Spine microsurgery techniques, training aids and implants

Abstract

A minimally invasive, fluoroscopically guided system is disclosed for stabilizing the articular facet joints of adjacent vertebrae. Ring and dowel implants are disclosed for installation into the facet joint. The invention includes a novel spine surgical training aid used in the initial surgeon training process for refreshing the surgeon's perspective of the critical three dimensional anatomy of the vertebrae. The invention also includes a surgical kit having a range of size-specific drills, inserters, impactors and custom-length long k-wires matched to the internal diameter of the instrumentation system.

1 . An implant for stabilizing two adjacent vertebrae of the spine, the adjacent vertebrae having superior and inferior articular processes forming first and second facet joints each having opposing subchondral articular surfaces, the implant comprising:
 a ring configured to be installed into a bone path;   the bone path comprising a cylindrical kerf bored into the opposing articular processes;   the ring having an outer surface configured to create an interference fit with the surrounding bone of the kerf;   wherein the ring constrains facet joint motion through circumferential tension band effect.   
   
   
       2 . An implant as recited in  claim 1 , wherein the outer surface of the ring has an outer diameter sized to create the interference fit with the surrounding bone of the kerf. 
   
   
       3 . An implant as recited in  claim 1 , wherein the outer surface of the ring has a tapered leading edge of the ring. 
   
   
       4 . An implant as recited in  claim 1 , wherein the outer surface of the ring is roughened to create the interference fit with the surrounding bone of the kerf. 
   
   
       5 . An implant as recited in  claim 4 , wherein the roughened external surface of the ring comprises one or more fenestrations, the fenestrations configured to promote growth of cancellous bone through and around the ring implant. 
   
   
       6 . An implant as recited in  claim 5 , wherein the fenestrations comprise parallel columns running axially along the outer cylindrical surface. 
   
   
       7 . An implant as recited in  claim 5 , wherein the fenestrations comprise circular holes running from the outside surface to an inside surface of the ring. 
   
   
       8 . An implant as recited in  claim 5 , wherein the fenestrations have raised edges at their perimeters, the raised edges forming an interference fit with the surrounding bone of the kerf. 
   
   
       9 . An implant as recited in  claim 6 , wherein the external surface comprises a plurality of raised columns extending axially between the fenestrations. 
   
   
       10 . An implant as recited in  claim 1 , wherein the ring is configured for installation into the facet joint via a guide wire. 
   
   
       11 . An implant as recited in  claim 1 , wherein the outside diameter of the ring ranges from about 6 mm to about 12 mm. 
   
   
       12 . An implant as recited in  claim 1 , wherein the ring ranges from about 4 mm to about 12 mm in length. 
   
   
       13 . An implant for stabilizing two adjacent vertebrae of the spine, the adjacent vertebrae having superior and inferior articular processes forming first and second facet joints each having opposing subchondral articular surfaces, the implant comprising:
 a cylindrical body configured to be installed into a bored bone path;   the bone path comprising a cylindrical bore into the opposing articular processes;   the cylindrical body having a surface configured to create an interference fit with the surrounding bone of the bore;   wherein the cylindrical body comprises one or more longitudinal ridges that extend axially at least along a portion of the length of the implant;   the one or more longitudinal ridges extending radially from the diameter of the implant such that the one or more longitudinal ridges extend radially into the bone of the bone path as the implant is guided into the path;   wherein, when installed, the one or more longitudinal ridges are in intimate contact with bone surrounding the one or more longitudinal ridges for at least a portion of the length of the bone path to inhibit rotation of the implant within the bone path and immobilize the first facet joint of the articulation between the adjacent vertebrae against translational and rotational forces imposed on the first facet joint.   
   
   
       14 . An implant as recited in  claim 13 , wherein the one or more longitudinal ridges are positioned on the implant such that the implant is guided axially into the bone path without rotation of the implant with respect to the bone path. 
   
   
       15 . An implant as recited in  claim 13 , wherein the surface of the cylindrical body is tapered from its leading edge. 
   
   
       16 . An implant as recited in  claim 13 , wherein the surface of the cylindrical body is roughened to create the interference fit with the surrounding bone of the bore. 
   
   
       17 . An implant as recited in  claim 13 , wherein the cylindrical body comprises a ring having an axial channel through the length of the body; and
 wherein the bone path comprising a cylindrical kerf bored into the opposing articular processes;   the ring having a surface configured to create an interference fit with the surrounding bone of the kerf.   
   
   
       18 . An implant as recited in  claim 17 , further comprising:
 a plurality of fenestrations along the outer surface of the ring;   wherein the fenestrations extend into the channel such that when the ring is installed in the bone path the fenestrations promote bony ingrowth radially through the fenestrations between bone in the channel and bone surrounding the ring.   
   
   
       19 . An implant as recited in  claim 18 , wherein the fenestrations run longitudinally along the length of the implant and in between the one or more longitudinal ridges. 
   
   
       20 . An implant as recited in  claim 18 , wherein the ring constrains facet joint motion through circumferential tension band effect. 
   
   
       21 . An implant as recited in  claim 13 , wherein the one or more longitudinal ridges are configured to be installed substantially perpendicular to the rotational moment created by the facet joint physiologic stress. 
   
   
       22 . An implant as recited in  claim 13 , wherein the one or more longitudinal ridges are sized to engage the bone path at a location at least along the distal half of the bone path.