INFLUENCE OF CUTTING TECHNOLOGY ON INITIAL FIXATION STRENGTH AND THREAD QUALITY OF DIFFERENT BONE PINS

A comparison of the fixation strength was made for the Steinmann, Denh am, and the Apex commercial bone pins, which have different drilling e nd geometry and self-tapping thread design. Additional tests were made to assess the effects of pre-drilling with an orthopaedic twist drill bit prior to pin insertion. Peak pull-out force and pin displacement were measured for these pins inserted into the distal metaphysis of hu man cadaveric tibiae. The quality of thread reproduction in the bone r esulting from the cutting process was assessed from thread profiles of negative moulds cast into the threaded holes. The Apex pins had simil ar pull-out forces to the Denham pins, despite their smaller diameter. Values for both pins were significantly greater than those for the St einmann pin. The thread profiles showed that the Denham pin caused sub stantial damage to the cortical bone and formed poor quality threads i n the cancellous bone. The Apex pin formed a better thread, which was improved further by the use of a pre-drilled pilot hole.