Comparison of Cortical and Cancellous Screws for Sternal Fixation

The goal of this study is to compare the performance of currently available screw types and configurations for rigid sternal fixation. Bone fixation plates were attached to osteoporotic human sternum with cortical or cancellous screws in either a unicortical or bicortical manner. The plates were cyclically loaded transversely (0–50N at 2Hz) for 15,000 cycles; the resulting lateral screw displacement was measured continuously. Bicortical attachment allowed significantly lower initial displacement than unicortical (p = 0.015), whereas cortical screws allowed significantly lower displacement than cancellous screws after long term cycling (p = 0.039). These initial findings indicate that both screw type and cortical purchase are important parameters in the design of a rigid plating system for sternal closure. Cortical screws appear to be more applicable to the osteoporotic sternum, as the cortical shell regions support more screw purchase than the degenerated cancellous part, and bicortical screw purchase appears to decrease screw loosening.