Cortical, anti-migration, facet dowel for fusion of facet joints in the spine and devices for setting the same in place

Abstract

A novel allograft is provided for insertion into a prepared site between adjacent spinal facets. The allograft or facet dowel is typically comprised of three portions, a partially spherical body defining a spherical segment, a nose portion, and a tail portion, all aligned along a longitudinal axis. In addition, a set of instruments is provided for the excavation of an allograft placement site between the two facets. The set of instruments includes a T-spade drill which will, in conjunction with a normal drill, excavate a site for the emplacement of the allograft. A novel method of using the instruments and the allograft is also provided.

1 . A drill for use in conjunction open spinal facet implant surgery wherein the facet implant comprises a substantially rigid spherical segment having a diameter Ds; a tail segment comprising a cylindrical shape joined at a first end and integral to the spherical segment and having a removed end, the tail segment having a longitudinal axis, a diameter Dt, and a length Lt; and a nose segment comprising a cylindrical shape and a removed end, the nose segment integral with the spherical segment at a near end and having a length Ln, a longitudinal axis coincident with the longitudinal axis of the tail segment, and a diameter Dn, the drill comprising:
 a nose portion comprising a cylindrical shape;   a tail portion comprising a cylindrical shape, wherein the diameters of the nose portion and the tail portion are approximately the same as the diameter of the nose segment of the facet implant; and   a body portion having a thickness substantially less than the diameter of the nose portion, and having a width about the same as the diameter of the spherical segment of the facet implant.   
     
     
         2 . The drill of  claim 1 , wherein the cylindrical shape of the nose portion of the drill has a diameter of approximately 4 mm. 
     
     
         3 . The drill of  claim 1 , wherein the thickness of the body portion of the drill is approximately 1.5 mm. 
     
     
         4 . The drill of  claim 1 , wherein the width of the body portion of the drill is approximately 6 mm. 
     
     
         5 . The drill of  claim 1 , wherein the length of the body portion of the drill is approximately 4.5 mm. 
     
     
         6 . The drill of  claim 1 , wherein the cylindrical shape of the nose portion of the drill has a diameter of approximately 4 mm, the thickness of the body portion of the drill is approximately 1.5 mm, the width of the body portion of the drill is approximately 6 mm, the length of the body portion of the drill is approximately 4.5 mm, and the cylindrical shape of the tail portion of the drill has a diameter of approximately 4 mm. 
     
     
         7 . The drill of  claim 1 , further comprising an elongated shaft coupled to the tail portion of the drill at a first end of the shaft, the elongated shaft sized to place the body portion of the drill between opposing spinal facets while extending outside of an associated facet joint and to provide torque to rotate the body portion to remove bone from opposing spinal facets. 
     
     
         8 . The drill of  claim 7 , further comprising:
 a working channel through which the shaft extends, the shaft having a second end that extends from the working channel remotely from the drill, wherein the first end of the shaft tapers to the tail portion; and   a T-handle at the second end of the shaft, the T-handle sized to allow a user to apply torque to the shaft.   
     
     
         9 . A drill for use in conjunction with open spinal facet implant surgery, the drill comprising:
 a nose portion having a thickness wider than a pre-surgery distance between opposing spinal facets;   a tail portion having a thickness approximately the same as the nose portion; and   a body portion having a thickness substantially less than the thickness of the nose portion and having a width substantively greater than the thickness of the nose portion.   
     
     
         10 . The drill of  claim 9 , wherein the thickness of the nose portion is approximately 4 mm. 
     
     
         11 . The drill of  claim 9 , wherein the nose portion comprises a cylindrical shape. 
     
     
         12 . The drill of  claim 11 , wherein the cylindrical shape of the nose portion has a diameter of approximately 4 mm. 
     
     
         13 . The drill of  claim 9 , wherein the thickness of the body portion is approximately 1.5 mm. 
     
     
         14 . The drill of  claim 9 , wherein the width of the body portion is approximately 6 mm. 
     
     
         15 . The drill of  claim 9 , wherein the tail portion is cylindrical in shape. 
     
     
         16 . The drill of  claim 15 , wherein the cylindrical shape of the tail portion has a diameter of approximately 4 mm. 
     
     
         17 . The drill of  claim 9 , wherein the length of the body portion is approximately 4.5 mm. 
     
     
         18 . The drill of  claim 9 , wherein the thickness of the nose portion is approximately 4 mm, the thickness of the body portion is approximately 1.5 mm, the width of the body portion is approximately 6 mm, the length of the body portion is approximately 4.5 mm, and the thickness of the tail portion is approximately 4 mm. 
     
     
         19 . The drill of  claim 9 , further comprising an elongated shaft coupled to the tail portion at a first end of the shaft, the elongated shaft sized to place the body portion between opposing spinal facets while extending outside of an associated facet joint and to provide torque to rotate the body portion to remove bone from opposing spinal facets. 
     
     
         20 . The drill of  claim 19 , further comprising:
 a working channel through which the shaft extends, the shaft having a second end that extends from the working channel remotely from the drill, wherein the first end of the shaft tapers to the tail portion; and   a T-handle at the second end of the shaft, the T-handle sized to allow a user to apply torque to the shaft.