Abstract:
A bio-compatible stabilization system includes one or more inserters and a connector for traversing a space between one or more bony structures. The stabilization system is designed to reduce or eliminate stress shielding effects while functioning as a tension band. The connector includes an extendable member and an over-extension limiter that limits extension of the extendable member.

Description:
BACKGROUND 
       [0001]    Severe back pain and nerve damage may be caused by injured, degraded, or diseased spinal joints and particularly, spinal discs. Current methods of treating these damaged spinal discs may include vertebral fusion, nucleus replacements, or motion preservation disc prostheses. Disc deterioration and other spinal deterioration may cause spinal stenosis, a narrowing of the spinal canal and/or the intervertebral foramen, that causes pinching of the spinal cord and associated nerves. Current methods of treating spinal stenosis include laminectomy or facet resection. Alternative and potentially less invasive options are needed to provide spinal pain relief. 
       SUMMARY 
       [0002]    In accordance with one aspect of the present disclosure, an implant for stabilizing bony structures is presented. The implant includes a first end, a second end, and an extendable member connected to the first end and the second end. The extendable member is sized to traverse a space between at least two bony structures. The implant further has an over-extension limiter connected to the first end and the second end, and traversing the space between the at least two bony structures. The over-extension limiter is configured to prevent over-extension of the extendable member. 
         [0003]    In accordance with another aspect, the present disclosure includes an implant system. The implant system includes a connector having a first and a second extendable member. The first extendable member has a first extendibility and the second member has a second extendibility that is less than the first extendibility. The implant system further includes an inserter designed to engage the connector to position the connector adjacent an anchor securable to a bony structure. 
         [0004]    According to another aspect, the present disclosure is directed to a spinal stabilization kit that includes a first bone anchor and a second bone anchor. The kit further includes a connector designed to be anchored to the first bone anchor and the second bone anchor. The connector has a first extendable component and a second extendable component. The second extendable component, when taut, limits farther extension of the first extendable component. 
         [0005]    In accordance with yet another aspect of the present disclosure, a system for stabilizing a spinal motion segment is presented. The system includes a first anchor and a second anchor, and a tension member connected to the first anchor and the second anchor and sized to span a distance between at least two vertebral bodies. The tension member is designed to allow limited displacement of the first anchor and the second anchor from one another. The system further includes an extension-limiter member connected to the tension member and sized to span the distance between the at least two vertebral bodies. The extension-limiter member provides an increasing resistance to limited displacement of the first anchor and the second anchor from one another as the extension-limiter member is extended from a relatively relaxed state to a relatively taut state. 
         [0006]    According to yet a further aspect, the present disclosure is directed to a surgical method that includes implanting a first bone anchor to a first vertebral body. The surgical method further includes securing one end of a connector to the first bone anchor. The connector has a first tension member and a second, different from the first, tension member designed to limit extension of the first tension member. The method further includes implanting a second bone anchor to a second vertebral body spaced from the first vertebral body and securing another end of the connector to the second bone anchor with tension applied to the first tension member and slack in the second tension member. 
         [0007]    These and other aspects, forms, objects, features, and benefits of the present invention will become apparent from the following detailed drawings and descriptions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a pictorial representation of a vertebral column with a vertebral stabilizing system according to one embodiment of the present disclosure. 
           [0009]      FIG. 2  is a perspective view of a connector in a relatively relaxed condition according to one embodiment of the present disclosure. 
           [0010]      FIG. 3  is a side elevation view of the connector of  FIG. 2 . 
           [0011]      FIG. 4  is a side elevation view of a connector according to another embodiment of the present disclosure. 
           [0012]      FIG. 5  is a side elevation view of a connector according to yet another embodiment of the present disclosure. 
           [0013]      FIG. 6  is a side elevation view of a connector according to a further embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The present disclosure relates generally to the field of orthopedic surgery, and more particularly to systems and methods for stabilizing a spinal joint. For the purposes of promoting an understanding of the principles of the invention, reference will now be made to embodiments or examples illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alteration and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the disclosure relates. 
         [0015]    Referring to  FIG. 1 , the numeral  10  refers to a spinal column having a series of vertebral joints  11 , each including an intervertebral disc  12 . One of the vertebral joints  11  will be described further with reference to adjacent vertebrae  14 ,  16 . The vertebra  14  includes transverse processes  22 ,  24 ; a spinous process  26 ; superior articular processes  28 ,  30 ; and inferior articular processes  29 ,  31 . Similarly, the vertebra  16  includes transverse processes  32 ,  34 ; a spinous process  36 ; superior articular processes  38 ,  40 ; and inferior articular processes (not labeled). Although the illustration of  FIG. 1  generally depicts the vertebral joint  11  as a lumbar vertebral joint, it is understood that the devices, systems, and methods of this disclosure may also be applied to all regions of the vertebral column, including the cervical and thoracic regions. Furthermore, the devices, systems, and methods of this disclosure may be used in non-spinal orthopedic applications. 
         [0016]    A facet joint  42  is formed, in part, by the adjacent articular processes  31 ,  38 . Likewise, another facet joint  44  is formed, in part, by the adjacent articular processes  29 ,  40 . Facet joints also may be referred to as zygapophyseal joints. A healthy facet joint includes a facet capsule extending between the adjacent articular processes. The facet capsule comprises cartilage and synovial fluid to permit the articulating surfaces of the articular processes to remain lubricated and glide over one another. The type of motion permitted by the facet joints is dependent on the region of the vertebral column. For example, in a healthy lumbar region, the facet joints limit rotational motion but permit greater freedom for flexion, extension, and lateral bending motions. By contrast, in a healthy cervical region of the vertebral column, the facet joints permit rotational motion as well as flexion, extension, and lateral bending motions. As the facet joint deteriorates, the facet capsule may become compressed and worn, losing its ability to provide a smooth, lubricated interface between the articular surfaces of the articular processes. This may cause pain and limit motion at the affected joint. Facet joint deterioration may also cause inflammation and enlargement of the facet joint which may, in turn, contribute to spinal stenosis. Removal of an afflicted articular process may result in abnormal motions and loading on the remaining components of the joint. The embodiments described below may be used to stabilize a deteriorated facet joint while still allowing some level of natural motion. 
         [0017]    Injury, disease, and deterioration of the intervertebral disc  12  may also cause pain and limit motion. In a healthy intervertebral joint, the intervertebral disc permits rotation, lateral bending, flexion, and extension motions. As the intervertebral joint deteriorates, the intervertebral disc may become compressed, displaced, or herniated, resulting in excess pressure in other areas of the spine, particularly the posterior bony elements of the afflicted vertebrae. This deterioration may lead to spinal stenosis. In one application, the embodiments described below may restore more natural spacing to the posterior bony elements of the vertebrae, decompress an intervertebral disc, and/or may relieve spinal stenosis. Referring still to  FIG. 1 , in one embodiment, a vertebral stabilizing system  50  may be used to provide support to the vertebrae  14 ,  16 , at least partially decompress the disc  12  and the facet joint  44 , and/or relieve stenosis. 
         [0018]    Connected at each end to vertebral fasteners  53 ( a ),  53 ( b ), a flexible connector  52 , such as a spring rod, may provide compressive support and load distribution, and thereby providing relief to the intervertebral disc  12 . In addition, the flexible connector  52  may dampen the forces on the intervertebral disc  12  and facet joint  44  during motion such as flexion. Because the flexible connector  52  is securely connected to the vertebral fasteners  53 ( a ),  53 ( b ), the flexible connector  52  also provides relief in tension. Accordingly, during bending or in extension, the flexible connector  52  may assist in providing a flexible dampening force to limit the chance of overcompression or overextension when muscles are weak. In addition, the flexible connector  52  allows at least some torsional movement of the vertebra  14  relative to the vertebra  16 . In one exemplary embodiment, the fasteners  53 ( a ),  53 ( b ) include a pedicle screw  55 ,  57  that together with anchors  59 ,  61  secure the flexible connector  52  in place. Such an exemplary fastener is described in U.S. Patent App. Pub. No. 2005/0277922, the disclosure of which is incorporated herein by reference. 
         [0019]      FIG. 2  shows an exemplary embodiment of the flexible connector  52  in greater detail. In this embodiment, the flexible connector  52  is shown as including a spring rod; however, it is understood that the other types of rods may be used. 
         [0020]    Connector  52  includes a spring rod  54  having an anteriorly located center of rotation. The spring rod  54  includes a relatively elastic serpentine body  56  centrally positioned between ends  58 ,  60 . In the illustrative embodiment, the ends  58 ,  60  are generally cylindrical, but it is recognized that the ends may have other profiles, such as, polygonal, oval, and flat, for example. As shown in  FIG. 2 , the serpentine body  56  defines a series of curved portions  62  that support compression and extension of the spring rod  54  when appropriately loaded. That is, when the spring rod  54  is placed under tension from spinal extension, for example, ends  58 ,  60  are pulled away from one another by movement of the spine. As a result, the elasticity of the serpentine body  56  allows for elongation of the spring rod  54  to provide spinal support during spinal extension. 
         [0021]    Conventional spring rods, and other connectors, can be susceptible to early fatigue generally associated with over-extension of the connector during spinal extension, flexion, and rotation. In this regard, the present disclosure includes a connector with an over-extension limiter. In one example, the connector is constructed to include relatively inelastic components that effectively provide extension stops on the relatively elastic connector or spring rod. It is understood that “elastic” and “inelastic” are relative terms and the materials used for the inelastic components may have an elasticity albeit reduced relative to the elasticity of the elastic components. It is also contemplated that the a desired elasticity response for the connector  52  may be achieved by utilizing various types of elastic and inelastic materials in a single implementation. That is, the invention is not limited to a connector having a single-type of elastic components and a single type of inelastic components. 
         [0022]    Referring again to  FIG. 2 , the spring rod body  54  is constructed to have a series of anchors  64  that are threaded with a relatively inelastic member  66 , such as a band, tether, cord, wire, and the like. In the embodiment illustrated in  FIG. 2 , the anchors  64  are formed on outer wall of the curved portions  62  of the spring rod body  54 . In one embodiment, the anchors  64  are integral with the spring rod body  62  and are formed during formation of the spring rod body; however, it is contemplated that the anchors may be joined or otherwise coupled to the spring rod body using adhesive or other suitable means. In the illustrated example, the serpentine body  62  has six anchors  64  and four inelastic members  66  with each curved portion having an anchor, but it is recognized that fewer or more inelastic members could be used and that inelastic members may extend beyond an adjacent curved portion. 
         [0023]    Referring now to  FIG. 3 , a side elevation view of the connector illustrated in  FIG. 2  is shown. The inelastic members  66  traverse a single curved portion  62 . That is, each curved portion  62  is defined by a pair of legs  68 ,  70  that are connected to one another by a curved face  72 . In the illustrated example, each anchor  64  includes an anchor body  74  extending from face  72 . The anchor body  74  further has an opening  76  extending therethrough for passage of an inelastic member. As noted above, the anchor bodies  74  may be integrally formed with or otherwise affixed to faces  72 . 
         [0024]    The inelastic members  66 , which may take the form of tethers, bands, cords, wire, and the like, are looped between adjacent anchors. Thus, in the illustrated example, the centrally located anchors each have two inelastic members whereas the outer anchors have only a single inelastic member. The inelastic members are designed to support the spring rod when the spring rod is under tension. As such, the inelastic members have a slight extendibility to support extension of the spring rod body, but as the spring rod body is extended, the extendibility of the inelastic members is consumed and the inelasticity prevents further extension. In this regard, the inelastic members are preferably installed in a relaxed state and when taut, prevent over-extension of the spring rod body. 
         [0025]    The extendibility of the inelastic members can be defined by their composition, installation with slack, or both. It is contemplated that the inelastic members may have a fibered construction such that the fibers are arranged to provide a certain degree of elasticity. That is, the inelastic members can be constructed such that the fibers are unaligned when in a relaxed state and thus will allow uninhibited extension of the spring rod body until the fibers begin to align with one another. As the fibers begin to align with another, the inelastic member begins to fight further extension of the spring rod body. As the spring rod body is extended by virtue of spinal extension, flexion, or rotation, the inelastic members provide an increasing resistance to such extension. In one example, the inelasticity of the inelastic members is such that full extension of the spring body is prevented. 
         [0026]    In another example, the inelastic members are installed with slack. As such, the inelastic members are installed such that the length of the inelastic members is greater than the distance between adjacent anchors when the spring rod body is in a relaxed state. Thus, as the spring rod body is extended, the distance between anchors increases which results in the slack in the inelastic members being consumed. When the slack is fully consumed, the inelasticity of the inelastic members resists further extension of the spring rod body, i.e., further displacement of the anchors from one another. Accordingly, the amount of slack present in the inelastic member defines the distance the spring rod body will be allowed to extend before the bias of the inelastic members is placed on the spring rod body. Furthermore, unlike the embodiment described in the preceding paragraph, the resistance does not increase as the spring rod body is extended. In other words, the inelastic members do not place a resistance on extension of the spring rod body until the slack is consumed. 
         [0027]    It is also contemplated that the inelastic members can be designed to have a fibered or similar construction that resists extension of the spring rod body as the fibers become more aligned, but be installed so that a slack is present between adjacent anchors. In this embodiment, the spring rod body is permitted to extend as the slack of the inelastic members is consumed. Once that slack is consumed, the inelastic members begin to resist further extension of the spring rod body. That resistance increases as the spring rod is further extended until the fibers in the inelastic members are aligned and the bias of inelastic members is greater than the load imposed by the spinal movement, at which the spring rod body is prevented from further extension. 
         [0028]      FIGS. 4-6  show connectors according to additional embodiments of the present disclosure. The illustrated embodiments are examples of connectors constructed according to the present disclosure; however, the present disclosure is not limited to the illustrated connectors. 
         [0029]      FIG. 4  shows a connector  52 ( a ) wherein openings  78  are formed in the legs  68 ( a ),  70 ( a ) of the curved portions  62 ( a ). The openings  78  are linearly aligned with another and in-line with ends  58 ( a ),  60 ( a ). An inelastic member  66 ( a ) extends through the openings  78  and into ends  58 ( a ),  60 ( a ). In the illustrated example, a locking screw  80  and nut  82  are used to fasten the inelastic member  66 ( a ) to the spring rod  54 ( a ). In one example, bores  84  are defined at each end  86 ,  88  of the inelastic member  66 ( a ) that receive the shaft of locking pin  80 . It is recognized that other attachment devices and techniques may be used to couple the inelastic member to the spring rod. For example, the inelastic member may be adhesively secured to the cylindrical ends. Construction and operation of the inelastic member  66 ( a ) is similar to that described above; however, in this example, only a single inelastic member is shown. But, it is contemplated that multiple inelastic members may be used and those multiple inelastic members may extend through a common set of openings or have respective sets of openings formed in the serpentine body  56 ( a ). 
         [0030]      FIG. 5  illustrates another connector  52 ( b ) according to another embodiment of the present disclosure. In this embodiment, a series of openings  78 ( a ) are formed in the serpentine body and are aligned with one another to define a diagonal channel through the serpentine body. An inelastic member  66 ( b ) is disposed through the diagonal channel and is secured to the serpentine body by anchors  64 ( a ). As the openings through the serpentine body form a diagonal channel, the anchors are on opposing surfaces of the spring rod  54 ( b ). 
         [0031]      FIG. 6  illustrates yet another connector according to another embodiment of the present disclosure. Similar to the connector shown in  FIGS. 2-3 , the connector  52 ( c ) has multiple inelastic members  66 ( c ),  66 ( d ) extending along a periphery of the serpentine body  56 ( c ) of the spring rod  54 ( c ). However, the anchors  64 ( b ) are formed on the cylindrical ends  58 ( c ),  60 ( c ) rather than the curved portions  62 ( c ) of the serpentine body  56 ( c ). With this construction, as the spring rod  54 ( c ) is extended, the serpentine body  56 ( c ) lengthens and the height of the curved portions  62 ( c ) decreases. As the spring rod  54 ( c ) is stretched, the anchors  64 ( b ) are moved farther away from one another which causes slack in the inelastic members  66 ( c ),  66 ( d ) to be consumed. That is, when the spring rod  54 ( c ) is at rest, the curved portions  62 ( c ) of the serpentine body  56 ( c ) are formed to have a height that extends into a path defined along the shortest distance between the anchors  64 ( b ). Thus, to connect to the anchors  64 ( b ), the length of inelastic members  66 ( c ),  66 ( d ) is greater than the distance between the anchors  64 ( b ). This creates some slack in the inelastic members  66 ( c ),  66 ( d ). As the height of the curved portions  62 ( c ) is decreased as a result of extension of the spring rod  54 ( c ), the slack is consumed. Accordingly, the inelastic members  66 ( c ),  66 ( d ) do not resist extension of the spring rod  54 ( c ) until the slack is consumed. 
         [0032]    In one embodiment, the connector  52 ( c ) includes a valley or channel (not shown) formed in the sidewalls of the of the serpentine body  56 ( c ). The channels provide a track in which the inelastic members  66 ( c ),  66 ( d ) fit, and thus slide as the serpentine body is extended and contracted. In this regard, the inelastic members  66 ( c ),  66 ( d ) are prevented from sliding off the serpentine body. Alternately, eyelets or other similar structures (not shown) could be formed with or otherwise attached to the serpentine body to provide a closed track in which the inelastic members  66 ( c ),  66 ( d ) can be retained. 
       The Channels 
       [0033]    The flexible connectors  52  described herein may be placed directly adjacent the vertebrae  14 ,  16 , or alternatively, may be spaced from the vertebrae  14 ,  16 . In some embodiments, placement of the flexible connector  52  directly adjacent the vertebrae  14 ,  16  may impart specific characteristics to the flexible connector  52 . In some examples, the flexible connector  52  may be spaced from the vertebrae  14 ,  16 . Accordingly even when the vertebral column is in flexion, causing the spine to bend forward, the first and second vertebral fasteners  54 ,  56  maintain a line of sight position, so that the flexible connector  52  extends only along a single axis, without bending. In other examples, after placement, the flexible connector  52  may contact portions of the vertebrae  14 ,  16  during the flexion process. For example, during flexion, the vertebrae  14 ,  16  may move so that the first and second vertebral fasteners  54 ,  56  do not have a line of sight position. Accordingly, the flexible connector  52  may be forced to bend around a protruding portion of the vertebrae. This may impart additional characteristics to the flexible connector  52 . For example, because the flexible connector  52  would effectively contact the spinal column at three locations (its two ends  58 ,  60  and somewhere between the two ends), its resistance to extension might be increased. 
         [0034]    In the exemplary embodiments described, the flexible connector  52  is the only component extending from one vertebral fastener  54 ,  56  to the other. This may be referred to as a single flexible connector. This single flexible connector may be contrasted with conventional systems that employ more than one connector extending between attachment points, such as systems with one component connected at the attachment points and another component extending between attachment points. Because it employs a single flexible connector  52 , the vertebral stabilizing system  50  disclosed herein may be easier and quicker to install, may be less complex, and may be more reliable than prior devices. 
         [0035]    It should be noted however, that a spinal column may employ the flexible connector  50  to extend across a first vertebral space, with a second flexible connector extending across a second vertebral space. Accordingly, more than one vertebral stabilizing system  50  may be used in a spinal column. In some instances where more than one stabilizing system is use, the first and second vertebral spaces may be adjacent. In alternative embodiments, a vertebral stabilizing system  50  may have a single flexible connector with a length allowing it to extend across more than one intervertebral space, with or without connecting to an intermediate vertebra. 
         [0036]    In certain anatomies, the vertebral stabilizing system  50  may be used alone to provide decompression or compression to a single targeted facet joint or to relieve pressure on a particular side of the intervertebral disc, such as a herniation area. However, in some instances, a second vertebral stabilizing system may be installed on the opposite lateral side of the vertebrae  14 ,  16 , across from the vertebral stabilizing system  50 . Use of first and second vertebral stabilizing systems may provide more balanced support and equalized stabilization. The second vertebral stabilizing system may be substantially similar to system  50  and therefore will not be described in detail. 
         [0037]    The vertebral stabilizing system  50 , as installed, may flexibly restrict over-compression of the vertebrae  14 ,  16 , thereby relieving pressure on the intervertebral disc  12  and the facet joint  44 . In addition, the vertebral stabilizing system  50  may flexibly restrict axial over-extension of the intervertebral disc  12  and the facet joint  44 . By controlling both compression and extension, the vertebral stabilizing system  50  may reduce wear and further degeneration. The flexible connector  52  may also dampen the forces on the intervertebral disc  12  and facet joint  44  during motion such as flexion and extension. Because the flexible connector  52  may be positioned relatively close to the natural axis of flexion, the vertebral stabilizing system  50  may be less likely to induce kyphosis as compared to systems that rely upon inter-spinous process devices to provide compressive and tensile support. Additionally, the system  50  may be installed minimally invasively with less dissection than the inter-spinous process devices of the prior art. Furthermore, an inter-pedicular system can be used on each lateral side of the vertebrae  14 ,  16 , and may provide greater and more balanced stabilization than single inter-spinous process devices. 
         [0038]    It should be noted that in some embodiments, the flexible connector  52  may be configured so that orientation in one direction provides one set of stabilizing properties to the vertebrae, while orienting the flexible connector  52  in the other direction would provide a second set of stabilizing properties. 
         [0039]    As described above, the flexible connector  52  can be made of elastic or semi-elastic materials in parts or in its entirety. Moreover, the serpentine body  56  may likewise be made of elastic or semi-elastic materials, and further include inelastic components. Exemplary elastic materials include polyurethane, silicone, silicone-polyurethane, polyolefin rubbers, hydrogels, and the like. The elastic materials can be resorbable, semi-resorbable, or non-resorbable. Exemplary inelastic materials include polymers, such as polyetheretherketone (PEEK), polyetherketoneketone (PEKK), and polylactic acid materials (PLA and PLDLA), metals, such as titanium, NITINOL, and stainless steel, and/or ceramics, such as calcium phosphate and alumina. Further, the various connector components can be solid, hollow, semi-hollow, braided, woven, mesh, porous, or combinations thereof. The connector can also be reinforced or semi-reinforced. 
         [0040]    Although disclosed as being used at the posterior areas of the spine, the flexible connector may also be used in the anterior region of the spine to support the anterior column. In such a use, the flexible connector may be oriented adjacent to and connect to the anterior column, and may span a vertebral disc space. 
         [0041]    The foregoing embodiments of the stabilization system may be provided individually or in a kit providing a variety of sizes of components as well as a variety of strengths for the connector. It is also contemplated that the connector&#39;s characteristics may be color coded or otherwise indicated on the connector itself to expedite identification of a desired connector. 
         [0042]    The invention is also embodied in a surgical method for spinal or other bone stabilization. In accordance with this method, a surgeon performs a conventional interbody fusion/nucleus replacement/disc replacement followed by placement of pedicles/bone screws or other inserters into appropriate vertebral or other bony structures. The surgeon may then anchor one end of a connector into a first vertebral or other bony structure. If necessary or otherwise desired, tension is applied to the connector spanning the space between bony structures. Preferably, tension is applied in a limited manner so that inelastic components of the connector are imposing little or no resistance on the applied tension. The un-anchored end of the connector is then anchored to a second vertebral or other bony structure spaced from the first vertebral or other bony structure. Any excess connector extending past the inserters is preferably cut and removed. 
         [0043]    Although only a few exemplary embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this disclosure. Accordingly, all such modifications and alternative are intended to be included within the scope of the invention as defined in the following claims. Those skilled in the art should also realize that such modifications and equivalent constructions or methods do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. It is understood that all spatial references, such as “horizontal,” “vertical,” “top,” “upper,” “lower,” “bottom,” “left,” “right,” “cephalad,” “caudal,” “upper,” and “lower,” are for illustrative purposes only and can be varied within the scope of the disclosure. Further, the embodiments of the present disclosure may be adapted to work singly or in combination over multiple spinal levels and vertebral motion segments. Also, though the embodiments have been described with respect to the spine and, more particularly, to vertebral motion segments, the present disclosure has similar application to other motion segments and parts of the body. In the claims, means-plus-function clauses are intended to cover the elements described herein as performing the recited function and not only structural equivalents, but also equivalent elements.