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 Acutrak compression screw with an AO 4-mm cancellous screw and the Herbert screw. The Acutrak and AO screws produced similar fragment compression in foam and bone; Acutrak and AO compression were significantly greater than that of the Herbert screw. However, Acutrak was able to maintain compression after cyclic loading significantly better than were the AO and Herbert screws. The pushout force of Acutrak and AO screws were significantly greater than that of the Herbert screw in foam and bone. The torque required to break fragment contact was significantly greater 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 this analysis show the Acutrak screw is capable of producing and maintaining compression between bone fracture fragments. In addition, the Acutrak screw was shown to have superior mechanical characteristics than did Herbert screw in every mode tested. The Acutrak screw did not surpass the fragment compression achieved by the AO screw in foam, but it did not overtighten or experience degradation of compression after 500 cycles of simulated physiologic loading.