Screw insertion in osteoporotic bone: turn-of-the-nut and torque-based techniques provide similar resistance to bone plate slippage.

Abstract

To measure the resistance to plate slippage provided by a screw inserted to various torsional and rotational endpoints. A 7-hole, 3.5-mm narrow dynamic compression plate was affixed to an osteoporotic humeral shafts using screws inserted: (1) to 90 degrees after plate contact, (2) to 180 degrees after plate contact, (3) by the 1.4-N·m torque limit method, and (4) by the "2-fingers tight" method. The resistance of the plate to sliding against the bone was measured using a materials testing machine. We checked for an effect of screw insertion method on bone-plate slippage with a general linearized latent and mixed model, controlling for bone mineral density, sex, and specimen clustering. Significance was set at P < 0.05. The force required to slip the plate for 180 degrees of screw rotation was not significantly greater than that of the other insertion groups. Inserting screws 180 degrees after seating can be expected to yield plate contact to bone similar to that of the "2-fingers tight" standard.