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Screw insertion in osteoporotic bone: turn-of-the-nut and torque-based techniques provide similar resistance to bone
Simon C Mears1, Evan R Langdale, Stephen M Belkoff
1Department of Orthopaedic Surgery, The Johns Hopkins Bayview Medical Center/Johns Hopkins University and the Johns Hopkins International Center for Orthopaedic Advancement, Baltimore, MD.
Objectives:
To measure the resistance to plate slippage provided by a screw inserted to various torsional and rotational endpoints.
Materials And Methods:
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.
Results:
The force required to slip the plate for 180 degrees of screw rotation was not significantly greater than that of the other insertion groups.
Conclusions:
Inserting screws 180 degrees after seating can be expected to yield plate contact to bone similar to that of the "2-fingers tight" standard.