Methods and apparatus for coupling a prosthesis to a spinal segment

Abstract

A method for coupling a prosthesis to a spinal segment in a patient includes the steps of selecting first and second reference points disposed along the spinal segment and pre-operatively measuring a target distance. The target distance extends between the first and second reference points while the patient is in a preferred posture such as the standing position. A prosthesis is coupled to the spinal segment and the prosthesis is then intra-operatively adjusted in order to set the distance between the first and second reference points based on the target distance.

What is claimed is: 
     
         1 . A system for restricting flexion of a spinal segment in a patient, said system comprising:
 a tether structure comprising one or more straps adapted to be coupled with a superior spinous process and an inferior spinous process or sacrum;   a first compliance element coupled with the tether structure and configured to elastically elongate as tension is applied through the tether structure; and   a first constraining tool releasably coupled with the compliance element so as to hold the compliance element in a first desired position and allow a first predetermined amount of elastic elongation of the first compliance element as tension is applied to the first compliance element though the tether structure.   
     
     
         2 . A system as in  claim 1 , wherein the tether structure is substantially non-distensible. 
     
     
         3 . A system as in  claim 1 , wherein the first constraining tool comprises an elongate shaft. 
     
     
         4 . A system as in  claim 1 , wherein the first constraining tool comprises a cradle adapted to releasably hold the first compliance element. 
     
     
         5 . A system as in  claim 1 , wherein the first constraining tool comprises a plurality of elongate arms, the plurality of arms forming a constraint to elongation of the compliance element. 
     
     
         6 . A system as in  claim 1 , wherein the first tool holds the first compliance element in a desired tension. 
     
     
         7 . A system as in  claim 1 , wherein the first constraining tool applies a compressive force to the first compliance element. 
     
     
         8 . A system as in  claim 7 , wherein the compressive force is variable. 
     
     
         9 . A system as in  claim 1 , wherein the first constraining tool does not limit extension or elongation of the first compliance element until the first compliance element has extended or elongated by the first pre-determined amount. 
     
     
         10 . A system as in  claim 1 , wherein the first constraining tool is adjustable so as to vary the desired position, tension or the range. 
     
     
         11 . A system as in  claim 1 , further comprising:
 a second compliance element coupled with the tether structure and configured to elastically elongate as tension is applied through the tether structure; and   a second constraining tool releasably coupled with the second compliance element so as to hold the second compliance element in a second desired position and allow a second predetermined amount of elastic elongation of the second compliance element as tension is applied to the second compliance element through the tether structure, and   wherein the first and the second constraining tools are releasably and symmetrically coupled together so as to facilitate alignment and positioning of the first and the second compliance elements on opposite sides of a midline of the spinal segment.   
     
     
         12 . A system as in  claim 11 , wherein the first and the second constraining tools are movable relative to one another along one degree of freedom, thereby accommodating spinous processes of varying thicknesses. 
     
     
         13 . A system as in  claim 11 , wherein the first or the second compliance element comprises a locking mechanism, and at least one of the first or the second constraining tools comprise an elongate shaft having a lumen adapted to receive and align a driver or other tool concentrically with the locking mechanism. 
     
     
         14 . A system as in  claim 11 , wherein the first or the second compliance element releasably locks with the first or the second constraining tool. 
     
     
         15 . A system as in  claim 13 , wherein the first or the second constraining tool is adapted to provide a counter torque when the locking mechanism is actuated.