Spondylolisthesis correction apparatus and method

Abstract

An apparatus and method are provided that allow for the realignment and stabilization of adjacent vertebrae. An implant of this invention both repositions adjacent vertebrae and remains in situ to maintain the new position. The implant has two halves which are interlocked such that they can slide horizontally with respect to each other. Movement of the implant halves and their respective positions are controlled by set screw within the implant. The implant includes radial anchors which fit into alignment slots made in the misaligned vertebra by the disclosed method. The set screws are used to advance the halves of the implant which in turn move the misaligned vertebrae back into correct positions. The correct position of the vertebrae is locked in place through a nut and a plate.

1 . A system for correcting alignment between two vertebrae caused by spondylolisthesis comprising:
 a distractor having a distractor body with a hollow channel along a distractor body longitudinal axis, an anterior end, a posterior end having first a first distractor arm and a second distractor arm which extend from the distractor body in the direction of the distractor body longitudinal axis, the first distractor arm extending parallel to the distractor body longitudinal axis having a first distractor stop surface perpendicular to the distractor body longitudinal axis, the second distractor arm extending parallel to the distractor body longitudinal axis having second distractor stop surface perpendicular to the distractor body longitudinal axis, a gap between the first distractor stop surface and the second distractor stop surface, a measurement scale along the first distractor arm, and a torque handle perpendicularly attached to the distractor body;   an impactor having an impactor handle, an impactor body having an impactor longitudinal axis, an impactor latitudinal axis, an impactor body anterior end, and an impactor body posterior end, the impactor handle being centered on the latitudinal axis of the impactor body anterior end, an impactor seat centered along the latitudinal axis of the impactor body posterior end;   the impactor seat fitting within the gap on the distractor;   a gate having a gate longitudinal axis, a gate latitudinal axis, an interior channel along the gate longitudinal axis with a distractor end and a saw end, the distractor end having a distractor entrance to the interior channel and having a distractor stop, the saw end having a saw entrance to the interior channel, a top side, a bottom side, a right sidewall, a left sidewall, a first set of guide slots extending from about the center of the right sidewall to about the center of the bottom side and parallel to the saw end, a second set of guide slots extending from about the center of the left sidewall to about the center of the top side and parallel to the saw end, a first handle guide slot at about the center of the right sidewall extending along the right sidewall from the saw end and connecting to the first set of guide slots and terminating in a first handle stop, a second handle guide slot at about the center of the left sidewall extending along the left sidewall from the saw end and connecting to the second set of guide slots and terminating in a second handle stop, the first set of guide slots having a first set spacing and the second set of guide slots having a second set spacing, the first set spacing related to the second set spacing by a third set spacing;   a saw with a saw longitudinal axis, the saw having a saw handle jointed to a spindle shaft, a saw guide body, and a saw guide post, the saw guide post joined to the saw handle at an angle generally perpendicular to the saw longitudinal axis, the saw guide body having a longitudinal spindle hole coaxial with the saw longitudinal axis, the spindle shaft rotatively mounted in the longitudinal hole, the saw guide body further having a horizontal saw alignment stop and a vertical saw alignment stop, the saw handle having a handle housing, a motor rigidly mounted in the handle housing, a drive shaft connected to and driven by the motor, the drive shaft extending through a hole in the handle housing and the spindle shaft, a transmission housing rigidly attached to the spindle shaft, a transmission located within the transmission housing, the transmission operatively connected to the drive shaft and to a chuck, the chuck releasably fixed to a mill bit, a mounting plate attached to the transmission housing, the mill bit movable between a stoppage position dictated by the mounting plate engagement with the horizontal saw alignment stop and an operational position dictated by the mounting plate engagement with the vertical saw alignment stop;   an implant having a first half having a first body with a first longitudinal axis, a first threaded collar, a first channel, a first mating interconnection, a first outer surface and a first set of radial anchors, the first set of radial anchors radially extending generally perpendicularly from the first outer surface, a second half having a second body with a second longitudinal axis, a second threaded collar, a second channel, a second mating interconnection, a second outer surface and a second set of radial anchors, the second set of radial anchors radially extending generally perpendicularly from the second outer surface, the first half and the second half slidably connected by the first mating interconnection and the second mating interconnection, the first body and the second body connected to form an implant body, the first threaded collar and the second threaded collar connected to form an implant collar with a first thread pitch, the first channel and the second channel connected to form an implant channel, the first channel being threaded with a set of channel threads, a set screw having an outside perimeter and a spanner slot, the outside perimeter being threaded with a set of set screw threads, the set screw located in the implant channel, the set of channel threads in engagement with the set of set screw threads, the set of channel threads and the set of set screw threads having a pre-determined relationship to allow the first half to move a pre-determined distance in relation to the second half when the set screw is rotated a pre-determined angle of rotation, the first set of radial anchors and the second set of radial anchors being generally parallel;   an inserter having a top half and a bottom half, the top half further having a top longitudinal axis and a top mating guide along the top longitudinal axis, the top half having a first semi-cylindrical section and a first semi-hexagonal section, the bottom half having a bottom longitudinal axis and a bottom mating channel along the bottom longitudinal axis, the bottom half having a second semi-cylindrical section and a second semi-hexagonal section, the top half and the bottom half slidingly connected along the top mating guide and the bottom mating channel creating a cylindrical section and a hexagonal section, the top half having a connection end, the connection end having a threaded implant channel; the threaded implant channel having a second thread pitch;   the first thread pitch matching the second thread pitch;   a guide block having a guide block longitudinal axis, a guide block top connected to guide block bottom, and a guide hole centered through the guide block longitudinal axis;   a nut having a nut head and a nut body, the nut body being generally perpendicular to the nut head, the nut body having a threaded hole, the threaded hole having a third thread pitch;   the first thread pitch matching the third thread pitch; and   a plate having a plate nut hole, a plurality of plate screw holes, and a front, a back, and the plate nut hole having a front diameter and a back diameter.   
     
     
         2 . The system of  claim 1  wherein the front diameter is larger than the back diameter. 
     
     
         3 . The system of  claim 1  wherein the first implant half further comprises a first set of alignment marks and the second implant half further comprises a second set of alignment marks and the first set of alignment marks align with the second set of alignment marks when the first set of radial anchors is parallel with the second set of radial anchors. 
     
     
         4 . The system of  claim 1  wherein the first distractor arm includes a first distractor point guide having a first rounded surface and the second distractor arm includes a second distractor point guide having a first angled surface. 
     
     
         5 . The system of  claim 1  wherein the nut head includes a set of spanner holes. 
     
     
         6 . The system of  claim 1  wherein the gate has a visual indicator indicating a gate orientation for the distractor. 
     
     
         7 . The system of  claim 1  wherein the measurement scale has a plurality of markings spaced 1 mm apart. 
     
     
         8 . The system of  claim 1  wherein the impactor handle has a centerline which is parallel to a horizontal axis of the impactor body. 
     
     
         9 . The system of claim of  claim 4  wherein the impactor seat has a second rounded surface. 
     
     
         10 . A system of tools for inserting an implant for correcting a spondylolisthesis condition between two affected vertebrae comprising:
 a distractor having a distractor body with a hollow channel along a distractor body longitudinal axis, an anterior end, a posterior end having first a first distractor arm and a second distractor arm which extend from the distractor body in the direction of the distractor body longitudinal axis, the first distractor arm having a first tapering end and a first stop surface perpendicular to the distractor body longitudinal axis, the second distractor arm having a second tapering end and a second stop surface perpendicular to the distractor body longitudinal axis, the first tapering end and the second tapering end tapering in height by a set tapering degree, a gap between the first stop surface and the second stop surface, and a torque handle attached to the distractor body;   an impactor having a striking end, a posterior end, and an impactor body, the impactor body having a tapering end, the tapering end tapering in height by the set tapering degree;   the impactor fitting within the hollow channel of the distractor;   a gate having a gate longitudinal axis, a gate latitudinal axis, an interior channel along the gate longitudinal axis with a distractor end and a saw end, the distractor end having a distractor entrance to the interior channel and having a distractor stop, the saw end having a saw entrance to the interior channel, a top side, a bottom side, a right sidewall, a left sidewall, a first set of guide slots extending from about the center of the right sidewall to about the center of the bottom side and parallel to the saw end, a second set of guide slots extending from about the center of the left sidewall to about the center of the top side and parallel to the saw end, a first handle guide slot at about the center of the right sidewall extending along the right sidewall from the saw end and connecting to the first set of guide slots and terminating in a first handle stop, a second handle guide slot at about the center of the left sidewall extending along the left sidewall from the saw end and connecting to the second set of guide slots and terminating in a second handle stop, the first set of guide slots having a first set spacing and the second set of guide slots having a second set spacing, the first set spacing related to the second set spacing by a third set spacing;   the anterior end of the distractor fitting within the distractor entrance and adjacent to the saw entrance;   a saw with a saw longitudinal axis, the saw having a handle joined to a spindle shaft, the handle having a handle housing, a motor rigidly mounted in the handle housing, a drive shaft connected to and driven by the motor, the drive shaft extending through a hole in the handle housing and the spindle shaft, a saw guide projection joined to the handle at an angle generally perpendicular to the saw longitudinal axis, the saw guide body further having a longitudinal pivot hole coaxial with the longitudinal axis, the spindle shaft rotatively mounted in the longitudinal pivot hole, a transmission housing rigidly attached to the spindle shaft, a transmission located within the transmission housing, the transmission operatively connected to the drive shaft and to a chuck, the chuck releasably fixed to a mill bit, the transmission housing further comprising an index means for limiting the rotation of the transmission housing with respect to the guide body, the mill bit movable between a stoppage position and an operational position;   the saw guide body fitting within the saw entrance of the gate and the hollow channel of the distractor;   an implant adapted to be fitted between the two affected vertebrae having a first half having a first half longitudinal axis, a first half outer surface, and a first joint and a second half having a second half longitudinal axis, a second half outer surface, and a second joint, the first half and the second half connected by the first joint and the second joint forming an implant body, the implant body further having a frustroconical shape, the frustroconical shape tapered by the set tapering degree, the first half having a first channel and the second half having a second channel such that when the first half and the second half are connected the first channel and the second channel form an implant chamber in the implant body, a drive bolt located inside the implant chamber having a first set of threads, the first channel being threaded, a second set of threads, the first half having a first set of radial anchors extending substantially perpendicularly from the first half outer surface and the second half having a second set of radial anchors extending substantially perpendicularly from the second half outer surface;   the first set of threads engaging the second set of threads;   an inserter having a top half and a bottom half, the top half having a top longitudinal axis and a top joint along the top longitudinal axis, the bottom half having a bottom longitudinal axis and a bottom joint along the bottom longitudinal axis, the top half and the bottom half slidingly connected along the top joint and the bottom joint, the top half having a connection end, the connection end releasably connectable to the implant body;   a nut having a nut head and a nut body, the nut body being perpendicular to the nut head, the nut body having an implant hole, releasably connectable to the implant body;   a plate connectable to the two affected vertebrae having a plate hole through which passes the nut body.   
     
     
         11 . The system of  claim 10  wherein the implant body further comprises a set of indexing marks on the first implant half and the second implant half. 
     
     
         12 . The system of  claim 10  wherein the gate further comprises a pointing means for tactically discerning a direction of insertion. 
     
     
         13 . The system of  claim 10  wherein the distractor further comprises a measurement scale along the first longitudinal extension. 
     
     
         14 . The system of  claim 10  where the guide body further comprising a horizontal blade stop and a vertical blade stop. 
     
     
         15 . The system of  claim 10  further comprising a set of gates wherein each gate in the set of gates has a different third set spacing. 
     
     
         16 . The system of  claim 10  further comprising a set of distractors, wherein each distractor of the set of distractors has a unique height. 
     
     
         17 . The system of  claim 10  further comprising a set of impactors, wherein each impactor of the set of impactors has a unique height. 
     
     
         18 . The system of  claim 10  further comprising a set of saw guide bodies, wherein each saw guide body of the set of saw guide bodies has a unique height. 
     
     
         19 . The system of  claim 10  further comprising a set of implants, each of the set of implant bodies having a unique diameter. 
     
     
         20 . The system of  claim 10  wherein the set tapering degree is a range from approximately 2 degrees to approximately 10 degrees.