Importance

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Abstract

A generally cylindrical broken bone screw removal device having a trephine assembly located at the distal end and a proximal end adapted to be engaged by a tool for rotating the device. The trephine assembly has a trephine, an alignment pin, and an internal annular cam. The cam is free to rotate independent of the trephine. The internal wall of the cam has a D shaped cross-section which is tapered, i.e. decreases in size from the distal toward the proximal end of the device. The internal diameter of the trephine is eccentric to its outer diameter, and the D shaped cross-section of the cam is eccentric to the internal diameter of the trephine. A broken screw is removed from bone by placing the trephine over the proximal end of the screw and rotating the device while applying pressure to cause the trephine to core bone around the screw, so that the device descends down the body of the screw until the screw to enters the interior of the cam to a depth where it engages the tapered walls of the cam and causes the cam to rotate with respect to the adjacent internal wall of the trephine; and the body of the screw becomes wedged between the cam internal wall of the trephine to transmit torque from the device to the screw to unscrew it from the bone.

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First Claim