Comparison of Fatigue Performance Between Fully and Partially Threaded Cannulated Screws Used for Stabilization of Slipped Capital Femoral Epiphyses.

Cannulated screws are widely used for the treatment of slipped capital femoral epiphysis; however, the optimal choice and number of implants have not been clearly defined. Studies have shown that two screws are biomechanically superior to a single screw in load-to-failure testing, but the fatigue performance of different screw designs has not been investigated. This study compared the fatigue characteristics of fully and partially threaded cannulated screws. Partially and fully threaded 7.3-mm screws were subjected to cyclic loading on a custom testing fixture. Screws were tested in three-point bending, with a force between 20 N and 780 N applied at 10 Hz. Cycles to failure were recorded, as well as force and displacement data. Partially threaded screws had statistically higher cycles to failure than fully threaded screws (p $=$ .001). Partially threaded screws demonstrated higher cycles to failure when subjected to loading, suggesting greater resistance to fatigue failure under similar clinical conditions.