Multi-thread bone screw and method

Abstract

A bone screw comprises a threaded shank including a distal end portion and a proximal end portion, and defining a first threaded section extending from the distal end portion toward the proximal end portion and adapted for anchoring in cancellous bone. A second threaded section extends contiguously from the first threaded section toward the proximal end portion. The second threaded section has a finer thread pattern relative to the first threaded section. In one embodiment, the first threaded section includes a first helical threading defining a single lead thread pattern for anchoring in cancellous bone, and the second threaded section includes a second helical threading interleaved with the first threading to define a duel lead thread pattern for engagement in cortical bone. In a further embodiment, the bone screw includes a head portion extending from the threaded shank and configured for coupling to a spinal implant.

1 - 40 . (canceled). 
     
     
         41 . A system comprising:
 a screw comprising:
 a threaded shank including a distal end portion and a proximal end portion, said threaded shank defining a first threaded section extending from said distal end portion toward said proximal end portion, said threaded shank defining a second threaded section extending contiguously from said first threaded section toward said proximal end portion, said threaded shank including a first helical threading extending along said threaded shank from said first threaded section and into said second threaded section, said threaded shank including a second helical threading interleaved with said first helical threading to define said second threaded section; and 
   a structure comprising an inner first region having a first hardness and an outer second region having a second hardness, the second hardness being greater than the first hardness,   wherein said screw is configured for being inserted into said structure such that said first threaded section penetrates said first region after said first threaded section penetrates said second region.   
     
     
         42 . The system of  claim 41 , wherein said second threaded section comprises a finer thread pattern relative to said first threaded section. 
     
     
         43 . The system of  claim 41 , wherein each of said first and second helical threadings having a substantially equal thread pitch. 
     
     
         44 . The system of  claim 41 , further comprising a spinal rod positioned in U-shaped channel in a head portion of said screw that extends from said proximal end portion. 
     
     
         45 . The system of  claim 41 , wherein said second threading is interleaved with and substantially centered between said first threading to define a double helical thread pattern. 
     
     
         46 . The system of  claim 41 , wherein said second threading is offset about 180 degrees relative to said first threading. 
     
     
         47 . The system of  claim 41 , wherein said first threading and the second threading are buttress threads. 
     
     
         48 . The system of  claim 41 , wherein said first threaded section extends along at least about two-thirds of said threaded shank. 
     
     
         49 . The system of  claim 41 , wherein said second threaded section extends along about one-thirds of said threaded shank. 
     
     
         50 . The system of  claim 41 , wherein:
 said first threaded section extends along at least about two-thirds of said threaded shank; and   said second threaded section extends along about one-thirds of said threaded shank.   
     
     
         51 . The system of  claim 41 , wherein said screw comprises a head portion that extends from said proximal end portion, said head portion comprising a pair of spaced apart arms that together with a surface of said head portion define a U-shaped channel. 
     
     
         52 . The system of  claim 51 , wherein said U-shaped channel is concavely curved between the arms. 
     
     
         53 . The system of  claim 51 , wherein said threaded shank extends along a longitudinal axis, said screw being coaxial with said longitudinal axis from said proximal end portion to said head portion. 
     
     
         54 . The system of  claim 51 , further comprising a set screw having a threaded outer surface, wherein inner surfaces of said arms are threaded and are configured to engage the threaded outer surface to couple said set screw to said head portion. 
     
     
         55 . The system of  claim 41 , wherein said first threaded section has a larger thread depth than said second threaded section. 
     
     
         56 . A system, comprising:
 a screw comprising:
 a threaded shank including a distal end portion, a proximal end portion, and a middle portion extending between said distal end portion and said proximal end portion, 
 a first helical buttress threading extending continuously from said distal end portion to said proximal end portion of said threaded shank, 
 a second helical threading extending from said middle portion to said proximal end portion such that said second helical threading does not extend to said distal end portion, said first and second helical threadings having a substantially similar thread pitch, and 
 a head portion extending from said proximal end portion of said threaded shank; and 
   a structure comprising an inner first region having a first hardness and an outer second region having a second hardness, the second hardness being greater than the first hardness,   wherein said screw is inserted into said structure such that said first helical threading penetrates said first region after said first helical threading penetrates said second region.   
     
     
         57 . The system of  claim 56 , wherein said second threading is substantially centered between said first threading to define said double helical thread pattern that engages said second region. 
     
     
         58 . The system of  claim 56 , wherein said second threading is offset about 180 degrees relative to said first threading. 
     
     
         59 . The system of  claim 56 , wherein said second threading is a buttress thread. 
     
     
         60 . A system comprising:
 a screw comprising:
 a threaded shank including a distal end portion and a proximal end portion, said threaded shank defining a first threaded section extending from said distal end portion toward said proximal end portion, said threaded shank defining a second threaded section extending contiguously from said first threaded section toward said proximal end portion, said threaded shank including a first helical threading extending along said threaded shank from said first threaded section and into said second threaded section, said threaded shank including a second helical threading interleaved with said first helical threading to define said second threaded section, and 
 a head portion extending from said proximal end portion of said threaded shank, said head portion comprising a pair of spaced apart arms that together with a surface of said head portion define a U-shaped channel that is concavely curved between the arms; 
   a structure comprising an inner first region having a first hardness and an outer second region having a second hardness, the second hardness being greater than the first hardness; and   a set screw having a threaded outer surface, wherein inner surfaces of said arms are threaded and are configured to engage the threaded outer surface to couple said set screw to said head portion,   wherein said screw is configured for being inserted into said structure such that said first threaded section penetrates said first region after said first threaded section penetrates said second region.