Patent Publication Number: US-2007106386-A1

Title: Check reins for artificial disc replacements

Description:
REFERENCE TO RELATED APPLICATION  
      This application claims priority from U.S. Provisional Patent Application Ser. No. 60/375,286, filed Apr. 24, 2002, and is a continuation-in-part of U.S. patent application entitled “Methods And Apparatus For Placing Intradiscal Devices,” filed Apr. 23, 2003. The entire content of each application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION  
      This invention relates generally to artificial disc replacements (ADRs) and, more particularly, to check reins for ADRs.  
     BACKGROUND OF THE INVENTION  
      Replacement of cervical discs with synthetic devices that preserve motion could destabilize the cervical spine. Trauma to a destabilized cervical spine could cause spine cord injury. Insertion of most types of artificial disc replacements (ADR) requires cutting the anterior longitudinal ligament and removal of a portion of the anterior half of the annulus fibrosis and nucleus pulposus. Weakening the supporting structures on the anterior portion of the spine increases the probability of spinal cord injury with excessive force from a posterior direction. For example, a patient with an ADR in the cervical spine could become paralyzed from “whiplash” resulting from a motor vehicle accident, Inventions do exist to help prevent the extrusion of ADR materials. For example, U.S. Pat. No. 6,063,121 teaches the use of x-shaped wires about the entire perimeter of the upper and lower plates. Lastly, &#39;121 teaches the use of “wires” in a repeating X pattern. Our preferred embodiment of the device should include other, more flexible materials. Check reins made of inelastic, materials that do not flex well, will limit ADR motion excessively. Circumferential check reins must become lax, allowing the ADR Endplates to approach one another, to permit ADR motion. Repeated bending of wires risks injury to the surrounding tissues. First, the bend in stiff wires could impinge the surrounding tissues. Second, the tissues could be pierced by the ends of broken wires.  
      Similarly, U.S. Pat. No. 3,867,728 teaches the use of Dacron stitching in an X pattern about the periphery of ADRs. U.S. Pat. Nos. 4,911,718; 5,171,281; and 5,545,229 show the use of outer elastic membranes that are reinforced with fibers. The membranes are placed such that the reinforcement fibers are oriented in a crossing pattern between membranes.  
     SUMMARY OF THE INVENTION  
      This invention is broadly directed to check reins in the form of elongated members used to limit the extreme range of motion which would otherwise be permitted by some ADR designs. The check reins serve two main purposes. First, they retain disc spacers, if present. Additionally, the wedge shape of ADRs and the removal of the Anterior Longitudinal Ligament (ALL) and a portion of the Annulus Fibrosus (AF) to insert the ADR from an anterior approach, favor anterior extrusion of disc spacers. In preferred embodiments the check reins are therefore limited to the anterior portion of the periphery of the ADR. Second, check reins serve to prevent excessive spinal motion, Again, although they may be helpful in other locations, anterior check reins help restore the motion limiting functions of the ALL and AF that were removed in anterior approaches to the spine. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  illustrates the use of check reins that are limited to one side of an artificial disc replacement (ADR);  
       FIG. 2  illustrates the use of crossed check reins according to the invention;  
       FIG. 3  is a view of the anterior aspect of an ADR and an alternative embodiment of the invention;  
       FIG. 4A  is a view of the anterior aspect of an ADR and an alternative embodiment of the device;  
       FIG. 4B  is an exploded view of the lateral aspect of the ADR shown in  FIG. 4A ;  
       FIG. 4C  is a view of the anterior aspect of an ADR and the embodiment of the ADR shown in  FIG. 4B ; and  
       FIG. 5  is an axial cross section of the ADR of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The invention is broadly directed to check reins in the form of elongated members used to limit the extreme range of motion which would otherwise be permitted by some ADR designs. The check reins serve two main purposes. First, they retain disc spacers, if present. Additionally, the wedge shape of ADRs and the removal of the Anterior Longitudinal Ligament (ALL) and a portion of the Annulus Fibrosus (AF) to insert the ADR from an anterior approach, favor anterior extrusion of disc spacers. In preferred embodiments the check reins are therefore limited to the anterior portion of the periphery of the ADR.  
      Second, check reins serve to prevent excessive spinal motion. Again, although they may be helpful in other locations, anterior check reins help restore the motion limiting functions of the ALL and AF that were removed in anterior approaches to the spine. As illustrated in  FIG. 2A , check reins may helpful in the anterior and posterior portions of ADRs. Check reins may also be used about all sides of the ADR. Note that it is not necessary according to the invention to have closely approximated check reins about the periphery of the ADR. Spaces between groups of check reins about the periphery of the ADR may allow ADRs to move better, as shown in  FIG. 5 .  
      Furthermore, in contrast to existing devices, elastic and more flexible or resilient designs are used in accordance with this invention. Braided materials, for example, are more flexible and have improved longevity. The braided materials could include wire filaments (cable), polymer filaments, or filaments of other biologically acceptable material. My co-pending U.S. patent application entitled “Methods And Apparatus For Placing Intradiscal Devices” teaches the use of biologic materials that may be used to form check reins according to this application. According to this embodiment, ligaments and/or bone are grafted from one vertebra to another vertebra. The reconstructed or augmented AF and ALL also help retain intradiscal devices and prevent excessive vertebral motion.  
      Turning now to the drawings,  FIG. 1  is a side-view drawing showing the use of an anterior check rein to prevent extension, for example. Lateral check reins may be used to prevent lateral bending, and cross-coupled check reins may be used to prevent translation.  FIG. 2  depicts the use of cross-coupled check reins.  
       FIG. 3  is a view of the anterior aspect of an ADR and an alternative embodiment of the invention. Multiple crossed check reins are illustrated on the anterior aspect of the ADR.  FIG. 4A  is a view of the anterior aspect of an ADR and an alternative embodiment of the device. Multiple check reins are illustrated. Some of the check reins cross. The check reins can be assembled and tightened in-situ.  
       FIG. 4B  is an exploded view of the lateral aspect of the ADR drawn in  FIG. 4A . A disc spacer is seen anterior to the ADR endplates. Some of the check reins have been connected to both of the ADR EPs. Other check reins are connected to only the bottom ADR EP. The loose check reins will be threaded to the upper ADR EP after the disc spacer is inserted. In-situ assembly of the check reins eases insertion of the disc spacer. In-situ assembly also allows surgeons to select the optimal tension on the check reins.  
       FIG. 4C  is a view of the anterior aspect of an ADR and the embodiment of the ADR drawn in  FIG. 4B . The disc spacer has been inserted between the ADR EPs. Two of the check reins are shown threaded through both ADR EPs. The check reins can be tightened and locked into position by crimping components that slide over the check reins. The excess check rein can be cut and removed after the final tightening of the check reins.  
       FIG. 5  is an axial cross section of an ADR. The dotted areas of the drawing represent potential locations for check reins in one embodiment of the device. Gaps between groups of check reins facilitate ADR motion. Other embodiment of the device may group check reins in other location about the periphery of the ADR.