Abstract:
A method of repairing a bone joint by using a simple and flexible artificial ligament which easily conforms to a patient&#39;s anatomy and can be used independently or in combination with an intervertebral graft, implant or prosthesis to return stability to the spine subsequent to a surgical spine procedure, is disclosed. The method includes anchoring the artificial ligament to at least two vertebrae to aid in restoring stability to the compromised joint. The artificial ligament is also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 09/543,288 filed Apr. 5, 2000 now U.S. Pat. No. 6,585,769 which claims the benefit of U.S. Provisional Patent Application No. 60/127,735, filed Apr. 5, 1999, the entire disclosure of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present disclosure relates generally to prosthetic members for joining or repairing bone segments, including artificial ligaments and, more specifically, to an artificial ligament intended for partial or full replacement of the anterior longitudinal ligament of the anterior lumbar, thoracic or cervical spine. 
     Ligaments extend between adjacent bone structures and serve a primary function of maintaining and providing appropriate stability to the bone structures to maintain the structures in aligned, spaced relation, particularly when subjected to loads in tension or upon torsional movement. Spinal ligaments stabilize and support vertebral bodies during movement of the spine. 
     During surgical treatment of the spine, a section of a spinal ligament may be resected to provide access to a diseased or damaged intervertebral disc and/or to permit introduction of a fusion implant, bone graft or intervertebral disc prosthesis intended for long term support of the vertebral bodies. The bone graft, fusion implant or intervertebral disc return stability to the spinal column in compression and flexing, however, due to removal of the spinal ligament, the biomechanical characteristics of extension and torsional stability lost by the ligament&#39;s removal must be replaced. Current techniques involve the use of metal bone plates which are secured to the vertebral bodies with screw locking mechanisms. Conventional bone plates, however, are rigid and, thus, significantly inhibit spine mobility. Additionally, the screw locking mechanisms utilized with such plates are relatively complicated and provide minimal flexibility with respect to fastener positioning, etc. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present disclosure is directed to a simple and flexible artificial ligament which easily conforms to a patient&#39;s anatomy and can be used independently or in combination with an intervertebral graft, implant or prosthesis. In one preferred embodiment, an artificial spinal ligament is in the form of a flexible conformable plate dimensioned to span adjacent vertebrae and having openings for reception of bone screws, fasteners, etc. to mount the plate to the vertebrae. The biomechanical supporting characteristics of the plate approximate the characteristics of the ligament (e.g., anterior spinal) which it replaces thereby providing appropriate support to the spine in extension which also permitting normal spine mobility. A method of supporting adjacent vertebrae with the artificial ligament is also disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the disclosure are described herein with reference to the drawings wherein: 
         FIG. 1  is a perspective view of the artificial ligament of the present disclosure; 
         FIG. 2  is a top plan view of the artificial ligament of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view taken along lines  3 — 3  of  FIG. 2 ; 
         FIG. 4  is a perspective view of an alternate embodiment illustrating mounting thereof to the vertebral column; 
         FIG. 5  is a top plan view of an alternate embodiment of FIG. I; 
         FIG. 6  is a cross-sectional view taken along lines  6 — 6  of  FIG. 5 ; and 
         FIG. 7  is a perspective view of another alternate embodiment of the artificial ligament. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings, in which like reference numerals identify similar or identical elements throughout the several views, there is illustrated the artificial ligament of the present disclosure. The artificial ligament of the present disclosure is intended to replace part or all of the supporting function of a ligament previously removed in connection with a surgical procedure. The artificial ligament has particular application in replacing the supportive function of a spinal ligament, e.g., anterior or posterior, which may have been fully or partially resected during a spinal procedure. The artificial ligament is advantageously dimensioned to be positioned to span adjacent vertebrae to restore the natural biomechanics, e.g., including tensional support and range of motion, of the removed ligament segment. The artificial ligament is contemplated for use with a bone graft, fusion implant or artificial disc to compliment the compressive load characteristics of the implant with its tensional supporting capabilities during healing. It is also envisioned that the ligament may be utilized in other capacities such as, for example, repair of other body ligaments such as the anterior crucial ligament, etc. 
     Referring initially to  FIGS. 1–3 , artificial ligament  100  includes ligament body or plate  102  which is advantageously dimensioned to span at least two adjacent vertebrae. It is envisioned that the ligament body  102  may span three or more vertebral bodies. In a preferred embodiment, the length “l” of ligament body  102  ranges from about 1–3 inches, preferably about 2 inches. 
     Ligament body  102  is preferably fabricated from a generally flexible material. The selected flexible material of ligament body  102  preferably has physical characteristics which approximate the biomechanical characteristics of the spinal ligament which it replaces. More specifically, the selected material of ligament body  102  supports the spine and provides stability in extension, i.e., the ligament body has tensional load bearing capabilities while also permitting a degree of flexibility approximating the natural ligament. A preferred material of fabrication for ligament body  102  includes a flexible polymeric material such as polyethylene. 
     Ligament body  102  defines first and second web body end portions  104  connected through intermediate body portion  106 . Web body end portions  104  each include a pair of apertures  108  for reception of bone fasteners  110 . As best depicted in  FIG. 2 , apertures  108  may be generally elongated or slotted in the longitudinal direction with respect to longitudinal axis “a” of body  102  to permit multi-position capabilities of the bone fasteners  110  with respect. to ligament body  102  and the vertebral bodies as will be discussed. Apertures  108  are preferably countersunk defining a beveled or chamfered surface  112  adjacent the upper surface of the ligament body  102  for reception of the head  114  of the bone fasteners  110  in flush relation therewith. Although two apertures  108  are shown in each web end portion  104  of the preferred embodiment, it is envisioned that each web portion  104  may have more than two apertures or only one aperture. With particular reference to  FIG. 2 , intermediate body portion  106  has a width “w” which is substantially less than the corresponding width of web portion  104 . Such dimensioning reduces the transverse profile of ligament body  102  thereby increasing flexibility to facilitate torsional movement of ligament body  102  upon corresponding movement of the patient&#39;s spine. The width “w” of intermediate body portion  102  ranges from about 0.125 inches to about 0.375 inches, more preferably, about 0.250 inches. 
     With reference again to  FIG. 1 , bone fasteners  110  serve as anchoring means for securing the ligament body  102  to the adjacent vertebrae. The preferred bone fastener  110  includes a fastener head  114  and a fastener shaft  116  extending from the fastener head. The fastener shaft  116  is threaded preferably with a self-tapping thread  118 . Upon mounting of bone fastener  110  within the adjacent vertebrae, the fastener head  114  is preferably flush with the upper surface of the ligament body  102 . Other anchoring means for mounting ligament body  102  to the vertebral bodies are envisioned by one skilled in the art including expandable bolts, screws, non-threaded fasteners, etc. 
     In use in connection with an anterior spinal procedure, the anterior ligament is removed to permit access to a diseased or damaged disc section. A partial or full discectomy may be performed followed by insertion of a bone graft, fusion implant (e.g., as disclosed in U.S. Pat. No. 4,961,740, the contents of which are incorporated herein by reference) or an intervertebral prosthesis (such as disclosed in commonly assigned application Ser. No. 09/098,606, filed Jun. 17, 1998, the contents of which are incorporated herein by reference). 
     When used with fusion devices, the bone fasteners  110  are placed at the outer area  108   r  of the openings  108  so the ligament is rigid in tension while allowing for compression. This provides for immediate stability in extension as extension loads immediately place the ligament in tension. The fasteners  110  are free to move within openings  108  relative to the ligament  102  in compression. This also permits graft compression. 
     When used with artificial discs, the fasteners  110  are placed in the middle  108   m  or inner part  108   i  of the openings  108  to permit limited relative motion of fasteners  110  within openings  108  of the ligament in both flexion and extension. Extension ultimately leads to tension in the ligament as the fasteners  110  meet the ends  108   r  of the openings  108 . Thus, movement in tension and compression is provided. This flexibility also reduces the likelihood of the fasteners  110  backing out over time. 
       FIG. 4  illustrates an alternate embodiment of the artificial ligament where intermediate body portion  106  includes an elongated longitudinal depression  120  defining a reduced thickness of ligament body  102 . This reduced thickness permits the surgeon to create an additional opening  108  in the ligament body  102  to receive a bone fastener  110  for further fixation to the vertebrae. More specifically, during the surgical procedure the surgeon may create an opening at a desired location within intermediate body portion  106  with a punch or the like. A multitude of openings (shown in phantom) may be formed within depression  120 . This feature facilitates use of ligament body  102  in spanning more than two vertebrae, e.g., three vertebrae.  FIG. 4  illustrates this embodiment mounted to the spinal column and spanning three (3) vertebral portions “v 1 –v 3 ” with the middle opening  108  having a fastener for attachment to the intermediate vertebrae “v 2 ” and the outer openings  108  having fasteners  110  mounted to respective vertebrae “v 1 ” “v 3 ”. Depression  120  preferably also defines a transverse dimension “t” which approximates the diameter of the fastener head  114  to facilitate retention of the head with respect to the ligament body  102 . 
       FIGS. 5 and 6  illustrate an alternate embodiment of the artificial ligament  100  of  FIG. 1 . Artificial ligament  200  is substantially similar to the ligament  100 , but, differs primarily in its dimensioning. More specifically, the length “l” of ligament body  102  is shorter than the length “l” of the embodiment of  FIG. 1 , preferably ranging in length from about 0.75–1.25 inches, more preferably about 1.14 inches. In all other respects, the ligament  200  is identical to ligament  100  Of  FIG. 1 . 
       FIG. 7  illustrates another alternate embodiment of the ligament of the present disclosure. Ligament  300  includes a slight arcuate bend  302  or bump adjacent its intermediate portion. The arcuate bend provides a degree of excess material to permit the effective length of the ligament to increase when ligament  300  is placed in tensioned, i.e., the arcuate bend will tend to straighten under extension. The ligament  300  will become increasingly stiffer with a higher tension load. Multiple bends are also envisioned to establish non-linear stiffness. 
     While the above description contains many specifics, these specifics should not be construed as limitations on the scope of the disclosure, but merely as exemplifications of preferred embodiments thereof. For example, the present prosthetic device disclosed herein may be implanted to repair a variety of bone structures such as the ankle, knee, wrist, etc. Those skilled in the art will envision many other possible variations that are within the scope and spirit of the disclosure.