The impact of physiological load and support conditions on axial implant system testing of locking plates for femoral shaft fractures – a biomechanical analysis

Objectives: This study aimed to determine the impact of physiological loading and boundary conditions on the biomechanical performance of a plating system for femoral shaft osteosynthesis via axial implant system testing (IST). Specifically, the effects of rotational load boundary conditions and realistic gait-based load patterns were evaluated to understand their influence on the biomechanical response and failure modes of the implant system. Methods: Two test configurations – Fix-Free, featuring a rotational joint, and Fix-Fix, with fixed support at both ends – were subjected to static and cyclic loading. Cyclic testing incorporated sinusoidal and gait-based load patterns, reflecting the physiological axial joint load during walking. In total, 30 test samples (n=30), employed by a bone surrogate and the plate-screw system in bridge-plating state, were tested via axial IST. Results: The Fix-Free configuration exhibited significantly lower axial stiffness and load capacity reductions of 60.8 % compared to Fix-Fix in static testing. Under cyclic gait-based loading, both setups experienced progressive screw-plate interface failures, with earlier degradation observed in Fix-Free. Conclusions: Findings indicate a strong impact of physiological load patterns and boundary conditions. The results support the need for standards and guidelines for biomechanical testing of osteosynthetic plating systems via IST with universal physiological boundaries.