preferred embodiments, therod200, androds210,220,230 and240 described below, are comprised of a solid, cylindrically-shaped rod made of known bio-compatible materials such as: stainless steel, iron steel, titanium, titanium alloy, NITINOL, and other suitable metal compositions or materials. As shown inFIG. 36A,spiral grooves202 are cut or formed along at least a portion of the length of the cylindrical body of therod200. In an exemplary embodiment, the length of the rod “l” may be between 4 and 8 centimeters (cm), and its cylindrical diameter “D” is between 4-8 millimeters (mm). Thespiral grooves202 have a width “w” between 0.1 and 0.5 mm and a spiral angle θ between 50 and 85 degrees from horizontal. The distance betweenspiral grooves202 can be between 3 and 6 mm. However, as understood by those skilled in the art, the above dimensions are exemplary only and may be varied to achieve desired flexibility, torsion and strength characteristics that are suitable for a particular patient or application.
• FIG. 36B illustrates a cross-sectional view of theflexible rod200, taken along lines B-B ofFIG. 36A. As shown,spiral groove202 is cut toward the center longitudinal axis of thecylindrical rod200. The groove may be formed continuously in a spiral fashion, as a helix or an interrupted helix for a solid or hollow rod, or are as disconnected circumferential grooves for a solid rod. If hollow rods have disconnected circumferential grooves formed in them, the grooves can only partially penetrate the rod material to avoid discontinuities. In one embodiment, the depth of thegroove202 is approximately equal to the cylindrical radius of therod200, as shown inFIG. 36B, and penetrates as deep as the center longitudinal axis of thecylindrical rod200. However, the cross sectional area and shape of the rod, groove depth, groove width, groove cross-section shape, and groove to groove spacing of the grooved portion of the longitudinal member can be varied to adjust mechanical and structural characteristics as desired. For example, deepening or widening grooves increases flexibility, while increasing groove-to-groove spacing decreases flexibility. This can be used to modify extent of rod bending at a fixed bending force, custom tailor the bent shape of the rod, and equalize mechanical stresses in the rod during bending in order to minimize material fatigue and improve rod reliability.
• FIG. 37A illustrates aflexible rod210 for spinal fixation in accordance with another embodiment of the invention. Therod210 includes a plurality of transverse holes ortunnels212 drilled or formed within the body of therod210. In one embodiment, thetunnels212 pass through a center longitudinal axis of thecylindrical rod210 at an angle Φ from horizontal. The openings for eachrespective tunnel212 are located on opposite sides of the cylindrical wall of therod210 andadjacent tunnels212 share a common opening on one side of the cylindrical wall, forming a zigzag pattern ofinterior tunnels212 passing transversely through the central longitudinal axis of therod210, as shown inFIG. 37A. In one embodiment, the diameter D of eachtunnel212 may be varied between 0.2 to 3 mm, depending the desired mechanical and structural characteristics (e.g., flexibility, torsion and strength) of therod210. However, it is understood that these dimensions are exemplary and other diameters D may be desired depending on the materials used and the desired structural and mechanical characteristics. Similarly, the angle from horizontal Φ may be varied to change the number oftunnels212 or the distance betweenadjacent tunnels212.
• FIG. 37B illustrates a cross-sectional view of theflexible rod210 taken along lines B-B ofFIG. 37A. Thetunnel212 cuts through the center cylindrical axis of therod210 such that openings of thetunnel212 are formed at opposite sides of the cylindrical wall of therod210.
• FIG. 38A illustrates a perspective view of aflexible rod220 for spinal fixation, in accordance with a further embodiment of the invention.Rod220 incorporates thespiral grooves202 described above with reference toFIGS. 36A and 36B as well as thetransverse tunnels212 described above with respect toFIGS. 37A and 37B. Thespiral grooves202 are cut into the surface of the cylindrical wall of therod220 toward a center longitudinal axis of therod220. As discussed above, the dimensions of thespiral grooves202 and their angle from horizontal θ (FIG. 36A) may be varied in accordance with desired mechanical and structural characteristics. Similarly, the dimensions of thetransverse tunnels212 and their angle from horizontal Φ (FIG. 37A) may be varied in accordance with desired mechanical and structural characteristics. In one embodiment, the angles θ and Φ are substantially similar such that the openings of thetunnels212 substantially coincide with thespiral grooves202 on opposite sides of the cylindrical wall of therod220.
• FIG. 38B shows a top view of theflexible rod220 taken along the perspective indicated by lines B-B ofFIG. 38A. As shown inFIG. 38B, the openings of thetunnels212 coincide with thespiral grooves202. By providing bothspiral grooves202 andtransverse tunnels212 within asolid rod220, many desired mechanical and structural characteristics that are suitable for different patients, applications and levels of spinal fixation may be achieved.
• FIG. 39A illustrates aflexible rod230 for spinal fixation, in accordance with another embodiment of the invention. Therod230 includes a plurality oftransverse tunnels232 formed in the body of therod230. Thetunnels232 are substantially similar to thetunnels212 described above with respect toFIGS. 37A and 37B, however, thetunnels232 are not linked together in a zigzag pattern. Rather, eachtunnel232 is substantially parallel to its immediateadjacent tunnels232 and the openings of onetunnel232 do not coincide with the openings ofadjacent tunnels232. As shown inFIG. 39A, the angle from horizontal Φ in this embodiment is approximately 90 degrees. However, it is understood that other angles Φ may be incorporated in accordance with the present invention. It is further understood that the dimensions, size and shape of the tunnels232 (as well as tunnels212) may be varied to achieve desired mechanical and structural characteristics. For example, the cross-sectional shape of thetunnels212 and232 need not be circular. Instead, for example, they may be an oval or diamond shape, or other desired shape.
• FIG. 39B illustrates a cross-sectional view of therod230 taken along lines B-B ofFIG. 39A. As shown inFIG. 39B, thetransverse tunnel232 travels vertically and transversely through the center longitudinal axis of therod230.FIG. 39C illustrates a cross-sectional view of a further embodiment of therod230, wherein an additionaltransverse tunnel232′ is formed substantially orthogonal to the firsttransverse tunnel232 and intersects the firsttransverse tunnel232 at the center, cylindrical axis point. In this way, further flexibility of therod230 may be provided as desired.
• FIG. 40A illustrates a perspective view of aflexible rod240, in accordance with a further embodiment of the invention. Therod240 includes a plurality of interleavedtransverse tunnels232 and242 which are substantially orthogonal to each other and which do not intersect, as shown inFIG. 40A. In another embodiment, a cross-sectional view of which is shown inFIG. 40B,adjacent tunnels232 and242 need not be orthogonal to one another. Eachtunnel232,242 can be offset at a desired angle ω from its immediately precedingadjacent tunnel232,242. As can be verified by those of skill in the art, without undue experimentation, by varying the dimensions of the tunnels, their numbers, and their angular directions with respect to one another, various desired mechanical and structural characteristics for flexible rods used in spinal fixation devices may be achieved.
• FIG. 41A illustrates a cross-sectional view of an embodiment of the invention with a longitudinal member for a spinal stabilization system having aflexible section284 betweenends280 and282 that are configured to mate with securingmember2 ofFIG. 3.FIG. 41A further illustrates that theflexible section284 is hollow, having acavity287 through which runs atether286 that is coupled to ends280 and282. Various exemplary methods of coupling thetether286 to each of theends280 and282 of the longitudinal member are described in further detail below with reference toFIGS. 43-46.
• Referring again toFIG. 41A, thetether286 is shown in a slack position. The longitudinal member is illustrated to bend inFIG. 42A from anoriginal position290 to asecond position292, the longitudinal member being fixed atend293. The displacement (d)291 of the bendingend296 results from the externally applied bending force (f)292. As the longitudinal member bends, thetether286 ofFIG. 41A becomes taught at a level of displacement (dt)295 ofFIG. 42B.FIG. 42B is a graph illustrating displacement (d) of the longitudinal member as a function of externally applied bending force (f). The increase in bending resistance (i.e. reduced displacement in response to increasing force) serves to limit the bending range of the longitudinal member to (d_t)295, and thereby limit the bending range of the spinal stabilization system, beyond which further bending of the spine is limited.
• FIG. 41B Illustrates a cross-sectional view of an embodiment with a longitudinal member as inFIG. 41A, except thattether286 is attached at a position offset from central axis382 of the longitudinal member, thereby differentially limiting the bending range differently in different bending directions because the tether becomes taught at angularly dependent magnitudes of displacement (d) ofFIG. 42A, thereby directionally limiting the bending range of flexible spinal stabilization system beyond which further bending of the spine is limited.
• FIG. 41C illustrates a cross-sectional view of an embodiment with a longitudinal member as inFIG. 41B, except that thetether290 is pre-tensioned resulting in a longitudinal member that is bent in the absence of an externally applied force, so that the longitudinal member is pre-shaped to conform to a curved region of a spine. The directionally limited bending range discussed above is also a feature of the embodiment illustrated in41C, except that displacement of the longitudinal member is substantially limited in one direction for selectively stabilizing or adjusting deformities of the spine.
• FIG. 43 shows a cross-sectional view of an embodiment of a longitudinal member as inFIG. 41A except that one end oftether308 is coupled to anadjustable member316. In this embodiment,adjustable member316 is a cylindrical piece with an externally threadedsection312 that mates with an internally threadedsection303 of anend302 of the longitudinal member. Tether308 is non-rotatably secured to end300 of the longitudinal member. Slot314 ofadjustable member316 is exemplary of a screwdriver slot or internal hex for axially rotatingadjustable member316. Rotating slip joint317 permitsadjustable member316 to axially rotate whiletether308 does not rotate, while transmitting axially directed force fromadjustable member316 to tether308, allowing the application of compression or tension to tether308 by rotationally adjustingadjustable member316, resulting in axial displacement ofadjustable member316. This provides an easy, reversible way to adjust the tension on thetether308. As shown inFIG. 41B, theadjustable member314 can be positioned offcentral axis283 to provide different bending characteristics of the longitudinal member in different bending directions as discussed above in relation toFIG. 41B, or to additionally provide a bend in the longitudinal body as discussed above in relation toFIG. 41C.
• FIG. 44 shows a cross-section of a longitudinal body for another embodiment as inFIG. 43, except that inFIG. 44, thetether308 is non-rotatably attached to anadjustable member313 having external threads thereon. A rotating slip joint319 permitsadjustable member313 to axially rotate together withtether308, while axially anchoringtether308 to end300 of the longitudinal member, allowing the application of compression or tension to tether308 by rotationally adjustingadjustable member313. This provides an easy, reversible way to adjust the tension on the tether.
• FIG. 45 shows a cross-section of yet another embodiment. In thiscase tether308 is non-rotatably anchored to end300 of the longitudinal body, and extends beyond theend302 of the longitudinal body to an externally threadedsection315. Anexternal nut318 has an internally threaded section configured to mate with the externally threadedsection315 and may, when torqued,abut end302, thereby applying tension totether308. Theexternal nut318 is exemplary of a locking member for securing the threadedsection315 in a fixed position after a desired tension on thetether308 has been achieved. Alternately, awasher320 may be interposed betweennut318 and end302. Thewasher320 may be a plain washer to eliminate wear and rotational friction between the adjoining surfaces ofend302 andnut318, or it may be a locking type washer to resist the rotation ofnut318 relative to end302 and prevent inadvertent loosening. Alternately, thewasher320 may be a combination of the two types of washers. Locking washers can come in a simple split ring configuration or a more elaborate design, all of which are well known in the mechanical art.
• FIG. 46 illustrates a perspective view of a longitudinal member similar to the embodiment shown inFIG. 45.
• The longitudinal members shown inFIG. 41 andFIGS. 43 through 46 are fabricated of a biocompatible material, suitable for implantation in the human body as discussed above. Additionally theadjustable members316 and313 ofFIGS. 43 and 44, respectively, as well thetether308,nut318, andoptional washer320 ofFIGS. 45 and 46 are made of such biocompatible material as they may also come in contact with body tissues and fluids when implanted.
• The tethers (286 and290 ofFIG. 41, and308 ofFIGS. 43 through 46) may further assume structural forms such as (i) wires, multi-wire bundles, fibers, multi-fiber bundles, braided structures, ribbons, and multi-ribbon bundles that are suitable for tension, or (ii) solid and/or hollow rods of various cross sections that are suitable for compression or tension, as desired to adjust the spinal stabilization system.
• In a further embodiment, as illustrated inFIG. 47, the longitudinal member need not be hollow, and thetether308 is attached externally to ends300 and302 of the longitudinal member. Thetether308 may be attached in accordance with known suitable means and techniques. In one embodiment, the attachment includes non-rotatable attachments, such as weldments. In other embodiments, thetether308 may be attached via rotatable attachment means such as those described above (e.g., slip joints) or other techniques such as ball and socket joints, etc. Placement of one ormore tethers308, at various locations around the circumference of the longitudinal member can provide directional limits to bending as well as limit longitudinal extension of the longitudinal member. Alternatively, a tether attached externally at an acute angle to the long axis of thelongitudinal member308acan further limit rotation of the longitudinal member.
• Various embodiments of the invention have been described above. However, those of ordinary skill in the art will appreciate that the above descriptions of the preferred embodiments are exemplary only and that the invention may be practiced with modifications or variations of the devices and techniques disclosed above. Those of ordinary skill in the art will know, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such modifications, variations and equivalents are contemplated to be within the spirit and scope of the present invention as set forth in the claims below.

Claims (20)

1. A connection unit for use in a spinal stabilization device comprising a longitudinal member having first and second ends that are configured to be secured to a patient's spine using at least two securing members, a flexible section in between the first and second ends, and at least one tether that is fixed to the longitudinal member at the first and second ends, the at least one tether having enough slack to allow bending or extension of the longitudinal member up to a point that the tether becomes taught, thereby resisting further bending or extension.

2. The connection unit ofclaim 1 wherein the longitudinal member is configured in the shape of a cylindrical rod.

3. The connection unit ofclaim 1 wherein the longitudinal member is hollow.

4. The connection unit ofclaim 3 wherein a cavity of the hollow longitudinal member includes the at least one tether that is fixed to the longitudinal member at the first and second ends.

5. The connection unit ofclaim 1 wherein the longitudinal member comprises a material that is selected from at least one of a group of known, bio-compatible materials consisting of metals, metal alloys, organic polymers, natural resins, synthetic resins, thermoplastics, elastomers and composite materials.

6. The connection unit ofclaim 1 wherein the at least one tether comprises a material that is selected from at least one of a group of known flexible, materials consisting of metals, metal alloys, organic polymers, natural resins, synthetic resins, thermoplastics, elastomers and composite materials.

7. The connection unit ofclaim 1 wherein the at least one tether comprises a structure that is selected from a group of known structures consisting of fibers, multi-fiber bundles, wires, multi-wire bundles, ribbons, multi-ribbon bundles, rods, and multi-rod bundles.

8. The connection unit ofclaim 1 wherein the at least one tether is pre-tensioned to a desired degree of tautness in at least one orientation relative to the longitudinal axis of the connection unit.

9. The connection unit ofclaim 1 wherein the longitudinal member is hollow and the at least one tether is mounted offset from a longitudinal center axis of the hollow longitudinal member to allow for different ranges of bending of the hollow longitudinal member in different directions of bending.

10. The connection unit ofclaim 9 wherein the at least one tether is pre-tensioned to make the hollow longitudinal member bend in the absence of external bending forces.

11. A connection unit for use in a spinal stabilization device comprising a hollow longitudinal member having first and second ends that are configured to be secured to a patient's spine using at least two securing members, a flexible section in between the first and second ends, and at least one tether positioned within a cavity of the longitudinal member, wherein a first end of the at least one tether is coupled to an adjustable coupling member at the first end of the longitudinal member, and a second end of the at least one tether is coupled to the second end of the longitudinal member.

12. The connection unit ofclaim 11 wherein the longitudinal member is configured in the shape of a cylindrical rod.

13. The connection unit ofclaim 11 wherein the adjustable coupling member is an externally threaded screw member configured to mate with an internally threaded section of the first end of the hollow longitudinal member, the screw member being capable of rotation to adjust its position along a longitudinal axis of the hollow longitudinal member, thereby adjusting an axially directed tension on the at least one tether.

14. The connection unit ofclaim 13 wherein the screw member is coupled to the at least one tether with a slip joint that allows axial rotation of the screw member without rotating the at least one tether and maintains the axially directed tension on the tether by the screw member.

15. The connection unit ofclaim 13 wherein the screw member is rigidly fixed to the first end of the at least one tether, and the second end of the at least one tether is coupled to a slip joint located at the second end of the longitudinal member such that the slip joint allows rotation of the at least one tether while maintaining the axially directed tension on the at least one tether.

16. The connection unit ofclaim 11 wherein the adjustable coupling member comprises a material that is selected from at least one of a group of known, bio-compatible materials consisting of metals, metal alloys, organic polymers, natural resins, synthetic resins, thermoplastics, elastomers and composite materials.

17. The connection unit ofclaim 11 wherein the hollow longitudinal member comprises a material that is selected from at least one of a group of known, bio-compatible materials consisting of metals, metal alloys, organic polymers, natural resins, synthetic resins, thermoplastics, elastomers and composite materials.

18. The connection unit ofclaim 11 wherein the at least one tether comprises a material that is selected from at least one of a group of known flexible, materials having controlled extensibility responsive to tensile stress consisting of metals, metal alloys, organic polymers, natural resins, synthetic resins, thermoplastics, elastomers and composite materials.

19. The connection unit ofclaim 11 wherein the at least one tether comprises a structure that is selected from a group of known structures consisting of fibers, multi-fiber strands, wires, multi-wire strands, ribbons, multi-ribbon strands, rods, and multi-rod bundles.

20. The connection unit ofclaim 11 wherein the at least one tether is mounted offset from a longitudinal center axis of the hollow longitudinal member to allow for different ranges of bending of the hollow longitudinal member in different directions of bending.

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