Importance

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Abstract

A bone screw is disclosed for joining bone fragments or for mounting a prosthetic component onto an underlying bone. The bone screw includes a head and an elongated cylindrical shank which is integral with and extends from the head. The shank includes a threaded member and a shoulder member connecting the threaded member and the head, the shoulder member having an outer surface with a porous medium thereon for encouraging bone ingrowth fixation. The outer diameter of the shoulder member is greater than the diameter of a bore of the bone into which the screw is to be threadedly engaged. The head of the screw is provided with a coupling member engageable by a tool for selectively rotating the shank to advance the screw into the bone. As the bone screw is advanced toward a fully seated position, the shoulder member with the porous medium thereon engages the bone in a fitting manner which may be described as a 'scratch fit'. Initial loosening of the bone screw due to the viscoelastic relaxation of the bone tissue following fixation is thereby largely inhibited and long term loosening of the bone screw is also inhibited by providing an interface onto which or into which bone tissue can grow to stabilize the repair site or the implanted component.

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First Claim