Surgical tether apparatus and methods of use

Abstract

Methods and apparatus for controlling flexion in a spinal segment of a patient include performing a spinal fusion procedure on a pair of adjacent vertebrae in the spinal segment and implanting a constraint device into the patient. Adjusting length or tension in the constraint device allows the constraint device to provide a force a force resistant to flexion of the spinal segment undergoing fusion. The constraint device also modulates loads borne by the spinal segment undergoing fusion or tissue adjacent thereto.

1 . A method for controlling flexion in a spinal segment of a patient, said method comprising:
 providing a constraint device comprising at least one compliance member and at least one tether, wherein the at least one compliance member comprises an elastic member, and wherein the at least one tether comprises an upper tether portion and a lower tether portion with the at least one compliance member coupled therebetween;   performing a spinal fusion procedure on a pair of adjacent vertebrae in the spinal segment, wherein the pair of adjacent vertebrae comprises a superior vertebra and an inferior vertebra, the superior vertebra having a spinous process with a superior surface and the inferior vertebra having a spinous process with an inferior surface;   implanting a constraint device into the patient, wherein the step of implanting comprises coupling the constraint device with the spinal segment,   and wherein the coupling comprises engaging the upper tether portion with the superior surface and engaging the lower tether portion with the inferior surface or a sacrum.   
     
     
         2 . The method of  claim 1 , wherein the constraint device provides an elastic force resistant to flexion of the spinal segment. 
     
     
         3 . The method of  claim 2 , wherein the elastic force encourages the spinal segment to fuse in a position consistent with a natural lordotic curve of the patient. 
     
     
         4 . The method of  claim 1 , wherein the step of performing the spinal fusion procedure comprises posterolateral grafting of the adjacent vertebrae. 
     
     
         5 . The method of  claim 1 , wherein the step of performing the spinal fusion procedure comprises intervertebral grafting in a disc space between the pair of adjacent vertebrae. 
     
     
         6 . The method of  claim 5 , wherein the intervertebral grafting comprises applying bone grafting material to the spinous process of the superior vertebra and the spinous process of the inferior vertebra. 
     
     
         7 . The method of  claim 1 , wherein the step of performing the spinal fusion procedure comprises implanting a first prosthesis into the patient, the first prosthesis engaged with at least a portion of the spinal segment, wherein the constraint device modulates loads borne by the first prosthesis or tissue adjacent thereto. 
     
     
         8 . The method of  claim 1 , wherein implanting the first prosthesis comprises positioning an intervertebral device between the pair of adjacent vertebrae, the intervertebral device configured to maintain an alignment and a distance between the pair of adjacent vertebrae during a development of arthrodesis. 
     
     
         9 . The method of  claim 8 , wherein the intervertebral device comprises an interbody fusion cage. 
     
     
         10 . The method of  claim 7 , wherein implanting the first prosthesis comprises positioning bone grafting material between the pair of adjacent vertebrae. 
     
     
         11 . The method of  claim 10 , wherein the bone grafting material is selected from the group consisting of an allograft, an autograft, a synthetic graft, and a xenograft. 
     
     
         12 . The method of  claim 7 , wherein the first prosthesis or the constraint device comprises a therapeutic agent adapted to modify tissue in the spinal segment. 
     
     
         13 . The method of  claim 12 , wherein the therapeutic agent comprises a bone morphogenic protein. 
     
     
         14 . The method of  claim 1 , wherein implanting the constraint device occurs without implanting a prosthesis directly in an interspinous region extending between an inferior surface of the spinous process of the superior vertebra and a superior surface of the spinous process of the inferior vertebra or the sacrum. 
     
     
         15 . The method of  claim 1 , wherein the step of implanting the constraint device comprises:
 piercing an interspinous ligament to form a penetration superior to the superior surface of the spinous process of the superior vertebra; and   advancing the upper tether portion through the penetration.   
     
     
         16 . The method of  claim 1 , wherein the step of implanting the constraint device comprises:
 advancing the upper tether portion through a gap between the spinous process of the superior vertebra and an adjacent process, the gap created by surgical removal of an interspinous ligament therefrom.   
     
     
         17 . The method of  claim 1 , wherein the step of implanting the constraint device comprises:
 piercing an interspinous ligament to form a penetration inferior to the inferior surface of the spinous process of the inferior vertebra; and   advancing the lower tether portion through the penetration.   
     
     
         18 . The method of  claim 1 , wherein the step of implanting the constraint device comprises:
 advancing the lower tether portion through a gap between the inferior surface of the spinous process of the inferior vertebra and an adjacent spinous process or a sacrum, the gap created by surgical removal of an interspinous ligament therefrom.   
     
     
         19 . The method of  claim 1 , wherein the compliance member has a spring constant, the method further comprising selecting the spring constant such that the elastic force provides enough resistance to flexion so that fusion can occur between the pair of adjacent vertebra, while at the same time allowing for micromotion between the pair of adjacent vertebrae. 
     
     
         20 . The method of  claim 1 , wherein loading, other than tensile loading, is not transferred to the constraint device. 
     
     
         21 . The method of  claim 1 , wherein implanting the constraint device is performed without resecting tissue of the spinal segment. 
     
     
         22 . The method of  claim 1 , wherein implanting the constraint device is performed without resecting bone tissue of the spinal segment.