HOLDING POWER OF 3.5 MM VERSUS 4.0 MM SCREW APPLICATIONS PLACED IN STRIPPED 2.7 MM SCREW SITES

Mechanical stripping of orthopaedic screws is a complication that can occur during plate fixation of fractures. This report compares the hol ding power of 3.5 mm cortical and 4.0 mm cancellous orthopaedic screws inserted as a salvage technique in stripped 2.7 mm screw sites in cad aver bone. Both 3.5 mm and 4.0 mm orthopaedic screws were applied with and without tapping to stripped screw sites in the diaphysis of matur e canine tibiae. Mechanical testing of the pull-out force required to extract these screws showed that all of the applications have comparat ive holding powers, but the 4.0 mm screw had significantly greater hol ding power when compared with the 3.5 mm screw. Tapping the stripped s crew site, prior to placing the 3.5 mm or 4.0 mm screw, did not signif icantly affect the holding power. The 4.0 mm cancellous screw has the advantages of significantly greater holding power and less interferenc e with the 2.7 mm dynamic compression plate, when compared to the 3.5 mm cortical screw.