Dynamic spinal stabilization assembly with elastic bumpers and locking limited travel closure mechanisms

Abstract

A dynamic stabilization assembly includes a core, typically in the form of a tensioned cord, at least one pair of bone anchors, a spacer surrounding the core located between the bone anchors, at least one elastic bumper and at least one fixing or blocking member. The core is slidable with respect to at least one of the bone anchors, the spacer and the bumper. The bumper is compressed. Bone screws of the assembly include closure structures that lock against the bone screw independent of any fixing or sliding of the core with respect to the bone screw.

What is claimed and desired to be secured by Letters Patent is as follows: 
     
         1 . In a medical implant assembly having at least first and second bone anchors and a longitudinal connecting member, the connecting member having a core and a spacer, the spacer surrounding the core and located between the first and second bone anchors, the core extending through and directly engaging each of the first and second bone anchors, the improvement comprising:
 a) at least a first closure mechanism in fixed locking engagement with the first bone anchor, the first closure mechanism capturing the core within the bone anchor, the first closure mechanism having at least a bottom surface spaced from a surface of the first bone anchor providing clearance between the first closure mechanism and the bone anchor for sliding movement of the core with respect to the bone anchor when the first closure mechanism is locked to the first bone anchor;   b) at least one compressible elastic bumper having a through bore, the core disposed in the bore and slidable with respect to the bumper, the bumper disposed adjacent the first bone anchor and opposite the spacer; and   c) a fixing member, the elastic bumper disposed between the first bone anchor and the fixing member, the fixing member frictionally engaged with the core and in compressible engagement with the elastic bumper.   
     
     
         2 . The improvement of  claim 1  wherein the core is a tensioned cord. 
     
     
         3 . The improvement of  claim 1  wherein the fixing member is a crimping ring surrounding the core and pressing there against. 
     
     
         4 . The improvement of  claim 1  wherein the fixing member abuts directly against the elastic bumper. 
     
     
         5 . The improvement of  claim 1  wherein the spacer is compressible. 
     
     
         6 . The improvement of  claim 1  further comprising a second closure mechanism in locking engagement with the second bone anchor, the second closure mechanism having a lower portion, the lower portion pressing against the core and locking the core against an inner surface of the second bone anchor. 
     
     
         7 . The improvement of  claim 6  wherein each of the bone anchors have an inner guide and advancement structure with a run-out seat that engages a portion of the first or second closure top mechanism to fix the closure top to the bone screw independent of fixing the core to the bone anchor. 
     
     
         8 . In a medical implant assembly having at least first and second bone anchors with an elongate cord under tension disposed between the first and second bone anchors, and a spacer surrounding the cord, the spacer located between the first and second bone anchors, the improvement comprising:
 a) a compressed elastic bumper in slidable engagement with the cord and disposed adjacent the second bone anchor and opposite the spacer; and   b) a fixing structure pressing against the elastic bumper and fixed to the cord, the cord being held in tension between the fixing structure and the first bone anchor, the cord being fixed against the first bone anchor and in slidable engagement with the second bone anchor.   
     
     
         9 . The improvement of  claim 8  wherein the fixing structure is a crimping ring surrounding the cord and pressing there against. 
     
     
         10 . The improvement of  claim 8  wherein the spacer is compressible. 
     
     
         11 . A method of fastening a dynamic stabilization connecting member to at least first and second bone anchors comprising:
 a) fixing the first bone anchor to an elastic cord having a slidable outer spacer thereon;   b) locating the spacer between the first bone anchor and the second bone anchor;   c) capturing the cord within the second bone anchor with the cord being in slidable relationship with the second bone anchor;   d) threading an elastic bumper on the cord and placing the bumper adjacent the second bone anchor opposite the spacer;   e) threading a fixing structure on the cord and placing the fixing structure adjacent the elastic bumper;   f) tensioning the cord; and   g) pressing the fixing structure against the elastic bumper to compress the bumper and frictionally engaging the fixing structure to the tensioned cord.