Abstract:
An implantable device for stabilizing at least a portion of a spinal column. The implantable device comprises an implantable artificial facet joint and one or more artificial ligaments connecting the implanted artificial facet joint to a third vertebra disposed adjacent to either the first or the second vertebra. The artificial facet joint, when implanted, spans a first vertebra and a second vertebra, adjacent to the first vertebra.

Description:
BACKGROUND OF THE INVENTION 
     The vertebrae in a patient&#39;s spinal column are linked to one another by the disc and the facet joints, which control movement of the vertebrae relative to one another. Each vertebra has a pair of articulating surfaces located on the left side, and a pair of articulating surfaces located on the right side, and each pair includes a superior articular surface, which faces upward, and an inferior articular surface, which faces downward. Together the superior and inferior articular surfaces of adjacent vertebra form a facet joint. Each joint is surrounded by a capsule of connective tissue and produces a fluid to nourish and lubricate the joint. The joint surfaces are coated with cartilage allowing the joints to move or articulate relative to one another. 
     Diseased, degenerated, or otherwise impaired facet joints and/or discs can be surgically removed and prosthetic discs and/or facet joints implanted to restore natural function of a spine. Similar surgery may also be required after a laminectomy (removal of lamina), since a laminectomy predisposes the patient to instability and may lead to post-laminectomy kyphosis (abnormal forward curvature of the spine), pain, and neurological dysfunction. 
     However, implantation of an artificial facet joint frequently requires removal of a significant portion of the posterior ligamentous structures of the spine. This results in incomplete restoration of natural function of a spine as well as decreased stability and increased mobility (increased range of motion) of the patient&#39;s spinal column. Accordingly, there is a need for an artificial facet joint that would restore the natural function of a spine, including that of posterior ligaments. 
     SUMMARY OF THE INVENTION 
     The present invention is an implantable device, kit, and related methods for replacing or augmenting facet joints and spinal ligamentous structures. The device of the present invention includes an artificial facet joint that restore the function of diseased, degenerated, or otherwise impaired facet joint. The device also includes artificial ligaments that restore the functions of spinal ligamentous structures resected during the implantation of the artificial facet joint. Particularly, when implantation of artificial facet joint requires the removal of spinous process or the removal of both lamina and spinous process, the ligamentous structures that attach to the spinous process and lamina are also resected. Therefore, device of the present invention includes artificial ligaments to restore functions of any spinal ligaments removed during the implantation of the artificial facet joint. 
     In one embodiment, the present invention is an implantable device for stabilizing at least a portion of a spinal column. The implantable device comprises one or more implantable artificial facet joints and one or more artificial ligaments. The artificial facet joint replaces or augments the function of the diseased facet joint or joints, and when implanted, it spans a first vertebra and a second vertebra adjacent to the first vertebra. The artificial ligaments replace any spinal ligaments resected during the implantation of the artificial facet. The artificial ligaments span between the first and second vertebrae coupled by the facet joint, and the artificial ligaments span between a third vertebra and either of the first or the second vertebra coupled by the facet joint. The ends of an artificial ligament can couple to the vertebra, or the ends may couple to the facet joint replacement. 
     In another embodiment, the present invention is a kit for restoring the function of a spinal segment. The kit comprises components to assemble at least one artificial facet joint and at least one artificial ligament. The artificial facet joint, when implanted, spans a first vertebra, and a second vertebra adjacent to the first vertebra. The artificial ligament spans the first and second vertebrae coupled by the artificial facet joint. Additionally or alternatively, the artificial ligament span a third vertebra and either of the first or the second vertebra coupled by the artificial facet joint. The kit may also include multiple sizes and orientations of artificial facet joints and artificial ligaments to accommodate various patient anatomies and sizes. 
     In another embodiment, the present invention is a method of restoring the function of a spinal segment. The method comprises the step of connecting at least one artificial ligament between a third vertebra and either of the first or a second vertebra coupled by the artificial facet joint. Alternatively, the method comprises the step of connecting at least one artificial ligament between an artificial facet joint, said artificial joint spanning a first and a second adjacent vertebrae, and a third vertebra disposed adjacent to the first or the second vertebra. 
     A device, a kit and a method of the present invention advantageously restores natural mobility and stiffness of a spinal segment by introducing an artificial facet joint and ligament device that restores connection between two adjacent vertebrae coupled by facet joints and connection between a third vertebra and either of the two vertebrae coupled by the artificial facet joint. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-section of a representative vertebra. 
         FIG. 2A  is a side view of a functional spinal unit (FSU). 
         FIG. 2B  is a posterior view, respectively, of a functional spinal unit (FSU). 
         FIG. 3  is a side view of portion of a spinal column that includes three sequential vertebrae. 
         FIGS. 4A and 4B  are a side view and a posterior view, respectively, of three sequential vertebrae following a facetectomy (removal of facet joints) and laminectomy (removal of lamina and spinous process). 
         FIG. 5  depicts one embodiment of a device of the present invention. 
         FIG. 6  depicts one embodiment of a device of the present invention. 
         FIG. 7  depicts an alternative embodiment of a device of the present invention. 
         FIGS. 8A through 8E  depict alternative embodiments of the attachment means that can be employed as components of the device of the present invention to vertebrae. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
     Referring to  FIG. 1 , a cross-section of a representative vertebra is shown. Vertebra  100  includes vertebra body  102 , spinal canal  104 , pedicle  106 , lamina  108 , spinous process  110  and transverse processes  112 . 
       FIGS. 2A and 2B  depict a side view and a posterior view, respectively, of a functional spinal unit (FSU). An FSU comprises inferior vertebra  202  and superior vertebra  204  connected by intervertebral disk  206 , facet joints  208 (located inside the facet joint capsule), and all ligaments (not shown) connecting inferior vertebra  202  and superior vertebra  204 . Vertebrae  202  and  204  include posterior-facing spinous processes  210  and laterally facing transverse processes  212 . 
     Referring to  FIG. 3 , vertebra  320 , superior and adjacent to vertebra  304 , is shown. In addition to intervertebral disks  306  and facet joints  308  (located inside the facet joint capsule and capsulary ligament  332 ), various ligaments provide further support to a spinal column. Of all spinal ligaments, the particular ligaments of related to this invention are ligamentum flavum (not shown), interspinous ligament (not shown), supraspinous ligament  330 , and facet capsulary ligament  332 . 
       FIGS. 4A and 4B  depict lateral and posterior views, respectively, of three sequential vertebrae following a facetectomy (removal of facet joints  408 ) between vertebrae  402  and  404  and laminectomy (removal of lamina and spinous process) on vertebra  404 . As can be seen, vertebra  404  lacks spinous process  410 . Vertebrae  402  and  404  are no longer coupled by facet joints  408 . Facet joints  408  are intact between vertebra  404  and  420 . With reference to  FIGS. 4A and 4B , and by comparison to  FIG. 3 , vertebrae  402  and  404  are no longer connected, such as are  404  and  420 , by capsulary ligaments  432 , interspinous ligament  422 , and supraspinous ligament  430 . Also, vertebrae  404  and  420  are no longer connected by an interspinous ligament and a supraspinous ligament. 
       FIG. 5  depicts one embodiment of a device of the present invention. Similar to  FIG. 4B , three sequential vertebrae,  502 ,  504  and  520 , are shown in a patient following a facetectomy between vertebrae  502  and  504  and laminectomy on vertebra  504 . The device of the present invention comprises artificial facet joint  550 . Artificial facet joint  550  has been implanted between vertebrae  502  and  504 . The device of the present invention further includes artificial ligaments  590 . 
     Artificial facet joint  550  represents a generic artificial facet joint that require removal of at least a portion spinous process  510  of vertebra  504  as represented by “X”. In the embodiment shown in  FIG. 5 , the entire spinous process of  510  of vertebra  504  is removed by laminectomy and facetectomy. Artificial facet joint  550  restore the function of resected anatomy between vertebrae  502  and  504 , including facet joints  508 , capsulary ligaments, interspinous ligament, and supraspinous ligament. However, resection of spinous process  510  of vertebra  504  also removes at a portion of ligamentous connection between vertebrae  504  and  520 , including interspinous ligament and supraspinous ligament between vertebrae  504  and  520 . Therefore, artificial ligament  590  restores the function of the resected ligaments between vertebrae  504  and  520 . 
     In one embodiment, artificial facet joint  550  includes coupling member  552 . Referring to the embodiment shown in  FIG. 5 , artificial facet joint  550  includes connectors  554  and  556 . Connector  554  connects coupling member  552  to vertebra  502  using pedicle screws  558 . Connector  556  connects coupling member  552  to vertebra  504  using pedicle screws  560 . 
     In the embodiment shown in  FIG. 5 , vertebra  520  is disposed adjacent and superior to vertebra  504 , following facetectomy and laminectomy. Artificial ligaments  590  connect vertebrae  504  and  520 . In one embodiment, artificial ligaments  590  are attached to vertebra  520  by pedicle screws  592 . The other ends of the artificial ligaments  590  are attached by pedicle screws  560  that are the same pedicle screws used to attach artificial facet joints  550 . Although pedicle screws  592  are used to attach artificial ligaments  590  to vertebra  520 , artificial ligaments  590  may attach to other bony anatomy on vertebra  520  directly or indirectly using another mechanism. As non-limiting examples, artificial ligaments  590  can attach to vertebra  520  at vertebral body, pedicle, lamina, spinous process, transverse process, superior articular process, or inferior articular process. Moreover, artificial ligaments  590  mat not attach directly on vertebra  520 , but it may wrap around any bony protrusion in vertebra  520  with or without any aid of another component such as a hook. Various means of attachment are discussed later. The opposite ends artificial ligaments  590  can also attach or wrap to various site on vertebra  504  similar to vertebra  520 . Furthermore, artificial ligaments  590  may attach to vertebra  504  indirectly through the artificial facet joint  550 . Again, as non-limiting examples, same attachment mechanism such as bone screws can be used to attach both artificial facet joint  550  and artificial ligaments  590 , or artificial ligaments  590  may attach to any part of artificial facet join  550 , including the connector  556 . Any of the currently used artificial facet joints can be used as components of the device of the present invention. In one embodiment, an artificial facet joint described in the U.S. Pub. App. No. 2005/0055096 is used. Other embodiments include those described in U.S. Pat. Nos. 6,419,703, 6,565,605, 6,579,319, 6,610,091, 6,669,729, 6,902,580 and U.S. Pub. App. Nos. 2003/0004572, 2003/0028250, 2003/0040797, 2004/0006391, 2004/0049281, 2004/0049278, 2004/0049277, 2004/0049276, 2004/0049275, 2004/0049274, 2004/0049273, 2004/0049272, 2004/0111154, 2004/0254575, 2005/0027361, 2005/0033434, 2005/0085912, 2005/0102028, 2005/0119748. The entire teachings of these patents and published applications are herein incorporated by reference. Other examples of suitable artificial facet joints are described in U.S. Ser. Nos. 10/905,374 and 11/171,022, the teachings of which are incorporated herein in their entirety. 
     Referring to  FIG. 6 , an embodiment of the present invention is shown. Three sequential vertebrae,  602 ,  604  and  620 , are shown in a patient following facetectomy between vertebra  602  and  604  and laminectomy on vertebra  604 . Artificial facet joint  650  has been implanted. Artificial facet joint  650  includes coupling member  652 . Connectors  654  and  656  connect coupling member  652  to vertebrae  602  and  604  using pedicle screws  658  and  660 . Artificial facet joint  650  further includes spinous process support  670 . Spinous process support  670  further contributes to restoration of natural function of the functional spinal units comprising vertebrae  602  and  604  and vertebrae  604  and  620  by supporting spinous process  610  of vertebra  620 . Artificial ligaments  690  are attached to spinous process support  670 . In the embodiment shown in  FIG. 6 , artificial ligaments  690  are attached to spinous process  610  using spinous process hook  692 . Therefore, vertebrae  604  and  620  are connected by the artificial ligaments  690 . 
     Referring to  FIG. 7 , an alternative embodiment of a device of the present invention is shown. Three sequential vertebrae,  702 ,  704  and  720 , are shown in a patient following facetectomy between vertebra  704  and  720  and laminectomy on vertebra  704 . An embodiment of artificial facet joint  750  has been implanted. Artificial facet joint  750  includes coupling member  752 . Connectors  754  and  756  of facet joint  750  connect support member  752  to vertebrae  704  and  720  using pedicle screws  758  and  760 . The device of the present invention further includes artificial ligaments  790  that connect vertebrae  702  and  704 . Artificial ligaments  790  are attached to vertebra  702  by pedicle screws  792 . The other ends of the artificial ligaments  790  are attached by pedicle screws  750  that are the same bone screws used to attach artificial facet joints  750 . In the embodiment shown in  FIG. 7 , vertebra  702  is adjacent and inferior to vertebra  704 , and vertebra  704  has received facetectomy of the superior facet joint, and laminectomy. Further, the embodiment of artificial facet joint  750  of the device shown in  FIG. 7  includes additional artificial ligaments  794  that connects vertebrae  704  and  720 . In this embodiment, artificial ligaments  794  are attached to pedicle screws  758  and  760 . Additional artificial ligaments  794  additionally restores function lost by facetectomy and resection of the posterior spinal ligaments between vertebrae  704  and  720 , including capsulary ligaments interspinous ligaments and supraspinous ligaments. 
       FIGS. 8A through 8E  show additional examples of the attachment means that can be employed to attach artificial ligaments  890  of the device of the present invention to vertebra  820 . The attachment mechanism listed in  FIGS. 8A and 8E  are not exhaustive, and a person skilled in the art will recognize that additional attachment mechanism can be used. Variety of bone screws, hooks, rivets, wires, and cables can be employed to secure the artificial ligaments to the vertebra or wrap the artificial ligaments around the vertebra.  FIG. 8A  shows bone screws  892 , attachable to pedicles.  FIG. 8B  shows bone screw or bone rivet  894 , attachable to spinous process  810 .  FIG. 8C  shows spinous process hook  896 , attachable to spinous process  810 .  FIG. 8D  shows laminar hooks  898 , attachable to lamina  811 .  FIG. 8E  shows transverse process hooks  900  attachable to transverse processes  913 . 
     Coupling member(s) and connectors of an artificial facet joint of the device of the present invention can be rigid or flexible. In one embodiment, the coupling members and the connectors are flexible. In another embodiment, the connectors are substantially rigid rods. Each flexible member can have a variety of configurations, shapes, and sizes. Coupling members can be formed from a wide range of biocompatible materials. Coupling members, in one embodiment, are formed from a polymer, and more preferably a biocompatible polymer, such as polyurethane, composite reinforced polyurethane, silicone, etc. Connecting members can be produced from such materials as metals, ceramics, polymers, etc. 
     Artificial ligaments of a device of the present invention perform a function of any combination of natural interspinous ligament, supraspinous ligament, and facet joint capsulary ligament. Therefore, artificial ligaments should have tensile strength of at least 50 N, preferably 100 N, more preferably 200 N. When extended with 200 N load, the ligament should produce at least 5% strain, preferably 10% strain, more preferably 30% strain. The artificial ligament should limit the flexion of a functional spinal unit to 15 degrees, preferably no more than 12 degrees of flexion. 
     In other embodiment, the flexible members may have no or low strain (less than 5% strain when loaded with 200 N). However, the ligament should be flexible to easily bend. When implanted, the ligament may be slack in the neutral position to allow flexion of a functional spinal unit to at least 6 degrees, preferably at least 12 degrees. 
     The artificial ligaments can be made of any biocompatible material including polyesters, polypropylene, polyethylene, carbon fiber, glass, glass fiber, polyurethane, plyaramide, metals, polymers, copolymers, polyactic acid (PLA), polyglycolic acid (PGA), silk, cellusoseic acid, polycaproactone fibers, or any combination of above. To increase the tensile strength multiple fibers can be weaved to form a band. Furthermore, in some embodiments, the flexible members may have time-dependent behavior such as creep. Thereby, the property of the artificial ligament changes over time. For example, the flexible member may be very stiff (e.g., allowing 5 degrees flexion) initially after implantation to protect the surrounding injured tissues and become more compliant due to creep as time progresses (e.g., allowing 10 degrees flexion after 3 months). 
     Furthermore, the artificial ligaments can be lubricated to lower the friction and wear between its fibers and/or between the ligament and surrounding structures (facet joint, bony structure, other soft tissues) using lubricants including hyaluronic acid, proteoglycans, and hydrogels. Finally, the artificial ligaments can be made of at least in part by subintestinal submucosa (SIS) to assist in the formulation of natural ligamentous tissue. 
     EQUIVALENTS 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.