Purpose: Transverse patella fractures (TPF) have historically been repaired via internal fixation with stainless steel (SS) wire based on the tension band principle. However, heavy suture has been shown to be a viable and promising alternative to SS in such procedures. Double strand FiberWire® (FW) tied with a Wagoner’s Hitch has been previously shown to have greater strength in tension band fixation than 18-guage SS wire. However, fatigue testing of FW has yet to be investigated for the treatment of TPF. This study aims to compare the fatigue strength of double strand FW tied with a Wagoner’s Hitch, to the current gold standard of treatment using SS wire with two (bilateral) compression twists.
Methods: A novel 3-point-bending patella model, designed to simulate a worse case loading scenario, was used for the fatigue testing of the two different wire constructs. The patella model has a convex surface, similar to a human patella, and has two parallel holes drilled along its length to allow for reproducibility of the surgical technique. Each wire was used to bind the halves of the simulated TPF together prior to fatigue testing. The FW was tied using a Wagoner’s Hitch, while the SS wire was bound with two compression twists, each having seven twists. Once bound, each of the patella constructs was subjected to cyclical three-point-bending at 90%, 60% and 30% of the maximum strength reported for the SS wire. Furthermore, a 100N pre-load force was applied to maintain the wire in constant tension during fatigue testing. Based on published findings, fixation failure was defined as a 3mm gap at the apex of the convexity.
Results: With each loading cycle, fatigue damage in the SS wire accumulates leading to gradual increases in permanent deformation. In contrast, the FW is able to withstand damage, returning closer to its original length, for many more loading cycles. Furthermore, comparing the force-deformation curves between the SS wire and FW constructs, a softening occurs for the SS while a hardening behavior is exhibited by the FW.
Conclusions: The FW construct is superior to the SS construct in fatigue, withstanding a greater number of cycles before failure. The combination of increased strength, previously reported, and the current findings, suggests FW to be superior to SS for the fixation of TPF.