Bone screw

Abstract

A bone screw comprising a shaft having a first set of leading threads and a second set of trailing threads spaced apart from the first set of threads by an unthreaded central portion. The second set of threads are carried externally on a sleeve having a smooth inner cylindrical surface such that the sleeve is slidable about the unthreaded shaft portion. A raised lip is provided about the trailing end of the shaft to retain the sleeve on the shaft. The first and second set of screw threads are like-handed, but preferably of different pitch, with the pitch of the first set of screw threads exceeding that of the second set of screw threads to effectively hold portions of a fractured bone in compressive engagement. Provision of the second set of threads on a slidable sleeve enables the main shaft to slide through the sleeve and back out of the bone, when absorption occurs such as when the invention is used to repair a femoral neck fracture. The ability of the main shaft to back out in a direction opposite the femoral head is an advantage because if the second set of threads were fixed on the main shaft, the bone screw would tend to penetrate the femoral head and enter the joint capsule when absorption occurs, which would cause interference of the joint articulation and pain to the patient.

Dependencies are inferred from the claim text.