BIOMECHANICAL ASSESSMENT OF COMPRESSION SCREWS

A series of mechanical tests on anatomic specimen cancellous bone and cancellous bonelike foam were conducted to evaluate and compare an Acu trak compression screw with an AO 4-mm cancellous screw and the Herber t screw. The Acutrak and AO screws produced similar fragment compressi on in foam and bone; Acutrak and AO compression were significantly gre ater than that of the Herbert screw. However, Acutrak was able to main tain compression after cyclic loading significantly better than were t he AO and Herbert screws. The pushout force of Acutrak and AO screws w ere significantly greater than that of the Herbert screw in foam and b one. The torque required to break fragment contact was significantly g reater for the Acutrak than for the AO or Herbert screws, but that for the AO was greater than that for the Herbert screw. The results of th is analysis show the Acutrak screw is capable of producing and maintai ning compression between bone fracture fragments, In addition, the Acu trak screw ,vas shown to have superior mechanical characteristics than did Herbert screw in every mode tested. The Acutrak screw did not sur pass the fragment compression achieved by the AO screw in foam, but it did not overtighten or experience degradation of compression after 50 0 cycles of simulated physiologic loading.