Bone screws and particular applications to sacroiliac joint fusion

Abstract

Procedures for the fusion of the sacroiliac joint advantageously make use of an implant selected to distract the joint upon insertion and to maintain or increase tension upon insertion. The implant can have a varying structure along its length. In some method described herein for fusing the sacroiliac joint using an implant, an implant is screwed into the sacroiliac joint between the sacrum bone and the iliac bone. The implant comprises a shaft, a tool engagement flange at top end of the shaft, a pointed tip comprising no more than about 20 percent of the length of the screw, and threads spiraling around the shaft. For screws of particular interest, the volume displacement perpendicular to the shaft increases at least about 5 percent from a point adjacent the tip to a point near the top of the shaft. Some of the desirable screw designs can be used in other orthopedic application, especially situations involving varying bone hardness. Useful filler material can be formed from a blend of bone powder and bioactive agents.

1 . A method for fusing the sacroiliac joint, the method comprising:
 drilling a bore into the joint between the sacrum bone and iliac bone to prepare the joint for insertion of an implant;   selecting a threaded implant based on the prepared joint that distracts the joint upon insertion and maintains or increases tension upon insertion, wherein the implant has a varying structure along its length; and   inserting the implant into the bore within the sacroiliac joint between the sacrum bone and iliac bone to immobilize the joint.   
   
   
       2 . The method of  claim 1  wherein the drilling process comprises the use of a drill tool and wherein the drill tool is tapered. 
   
   
       3 . The method of  claim 1  wherein the implant has a diameter at least about  0 . 5  millimeters wider than the drilled bore at full implantation into the joint. 
   
   
       4 . The method of  claim 1  wherein the selecting process is performed using a threaded sizing element engaging a torque wrench wherein the threaded element is tightened to reach a selected value of torque. 
   
   
       5 . The method of  claim 1  wherein the selecting process comprises choice of a thread design based on bone hardness around the bore. 
   
   
       6 . The method of  claim 1  wherein the implant is tapered and headless. 
   
   
       7 . The method of  claim 1  further comprising placement of bone material within a joint space between the sacrum bone and iliac bone. 
   
   
       8 . The method of  claim 1  wherein the threads of the implant vary along the length of the implant. 
   
   
       9 . The method of  claim 1  wherein implant comprises two sets of interwoven threads. 
   
   
       10 . The method of  claim 8  wherein implant has a tip and top end at the opposite end from the tip, the top end comprising a tool engagement flange and wherein the lateral extent of the threads increases toward the top end of the implant relative to the thread structure near the tip. 
   
   
       11 . A method for fusing the sacroiliac joint using an implant, the method comprising screwing an implant into the sacroiliac joint between the sacrum bone and the iliac bone wherein the implant comprises a shaft, a tool engagement flange at top end of the shaft, a pointed tip comprising no more than about 20 percent of the length of the screw, and threads spiraling around the shaft, wherein the volume displacement perpendicular to the shaft increases at least about 5 percent from a point adjacent the tip to a point near the top of the shaft. 
   
   
       12 . The method of  claim 11  wherein the shaft is tapered to increase in diameter toward the top relative to the tip over at least a portion of the shaft. 
   
   
       13 . The method of  claim 11  wherein the shaft has a cylindrical section between the tip and the top and wherein the increase in differential volume results from an increase in thread diameter from the tip to the top. 
   
   
       14 . The method of  claim 11  wherein the thickness of the thread increases from the tip to the top. 
   
   
       15 . The method of  claim 11  wherein the thickness and diameter of the threads increases from the tip to the top. 
   
   
       16 . The method of  claim 11  wherein the thread spacing decreases from the tip to the top. 
   
   
       17 . A medical implantable screw comprising a headless shaft, a tool engagement flange at top end of the shaft, a pointed tip comprising no more than about 20 percent of the length of the screw, and threads spiraling around the shaft, wherein the volume displacement of the thread increases at least about 5 percent from a point adjacent the tip relative to a point near the top of the shaft and wherein the screw comprises one or more biocompatible materials. 
   
   
       18 . The medical implantable screw of  claim 17  wherein the thread thickness increases from the tip to the top of the shaft. 
   
   
       19 . The medical implantable screw of  claim 17  wherein the lateral extent of the thread increases from the tip to the top of the shaft. 
   
   
       20 . The medical implantable screw of  claim 17  wherein the thread spacing decreases from the tip to the top of the shaft. 
   
   
       21 . A method for inducing bone in-growth for joint fusion or bone repair, the method comprising placing a blend of a bone powder and a bioactive agent that induces bone growth into a joint or bone fracture. 
   
   
       22 . The method of  claim 21  wherein the bioactive agent comprises bone morphogenic protein. 
   
   
       23 . The method of  claim 21  wherein the bone powder comprises demineralized bone powder. 
   
   
       24 . The method of  claim 21  wherein the bone powder comprises a synthetic bone material. 
   
   
       25 . A composition comprising a blend of bone powder and a bioactive agent that simulates bone growth. 
   
   
       26 . The composition of  claim 25  further comprising a biocompatible carrier. 
   
   
       27 . A method for inserting an orthopedic implant into a bone, the method comprising placing a sizing element into a prepared location for a bone screw and tightening the sizing element with a torque wrench to evaluate the size of appropriate bone screw for implantation into the site. 
   
   
       28 . An orthopedic implant comprising a bone replacement materials and a bone growth stimulating biologically active agent, wherein the bone replacement material is a bio-resorbable polymer, a natural or synthetic bone composition or a combination thereof and wherein the biologically active agent is blended into the bone replacement material composition. 
   
   
       29 . The orthopedic implant of  claim 28  wherein the bone replacement material comprises demineralized bone powder, crushed bone, coral, hydroxyapatite, calcium phosphate, calcium sulfate or a combination thereof and the biologically active agent is bone morphogenic protein.