Laboratory testing of bolts and screws in cancellous bone

The pull-out resistance of 6.5-mm cancellous screws and 4.0-mm bolts with 12-mm washers from cancellous beef bone was measured. The findings are the following: (1) The 4.0-mm bolt with the 12-mm washer had greater pull-out resistance from thin (12-mm thick) cancellous bone than did the 6.5-mm cancellous screw. (2) In thicker cancellous bone (35 mm), the bolt and washer had greater pull-out resistance than did the screw, but the difference is not significant. (3) There was no significant difference in pull-out resistance of the cancellous screw from holes drilled with a 3.2- or a 4.5-mm bit. These findings support the use of bolts for fixation of thinner sections of cancellous bone, but not when the bolt or screw is in thicker cancellous bone.