cortical screw

screw

1. a mechanical device for fixing one object to another, characterized by a spiral ridge cut on the external surface of a cylindrical rod of decreasing diameter towards its point. This is a male screw. In a female screw the screw is cut on the inside of a cylindrical cavity.

2. a colloquial term for a worn out or inferior horse.

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AISF bone screw

see buttress thread bone screw.

buttress thread bone screw

the thread is not a simple V as in the standard thread but has one side of the groove at right angles to the direction of the screw and the other side at a 45° angle. Called also AISF, Howmett compression, Richards-Bechtol.

cancellous bone screw

has a coarse thread; threaded to only the first third of the length of the screw.

cortical screw

threaded the full length of the screw; fine thread to hold in dense bone.

Howmett compression bone screw

see buttress thread bone screw.

lag bone screw

used as a compressing unit between two fragments with the first half of the screw near the point threaded, with the diameter of the ridges greater than that of the unthreaded half near the head. As the ridged part of the screw bites in the walls of the drill hole in the distal fragment, the unthreaded part is free to move within the drill hole in the proximal fragment, thus compressing the two pieces of bone together.

Richards-Bechtol bone screw

see buttress thread bone screw (above).

standard bone screw

with a V thread the full length of the screw, with a single slot, cruciate or Phillips head.

transfixation screw

orthopedic screw used to reattach bone fragments to a solid skeletal part. The proximal part near the head is not threaded and needs to be of a smaller diameter than the threaded portion nearer the tip.

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cortical screw

Orthopedics A type of orthopedic hardware used to provide fixation by itself or in conjunction with other devices; CSs have fine threads along the shaft and are designed to anchor in cortical bone. See Screw. Cf Cancellous screw.