Expansion Screw Bone Tamp

Abstract

A method of compacting and stabilizing bone in the spine using an expandable screw and bone filler. The method comprises placing an expanding screw through a pedicle and into a fractured vertebral body using established techniques; and expanding the screw within the body to create a cavity by tamping bone around the expanded aspect of the screw. The screw can be expanded and rotated about its rotational-axis to tamp bone adjacent to the expanded screw. After compaction, the screw is removed and the cavity is filled with bone filler.

We claim: 
     
         1 . A bone tamp comprising:
 a) an elongated shaft having a distal portion, an external thread and a proximal head, a longitudinal bore extending along the longitudinal axis of the shaft, an internal thread being provided in the bore, a distal portion of the bore being provided with a tapered recessed portion, and the shaft also having a plurality of slits extending parallel to the longitudinal direction of the shaft to produce a plurality of shaft legs,   b) a second shaft inserted into the longitudinal bore and having a threaded surface cooperating with the internal thread in the bore,   c) a mandrel received in the distal portion of the bore and being larger in size than the bore,   wherein the mandrel and the second shaft are inserted into the longitudinal bore as a unit, with the mandrel being a distal portion of the unit and the second shaft being the proximal portion of the unit,   whereby proximal movement of the mandrel into the bore splays the shaft legs from the elongated shaft at different angles.   
     
     
         2 . The tamp of  claim 1  wherein the mandrel has a first proximal side having a first taper angle and a second proximal side having a second larger taper angle. 
     
     
         3 . The tamp of  claim 1  wherein the mandrel comprises mandrel-halves that are capable of independent axial movement. 
     
     
         4 . The tamp of  claim 1  wherein the mandrel comprises staggered tapers characterized by a first proximal side having a first taper that extends proximally a first distance and a second proximal side having a second taper that extends proximally a second longer distance. 
     
     
         5 . The tamp of  claim 1  wherein the plurality of legs comprise a first leg having a first length and a second leg having a second longer length. 
     
     
         6 . The tamp of  claim 1  wherein the elongated shaft is a bone screw comprising a cannulated, threaded shaft. 
     
     
         7 . The tamp of  claim 6  wherein the slits in the cannulated, threaded shaft form at least three legs. 
     
     
         8 . The tamp of  claim 6  wherein the bone screw further comprises a mandrel having a distal end portion having a diameter larger than the bore, wherein the expanding step comprises moving the mandrel proximally within the threaded, cannulated shaft. 
     
     
         9 . The tamp of  claim 8  wherein the distal end portion of the mandrel comprises a tapered proximal portion. 
     
     
         10 . The tamp of  claim 8  wherein the mandrel has an asymmetric radial geometry that causes preferential leg deflection. 
     
     
         11 . The tamp of  claim 8  wherein the cannulated, threaded shaft has a geometry that causes preferential leg deflection. 
     
     
         12 . The tamp of  claim 11  wherein the geometry includes a feature selected from the group consisting of a ramp, a tooth, a divot, a thinned shaft wall, and a thickened shaft wall. 
     
     
         13 . The tamp of  claim 12  wherein the feature is a ramp. 
     
     
         14 . The tamp of  claim 12  wherein the feature includes at least two ramps. 
     
     
         15 . The tamp of  claim 14  wherein the ramps are serially nested. 
     
     
         16 . The tamp of  claim 6  wherein a first leg has an elasticity, a second leg has an elasticity, and the elasticity of the first leg is greater than the elasticity of the second leg. 
     
     
         17 . The tamp of  claim 6  made of a biocompatible metal. 
     
     
         18 . The tamp of  claim 17  wherein the screw further comprises a threaded bushing that enables rotation of a first portion of the cannulated, threaded shaft without producing rotation of a second portion of the shaft. 
     
     
         19 . The tamp of  claim 17  wherein the elongated shaft comprises a segment of threads that engages the vertebral body but does not rotate when the expanded screw is rotated, thereby avoiding longitudinal movement of the screw during rotation. 
     
     
         20 . The tamp of  claim 6  wherein the legs of the elongated shaft have substantially no screw threads thereon. 
     
     
         21 . The tamp of  claim 6  wherein the elongated threaded shaft comprises a plurality of deep threads. 
     
     
         22 . The tamp of  claim 6  wherein the elongated, threaded shaft comprises a plurality of shallow threads. 
     
     
         23 . The tamp of  claim 5  wherein the screw comprises a structural mesh surrounding the shaft. 
     
     
         24 . A bone tamp comprising:
 a) an elongated shaft having a distal portion, an external thread and a proximal head, a longitudinal bore extending along the longitudinal axis of the shaft, an internal thread being provided in the bore, a distal portion of the bore being provided with a tapered recessed portion, and the shaft also having a plurality of slits extending parallel to the longitudinal direction of the shaft to produce a plurality of shaft legs,   b) a second shaft inserted into the longitudinal bore and having a threaded surface cooperating with the internal thread in the bore,   c) a mandrel received in the distal portion of the bore and being larger in size than the bore,   wherein the mandrel and the second shaft are inserted into the longitudinal bore as a unit, with the mandrel being a distal portion of the unit and the second shaft being the proximal portion of the unit,   whereby proximal movement of the mandrel into the bore splays the shaft legs from the elongated shaft at different angles,   wherein at least the plurality of shaft legs comprise a shape memory metal and are characterized by a linear memorized shape.