Posterior functional dynamic stabilization system

Abstract

A spinal stabilization unit (10) comprising: a flexible coupler (20) with a flexible coupler body (22), a range-of-motion limiting mechanism configured to control a certain degree of flexion, compression, and extension of the flexible coupler (20), the range-of-motion limiting mechanism comprising a tapered bushing (90) extending internally from a first end of the flexible coupler body (22) and having a narrowed distal opening (98), and a needle (100) with an elongated body (102) having an enlarged head region (104) and shoulder region (106) extending from a opposite end of the flexible coupler body (22), the needle (100) being configured to be received within the tapered bushing (90) and to cooperate with the bushing (90),to form an expansion and compression stop within the flexible coupler body (22), wherein the enlarged head region (104) of the needle (100) is arranged within the tapered socket (90) and is dimensioned such that the enlarged head region abuts the wall of the narrowed opening (98) when the flexible coupler (20) is extended or bent, and the socket (90) abuts the second end of the flexible coupler (20) when the flexible coupler (20) is compressed; and a pair of arms (30, 40), wherein the arms are located at opposite ends of the flexible coupler (20) for receiving bone anchors (50) to secure the flexible coupler (20) to the bone.

Description

This patent application claims priority to United States Provisional Patent Application No. 60 / 869342 filed on December 10, 2006, and United States Provisional Patent Application No. 60 / 914360 filed on April 27, 2007. Both applications are incorporated in their entirety into the present application.REGIONThe present invention relates to apparatus and methods for treating spinal diseases, and more particularly to spinal stabilization systems for controlling or limiting relative movement between vertebrae.BackgroundThe spine includes a series of joints known as motion segments. Each unit represents the smallest component of the spinal column which exhibits a kinematic behavior characteristic of the entire spinal column. The motion segment may curve, expand, bend sideways, and slide. The components of each motion segment include two adjacent vertebrae, the associated apophysis joints, an intervertebral disc, and connective tissue associated with the ligaments. Each component of the motion segment contributes to the mechanical stability of the joint. The discs separating the adjacent vertebrae provide, for example, strength and help reduce relative movement of the vertebrae during bending, extension, axial rotation and lateral bending.If the components of a motion segment shift from their position or are damaged due to trauma, mechanical injury, or disease, severe pain and further destabilizing injury may occur to other components of the spinal column. In a patient with degenerative disc disease (DDD), a damaged disc may provide potentially insufficient strength. One possible result is excessive relative movement of the vertebrae under load on the spine. This causes pain and further damages the intervertebral disc. Depending on the severity of the structural changes, the treatment may include compound, discectomy, and / or laminectomy.Present day treatment procedures often involve the joining of the unstable motion segments by the removal of adjacent tissue. For many reasons, a compound may be an undesirable treatment method. For example, connection can result in permanent, rigid fixation with irreversible loss of the range of motion at the connected sites of the spine. Furthermore, the loss of mobility at the connected sites transfers the load to other adjacent moving parts. This may cause or speed up degeneration of these parts. In addition, the compound often does not alleviate some or all of the pain.It would therefore be desirable to provide a spinal stabilization system that is sufficiently dynamic-functional to accomplish the stress distribution of the treated spinal column. It would further be desirable to provide a system that would allow for near normal movement, mimic the physiological response of a healthy part of the movement, and provide relief of pain.US 2006 / 0 189 984 A1 discloses a system and a method which provide a relative movement restriction between two vertebrae by means of a spring-based configuration.Connecting elements for dynamically fixing the spinal column by means of a body made of a flexible polymer are likewise known from US 2006 / 0 142 758 A1.Furthermore, damping elements are described in WO 2003 / 047 442 A1, which can be adapted to the respective patient by a predefined prestressing force of a spring.A spring-based damping is likewise known from US 2003 / 055 427 A1, wherein an axial movement of two vortices is limited by a piston and a spring.Furthermore, EP 1 072 228 A1 discloses an implantable device for connecting at least two vertebrae, which device is used in particular for treating displaced vertebrae in the case of scoliosis or lordosis.SUMMARYThe present disclosure provides a dynamic functional stabilization unit and system for treating spinal instability due to, e.g., injury, trauma, or disc degeneration (DDD). Each unit and the system in its entirety is configured to control flexion, extension and translation of the affected vertebrae. By restoring normal function, the vertebral parts are stabilized. This is accomplished by providing a unit and system that allows lateral bending, axial compression, rotation, front segmental height adjustment, and rear segmental height adjustment. The unit and system provide sufficient segmental strength, but also control the range of motion to stabilize the segments of the spinal column. In use, the system simulates the natural motion of the normal spine. Furthermore, the system is configured to allow adjustments over time, corrective interventions (e.g., connection), and percutaneous implants.In accordance with an exemplary embodiment, a dynamic-functional spinal stabilization system is provided. The system may include a flexible coupler and a cylindrical body, including one or more notches in the wall of the cylindrical body. The system may further include a pair of gripping arms for connection to the bone anchors. The arms are located at opposite ends of the coupler. The flexible coupler may also include an internal motion limiting mechanism configured to limit motion of the flexible coupler upon bending, compression, and tension. The system may further include a pair of bone anchors configured for cooperation with the gripping arms for connection to bone tissue.In accordance with another exemplary embodiment, the system further includes a rigid coupler having a pair of gripping arms for connection to bone anchors. As with the flexible coupler, the arms may be located at opposite ends of the coupler. However, this coupler does not allow extension or compression as does the flexible coupler. The coupler rather promotes connection by preventing movement at that location.Also provided is a method of spinal treatment. This method may also include attaching a first bone anchor to a vertebra and a second bone anchor to an adjacent vertebra. A flexible coupler may then be attached to the first and second bone anchors. The flexible coupler may include a cylindrical body having one or more notches in the wall of the cylindrical body and an internal motion limiting mechanism configured to limit motion of the flexible coupler during bending, compression, and tension.Also provided is a method of percutaneously implanting the system which minimizes tissue damage and facilitates insertion and also a number of instruments for using this method. The method may include making at least one incision over at least two of the adjacent vertebrae to be treated, and placing at least two wires such that each wire individually contacts a pedicle of at least one vertebra. A screw may be mounted in each vertebra and the distance between the screws inserted into the two adjacent vertebrae is measured. A flexible coupler for attachment to the screws is selected and the length of the flexible coupler is adjusted based on the measured distance.It is expressly understood that both the foregoing general description and the following detailed description are examples and explanations only and do not constitute the entire disclosure as set forth in the claims.The accompanying drawings, which form a part of this specification and are incorporated in and constitute a part of this specification, illustrate some embodiments of the disclosure and together with the description serve to explain the principles of this disclosure.Additional objects and benefits of the disclosure will be set forth in part in the description which follows, or may be learned by the practice of the disclosure. The objects and advantages of this disclosure will in fact be realized and attained by the elements and combinations particularly pointed out in the appended claims.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 shows a side perspective view of an implanted dynamic functional stabilization system. FIG. 2 is a top view of the implanted dynamic functional stabilization system of FIG. 1 and includes two stabilization units on opposite sides of the spinal column. FIG. 3 is a rear view of the system of FIGS. 1-2. FIG. 4A shows a perspective view of a stabilization unit of the system of FIGS. 1-3. Figure 4B shows a side view of a portion of a flexible coupler used in the stabilization unit of Figure 4A. FIG. 4C shows a top view of the flexible coupler of FIG. 4B. Figure 5A shows a cross-section of the unit of Figure 4A. FIG. 5B is an enlarged view of a portion of the stabilization unit of FIG. 4A. FIG. 6 shows an enlarged view of the flexible coupler of FIGS. 4B-4C. FIG. 7A shows a perspective view of a portion of the flexible coupler of FIGS. 4B and 4C. FIG. 7B shows a perspective view of a portion of the flexible coupler portion of FIG. 7A. FIG. 8A shows a cross-section of the flexible coupler of FIG. 4B in the rest position. FIG. 8B shows a cross-section of the flexible coupler of FIG. 4B in a fully deployed state. FIG. 8C shows a cross-section of the flexible coupler of FIG. 4B in a fully compressed state. FIG. 8D shows an enlarged view of the flexible coupler of FIG. 8A in the rest position. FIG. 9A shows a perspective view of another embodiment of an implanted dynamic-functional stabilization system. FIG. 9B shows an enlarged view of the implanted system of FIG. 9A. Figure 10 shows a side view of a portion of the system of Figures 9A-9B. FIG. 11A shows a perspective view of a rigid coupler that may be used with the stabilization systems of the present disclosure. FIG. 11B shows a cross-section of the rigid coupler of FIG. 11A running along line A-A. FIG. 11C shows a side cross-section of an alternative embodiment of a rigid coupler that may be used with the stabilization system of the present disclosure. FIG. 12 shows a perspective view of a modular multi-segmental stabilization system, according to another embodiment of the disclosure. FIG. 13 shows a perspective view of a wire pattern and K-wires used to facilitate implantation of the spinal stabilization systems of the present disclosure. FIG. 14A shows a perspective view of a number of studs used to facilitate implantation of bone anchors with the methods of the present disclosure. FIG. 14B shows a partially cut-away view of a shoulder rod of FIG. 14A connected to a bone anchor. FIG. 15 shows a perspective view of a grip compass. FIG. 16 shows a perspective view of another set of tie rods, in accordance with the present disclosure. Figure 17 shows a perspective view of an instrument for adjusting the length of a flexible coupler. FIG. 18A shows a perspective view of a nut used to secure the stabilization units of the present disclosure. FIG. 18B shows a partially cut-away view of the threaded nut of FIG. 18B connected to the insertion instrument of FIG. 19. FIG. 19 is a perspective view of an insertion instrumentDESCRIPTION OF THE EMBODIMENTSThe present disclosure presents a dynamic-functional stabilization unit and a system that includes dynamic-functional stabilization units for treating spinal instability. The present disclosure further presents minimally invasive methods for implanting spinal stabilization systems, as well as instruments, to facilitate the use of these methods.The assembly, system, and methods of the present disclosure may be used to treat spinal diseases caused by, for example, injury, trauma, or disc degeneration (DDD). The stabilization unit and systems comprising such units are configured to restrict flexion, extension and translation of the affected unstable vertebrae, stabilizing the vertebral parts and restoring normal function. This is accomplished by providing a unit and system that allows lateral bending, axial compression, rotation, anterior segmental height adjustment, and posterior segmental height adjustment on the spinal column. The unit and system provide sufficient segmental strength within the patient's neutral or active zone, but they also limit or control the range of motion outside a desired zone. In use, the system limits the natural movement of the normal spine. Furthermore, the system is configured to allow changes over time, corrective interventions, and percutaneous implants.Referring now to the drawings, Figure 1 shows one embodiment of a dynamic stabilization system 8 implanted between adjacent vertebrae 2,4. Figure 2 shows a top view of an implanted dynamic-functional stabilization system and Figure 3 shows a rear view of the system 8 of Figures 1-2. As shown, the system 8 may include one or more flexible stabilization units 10 that may be implanted on a posterior section of the spine to stabilize the affected vertebrae 2, 4.As shown in FIG. 4A, each dynamic stabilization unit 10 may include a flexible coupler 20 connected to at least one bone anchor 50, such as a pedicle screw or a bone screw. The coupler 20 may include a flexible body 22 including notches 24 and apertures 26. As shown in Figures 4B-4C, flexible body 22 may include at one end a gripping arm 30 having an opening 32 for insertion of a bone anchor 50, and at the opposite end a second gripping arm 40, also having an opening 33 for a bone anchor 50. gripping arms 30, 40 may be molded in one piece with body 22 or may be detachably connected to body 22. For example, one end of the gripping arm 40 may be threaded for connection to the flexible body 22, such as by a bushing 90 located within the flexible body 22, as shown in Fig. 6.Each gripping arm 30, 40 of the coupler 20 may include a concave-shaped bulge 34, 44 on one side; they are configured to snap into a semi-spherical ball bearing 60, as shown in FIGS. 5A-5B and 6. The ball bearing 60 may have a through hole and may fit over the bone anchor 50. In one embodiment, bone anchor 50 may include an elongated threaded shank 52 that extends to a flange 56 that connects to a head portion 54 upon which ball bearing 60 may be placed. The flange 56 may further include indentations 57 for easier anchoring to bone tissue, thus reducing detachment of the anchor 50 over time. The bone anchor 50 may be, for example, a pedicle screw. Preferably, bone anchor 50 may be inserted through a cannula to enable assembly 10 or system 8 to be applied percutaneously. With the concaved indentations 34, 44, the gripping arms can slide or rotate with respect to the ball bearing 60. Thus, the gripping arms 30, 40 are allowed to move relative to the bone anchor 50. Other suitable structures may be used to connect the flexible body 22 to the bone anchors 50 with relative movement therebetween.As further shown in FIGS. 5A, 5B, and 10, a washer 70 may be placed on the screw 50 and against flange 56 or nut 80. The washer 70 may be configured and shaped to abut the ball bearing 60. An assembled dynamic stabilization unit 10 would further include a threaded nut 80 that is threaded onto the head portion 54 of the screw 50 to securely connect the components together, as shown in FIGS. 4A and 5A.Each functionally dynamic stabilization unit 10 is configured to allow a range of motion or deflection of 1.5 to 3.00 mm, the range of deflection being measured from the center of a first pedicle screw coupled to a first gripping arm 30 to the center of a second pedicle screw coupled to a second gripping arm 40. This deflection or this range of movement can be achieved, for example, by means of rotation, expansion or translation.FIG. 6 shows an enlarged view of the flexible coupler of FIGS. 4A-4C. As shown, in some embodiments, one of the gripping arms 40 may be removably attached to the coupler 20. In one embodiment, the coupler 20 may include a threaded aperture 28 to securely secure the second gripping arm 40 and other components. Within the flexible coupler 20 may be a bushing 90 having an opening 92 at one end and a threaded rim 94 around the opening 92 included for bolting to the coupler body 22. The needle 100 may include an elongated body 102 having an end thread. The body 102 terminates in a semi-spherical head region 104 and includes a torso or shoulder region 106. In cooperation, the bushing 90 and the needle 100 provide a stop for extension and compression within the coupler body 22, reducing the range of motion of the flexible coupler 20 at the neutral or active zones of the patient.Ring 92 of bushing 90 is adapted to be threadably engaged with end threads 46 of removable second gripping arm 40. The overall length of the coupler 20 can be adjusted by changing the depth of thread threading of the second gripping arm 40 into the bushing 90 (e.g., by changing the number of revolutions of arm 40 into the bushing 90. As shown, the end thread 46 of the removable second gripping arm 40 may extend to a number of compressible finger projections 43, each projection 43 terminating at a flanged lip 47. The flanged lip 47 serves as a closing mechanism and prevents the second gripping arm 40 from coming off the bushing 90 after attachment. The end thread 46 may further include a boss 48 to house an elastomeric plug 110, as shown in FIG. 8C. The elastomeric plug 110 may be made of a soft, compliant plastic material, such as silicone, polyethylene, or polyetheretherketone (PEEK). Since the second removable gripping arm 40 is threadedly connected to the socket 90, the plug 110 interacts with the threaded aperture to reduce the clearance between the arm 40 and the socket 90, other suitable structures may be used which allow adjustment of the length of the flexible body while controlling the amount of compression and extension of the flexible body. For example, a gripping arm may be mounted to provide a friction fit. A telescoping link or ratchet mechanism may also be used.As shown in detail in FIGS. 7A and 7B, in one embodiment, the coupler body 22 includes, for example, a cylindrical body comprised of a series of ring-ring units 22A. The series of ring assemblies 22, when connected together, form a stepwise series of slots 24, each notch 24 terminating at an opening 26 of the flexible body 22. In some embodiments, the series of ring units 22A may be made of a single piece such that the units 22A are integrally connected together. For example, in one embodiment, the ring units 22A may be etched or cut from a single tubular piece. In other embodiments, one or more ring units 22A may be manufactured individually and then stacked upon each other. The ring units 22A stacked on each other may be joined together by welding or mechanical joints, for example.It should be noted that the degree of strength of the coupler body 22 may vary depending on the size, width, distance, or angle between two adjacent notches 24 and the number of units 22A that form the coupler body 22. Furthermore, one or more units 22A may be made of different materials to vary the mechanical properties of the body 22. Furthermore, the dimensions of the units 22A, notches 24, and apertures 26 may be varied within a single body 22.FIGS. 8A-8D show an embodiment of a fully assembled flexible coupler 20 in the quiescent state (FIGS. 8A and 8D ), a fully deployed or deflected state (FIG. 8B ), and a fully compressed state (FIG. 8C ). In the rest state, shown in FIG. 8A and an enlarged view in FIG. 8D, needle 100 and bushing 90 are unlocked (i.e., they are free of drag forces or obstructions). In the fully deployed or deflected state (FIG. 8B ), the needle head 104, having a cross-section greater than the width of the narrowed opening 98, abuts the narrowed opening 98 of bushing 90 and thus prevents the flexible coupler body 22 from excessively expanding. In the fully compressed state (Fig. 8C), the end of bushing 90 with restricted opening 98 abuts the inner edge of first gripping arm 30, as shown. The cooperation of the bushing 90 and needle 100 in the coupler body 22 provides a deflection-compression-stop mechanism to control or limit the range of motion provided herein, and thus prevents injury or damage not only to the affected vertebral parts, but also to the dynamic stabilization unit itself. Other types of supporting elements, such as a telescoping element or an internal piston, may be used to control or limit the range of motion of coupler body 22.As mentioned above, the dynamic-functional stabilization unit 10 may be used alone to stabilize portions of the fluidizing acid. Furthermore, more than one unit 10 may also be used in combination, if desired, to provide a multi-level dynamic-functional stabilization system 12, as shown in FIGS. 9A and 9B. The multi-level dynamic functional stabilization system 12 may include two or more units 10 connected together.FIG. 10 shows a side view of the system of FIGS. 9A-9B. As shown, the system 12 includes a pair of flexible couplers 20 that are aligned. The couplers 20 are placed so that the first gripping arm 30 of each coupler 20 is positioned around a ball bearing 60, with a bone anchor 50 and nut 80 securing the combination. It is believed that more than two couplers 20 can be combined in this manner, and either the first 30 or second 40 gripping arms of each individual coupler can be combined with the first 30 or second 40 gripping arms of another coupler 20 at a bone anchor 50. Any number of couplers 20 may be implanted on the patient's spinal column, either along one side or on both sides. Furthermore, the units 10 may have different mechanical properties depending on the pathology and anatomy of the patient.In some implementations, the stabilization systems of the present disclosure may allow connection of one or more motion segments of the spinal column, along with dynamic-functional stabilization of other motion segments. To this end, the stabilization system may include a rigid connection-supporting coupler 101. For one possible example, see FIG. 11A. The rigid coupler 101 may be configured for use with the bone anchors 50, ball bearings 60, and washers 70 (see previous description). As shown, the rigid coupler 101 includes two components 122, 124, each terminating in a respective gripping arm 130, 140, similar to the flexible coupler 20 already described.As further shown in FIG. 11B, the two components 122, 124 may be connected together so as to conform to the length of the rigid coupler 101. For example, the components 122, 124 may include threaded surfaces and the length of the rigid coupler 101 may be adjusted by rotating one component 122 relative to the other component 124, similar to the process already described in adjusting the length of the flexible coupler 20. Each of the gripping arms 130, 140 may also include a concave cavity 134, 144 on a bottom surface configured to abut a semi-spherical ball bearing 60. Thus, the implantation of the rigid coupler 101 to the bone anchors 50 is similar to the implantation of the flexible coupler 20, as previously described.As further shown in FIG. 11C, an alternative embodiment of a rigid, connection-supporting coupler 201 may be provided. The rigid connection assist coupler 201 is similar to the rigid coupler 101 except that threaded surfaces are not used on the components to adjust the length of the coupler 201. The rigid coupler may be configured for use with bone anchors 50, ball bearings 60, and washers 70 in the form described above. As shown in the figure, the rigid coupler is comprised of two components, 222 and 224, each of which extends to a respective gripping arm 230, 240 in a manner similar to that previously described for the flexible coupler 20. Both arms 230, 240 have an opening (not shown) for coupling to a bone anchor 50 in a similar manner as previously described for flexible coupler 20. Each of the gripping arms 230, 240 may also have a concave cavity 234, 244 at the bottom side, respectively, which is configured to abut a semi-spherical ball bearing 60.The first component 222 and the second component 224 may be moved relative to each other to thereby facilitate adjustment of the length of the coupler 201. Instead of the threaded surfaces, the component 222 may include a cavity 226 configured to receive a fastener 230 securing the first component 222 relative to the second component 224. Since the first and second components do not have threaded surfaces, the two are moved relative to each other by sliding the components rather than by rotating them. In such an embodiment, the surgeon may adjust the length of the rigid coupler 201 within him as desired.The closure element 230 may be any suitable closure element such as a screw or nut. For example, a fastener 230 may be a breakaway threaded nut, a first portion of which is configured to fixedly couple the portion 226 to the component 222 to thereby fix the position of the first component 222 relative to the second component, and a second portion configured to use an insertion device to screw the first portion to the rigid coupler. The second portion of the breakaway nut may include a breakaway portion having a thinner wall or region of lower yield strength material and configured to break when sufficient torque is applied (e.g., when the nut 230 has been sufficiently tightened). The inner surface of the cavity 226 and the outer surface of the closure member 230 may be threaded to ensure coupling of the cavity 226 to the closure member 230.As mentioned above, the stabilization system may include both dynamic functional flexible couplers 20 and fixed couplers 101. Thus, a modular system is presented which allows the combination of motion maintenance and connection at certain parts of the patient's spinal column. By making the fixed coupler 101 and the flexible coupler 20 interchangeable in the system, greater flexibility is provided to the surgeon to accommodate the particular needs of the patient. Thus, a portion of the spinal column may have functional dynamic stabilization (i.e., non-connection), while an adjacent portion has fixed segmental attachment (i.e., connection).Figure 12 shows a multi-segmental system 12 consisting of three independent stabilization units 10a, 10b, 10c using flexible couplers 20a, 20b and a rigid coupler 101. The flexible couplers 20a, 20b of units 10a and 10c increase the segmental strength of the subject moving part and limit the range of movement during flexion, extension, lateral bending and rotation, while the movement is maintained. By selecting a coupler 20a, 20b of appropriate size, the posterior segmental height can also be adjusted. Furthermore, the fixed connection-supporting coupler 101 of unit 10b provides a fixed segmental attachment and thus supports the connection. It uses the same type of bone anchors 50 and instruments.The modular system 12 provides a variety of advantages. For example, initially an implanted system may contain only dynamic-functional flexible couplers 20 connected to vertebrae by bone anchors 50 as described. However, it may become desirable as a result to combine one or more levels already treated due to progression of the disease, unaltered pain, other symptoms, or other changes in the condition of the patient. Thus, in subsequent procedures, the surgeon may simply replace an already implanted flexible coupler with a rigid coupler 101 and may use the same bone anchors.As mentioned above, the devices and systems of the present disclosure may be implanted by a minimally invasive procedure that preserves muscles. Such methods may involve percutaneous procedures or a series of small incisions which minimize tissue damage.Figures 13-19 show exemplary embodiments of insertion instruments which may be provided individually or as a set together with the system. In an exemplary method of the present system, a number of K-wires 200 are inserted into the pedicle of the patient's spinal column. The K-wires 200 can be inserted through a series of small incisions in the back of the patient. As further shown in Figure 13, a wire pattern 202 may be provided to aid the surgeon in placing the incisions and K-wires 200. The wire pattern 202 may include prefabricated apertures 204 that conform to the pedicles of the patient's spinal column as shown. The apertures 204 may be arranged on both sides of a line together with both pedicles of the vertebrae to be treated. The pattern can be presented in various sizes to accommodate patients having different distances between pedicles.After the insertion of K-wires 200, the bone anchors 50 can be guided in a cannula over the K-wires 200. By means of a series of extension rods 220a, 220b, 220c as shown in Figure 14A, the bone anchors can be implanted in the selected vertebra. As shown in Figure 14B, the expansion rods may be attached to the head portions 54 of the bone anchor 50 to allow manipulations of the anchor 50. Furthermore, a dilation sleeve (not shown) may be provided. The dilation rods may be passed through the dilation sleeve so as to reach the site of implantation. After or during implantation of the bone anchors 50, the expansion rods 220 may be used to manipulate the anchors 50 and the secured vertebrae to ensure the full range of motion in the resting state and under load. Such information may be helpful to the surgeon to predict the possible range of corrective motion that is desirable for the affected portion of the spine.A grasping compass 240 as shown in Figure 15 may also be provided with the instrument set. The grip circle 240 may include a pair of pivotable arms 242, 244. Each arm widens into an opening 246, 248 coupled to a finger and ends at an opposite end in a gripping end 250, 252. The pivotable arms 242, 244 may be connected by a leaf spring 254. As shown, the arm ends 242, 244 are configured to provide a measurement of the distance between a pair of adjacent bone anchors 50 using the markings 258 on a plate 256 behind. The gripping ends 250, 252 may be configured to hold a portion of the ball bearing 60 of each bone anchor 50. Thus, the grasping circle 240 can function even when the bone anchors 50 are not placed parallel to each other or at a particular angle to each other.FIG. 16 shows various extension rods 260 configured to be coupled to other components of the anchor, such as ball bearings 60, washer 70, or nut 80Once the bone anchors 50 are in place and the distance between a pair of adjacent bone anchors 50 has been established, the surgeon may select a suitably sized dynamic flexible coupler 20 or a rigid connection assisting coupler 101 to place it between the anchors 50. A height adjustment instrument 270 similar to that shown in Figure 17 may be used to ensure that the length of the coupler prior to insertion is correct. As shown, the length adjustment instrument 270 may include a body 272 having handles 271 between which a coupler 20, 101 may be held. Within the body 272 is a spring mechanism which exerts unequal force on one of the handles 271. The spring mechanism can be controlled by turning a knob 280. The coupler 20, 101 is rotated and as a result its length is adjusted. The body 272 may further include a window 278 having markings 276 indicating the length of the coupler. Although a flexible coupler 20 is shown, it is contemplated that the length adjustment instrument 270 may also be used with a rigid coupler 101.The appropriate size coupler 20, 101 is then drawn down the K-wires and onto the ball bearing 60 of the bone anchors 50. Nuts 80 may then be used to securely attach the couplers 20, 101. In some implementations, the nuts 80 may have certain features that prevent excessive or insufficient tightening. For example, Figure 18A shows an exemplary embodiment of a mating nut 180 having a releasable portion 182 that connects a lower anchor connectable portion 186 to an upper portion 184. The releasable portion 182 has a thinner wall or region of weaker material and is configured to break off when sufficient torque is applied (i.e., when nut 80 has been tightened sufficiently).Nut 180 can be inserted by the same minimally invasive procedure used to implant bone anchors 50 and couplers 20, 101. For example, FIG. 19 shows an example insertion instrument 290 suitable for inserting nut 180. The insertion instrument 290 includes an elongated body 292 that extends from the handle portion 294 to a nut fitting 296 at an opposite end. The fitting 296 may be configured to be securely fastened to the nut of the upper part 184 as shown in FIG. 18B. The elongated body 292 may be inserted with a nut into a predetermined access location to secure the nut 180 to a bone anchor 50. Upon sufficient tightening, the nut 180 will break off the releasable portion 182. This results in the lower portion 186 remaining on a bone anchor and the upper portion 184 being able to be pulled out.The surgeon may then choose to repeat this process at an adjacent location until all affected sites of the patient's spinal column have been treated. The entire process can be carried out percutaneously and / or with minimal disturbance to the surrounding tissue.Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specifications and by application of the invention described herein. The specifications and examples are to be considered as exemplary only. The true scope and true scope of the invention are set forth in the following claims.

Claims

A spinal stabilization unit (10) comprising: a flexible coupler (20) having a flexible coupler body (22); a motion bandwidth limiting mechanism configured to control a degree of flex, compression and extension of the flexible coupler (20), wherein the motion bandwidth limiting mechanism comprises a tapered hub (90) extending internally from a first end of the flexible coupler body (22) and having a narrowed distal opening (98); and a needle (100) having an elongated body (102) with an enlarged head region (104) and shoulder region (106) extending from a mutual end of the flexible coupler body (22), wherein the needle (100) is configured to be received within the tapered hub (90) and cooperate with the hub (90), To form an extension and compression stop within the flexible coupler body (22), wherein the enlarged head region (104) of the needle (100) is disposed within the tapered hub (90) and dimensioned such that the enlarged head region abuts the wall of the narrowed opening (98) when the flexible coupler (20) is extended or bent and the hub (90) abuts the second end of the flexible coupler (20) when the flexible coupler (20) is compressed; and a pair of arms (30, 40), wherein the arms for receiving bone anchors (50) are at opposite ends of the flexible coupler (20) to secure the flexible coupler (20) to the bone.The assembly of claim 1, wherein at least one of the arms of the flexible coupler (30, 40) is attached to the flexible coupler at a threaded connection.The unit of claim 1, wherein the flexible coupler body (22) is stretchable and compressible along the longitudinal axis of the flexible coupler body (22).The unit of claim 1, wherein the flexible coupler body (22) is bendable relative to the longitudinal axis of the flexible coupler body (22).The assembly of claim 1, wherein the flexible coupler body (22) is cylindrical and includes a plurality of elements (22A) forming notches (24) within the flexible body.The unit of claim 1, wherein one of the arms (30, 40) is attached to the flexible coupler (20) by a threaded connection, and the length of the flexible coupler (20) can be adjusted by rotating the arm with respect to the threaded connection.The unit of claim 1, wherein the needle (100) is cooperatively and movably positioned within the hub (90) such that movement of the needle (100) relative to the hub (90) in a first direction defines a range of extension of the flexible coupler (20) and movement of the needle (100) relative to the hub (90) in a second direction opposite the first direction defines a range of compression of the flexible coupler (20).The assembly of claim 1, wherein the anchoring system further includes at least one ball bearing (60) and at least one threaded nut (80, 180).The assembly of claim 1, wherein each arm (30, 40) includes a concave portion (34, 44) having an opening (32, 33), and the anchoring system further includes a semi-spherical ball bearing (60) for each bone anchor (50).The assembly of claim 9, wherein the flexible coupler (20) is movable relative to the plurality of bone anchors (50).The unit of claim 1, wherein the flexible coupler (20) is configured to be movable with respect to the anchoring system.The assembly of claim 1, wherein the anchoring system further includes a plurality of nuts (80, 180), each nut having a narrowed releasable portion (182) configured to break upon application of sufficient torque to the nut.A modular spinal stabilization system (12) comprising: a flexible coupler (20) having a flexible coupler body (22), a pair of arms (130, 140, 230, 240) located at opposite ends of the flexible coupler (20), and a motion bandwidth limiting mechanism configured to control a degree of flex, compression and extension of the flexible coupler (20), wherein the motion bandwidth limiting mechanism comprises a tapered socket (90) extending internally from a first end of the flexible coupler body (22) and having a narrowed distal opening (98), and a needle (100) having an elongated body (102) having an enlarged head region (104) and shoulder region (106) extending from a mutual, second end of the flexible coupler body (22), wherein the needle (100) is configured to be received within the tapered hub (90) and cooperate with the hub (90) to form an extension and compression stop within the flexible coupler body (22), wherein the enlarged head region (104) of the needle (100) is disposed within the tapered hub (90) and is dimensioned such that the enlarged head region abuts the wall of the narrowed opening (98) when the flexible coupler (20) is extended or bent, and the hub (90) abuts the second end of the flexible coupler (20) when the flexible coupler (20) is compressed; a rigid coupler (101, 201) comprising a pair of arms (130, 140, 230, 240) located at opposite ends of the rigid coupler (101, 201) and a fixation system including a plurality of bone anchors (50) configured to cooperate with the arms of the flexible and rigid couplers to secure the couplers to the bone.The system of claim 13, wherein the flexible coupler body (22) includes a cylindrical body portion including one or more notches (24) in a wall of the cylindrical body portion.The system of claim 13, wherein the flexible coupler body (22) is expandable and compressible along the longitudinal axis of the flexible coupler body (22).The system of claim 13, wherein the flexible coupler body (22) is bendable relative to the longitudinal axis of the flexible coupler body (22).The system of claim 13, wherein at least one of the arms (30, 40) of the flexible coupler (20) is connected to the flexible coupler (20) by a threaded connection.The system of claim 13, wherein an arm (30, 40) of the flexible coupler (20) is connected to the flexible coupler (20) by a threaded connection, and the length of the flexible coupler (20) is adjustable by rotation of the arm (30, 40) with respect to the flexible coupler (20).The system of claim 13, wherein the needle (100) is cooperatively and movably positioned within the hub (90) such that movement of the needle (100) relative to the hub (90) in a first direction defines a range of extension of the flexible coupler (20) and movement of the needle (100) relative to the hub (90) in a second direction that is opposite the first direction defines a range of compression of the flexible coupler (20).The system of claim 13, wherein the fixation system further includes a plurality of ball bearings (60) and nuts (80, 180).The system of claim 20, wherein the flexible coupler (20) is configured to be movable relative to the plurality of bone anchors (50).The system of claim 13, wherein the flexible coupler (20) is configured to be movable relative to the fixation system.The system of claim 13, wherein the length of the rigid coupler (101, 201) is adjustable.The system of claim 23, wherein an arm (130, 140, 230, 240) of the rigid coupler (101, 201) is connected to the rigid coupler (101, 201) by a threaded connection, and the length of the rigid coupler (101, 201) is adjustable by rotation of the arm (130, 140, 230, 240) with respect to the rigid coupler (101, 201).The system of claim 13, wherein the fixation system further includes a plurality of semi-spherical ball bearings (60), and wherein the arms (30, 40) of the flexible coupler (20) and the arms (130, 140, 230, 240) of the rigid coupler (101, 201) each have a concave portion (34, 44, 134, 144, 234, 244) with an opening (32, 33, 132) configured to be engageable with a semi-spherical ball bearing.The system of claim 13, wherein the fixation system further includes a plurality of nuts (80, 180) for securing the rigid (101, 201) or flexible coupler (20) to the respective bone anchors (50), each nut having a narrowed releasable portion (182) configured to break upon application of sufficient torque to the nut.The system of claim 13, further comprising a second flexible coupler (20).The system of claim 13, further comprising a second rigid coupler (101, 201).The system of claim 13, further comprising a second flexible coupler (20) and a second rigid coupler (101, 201).

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