Fatigue testing of a self-compression screw model in Pauwels III fracture: an in vitro analysis

Femoral neck fractures (FNFs) have become increasingly common among young adults as a result of high-energy trauma. Despite the variety of implants available for the surgical treatment of FNFs, compelling evidence of clinically uniform outcome is lacking, and high complication rates are still reported. In this scenario, it seems reasonable to investigate novel implants and surgical, especially in Pauwels type III (PIII) FNFs. The objective of this study was to describe the fatigue test results of a construct using the self-compression screw model (X-PIN + P) in PIII FNFs within a validated synthetic bone model.

Sawbones® composite femurs were divided into three groups corresponding to 40% (G40 (n = 4)), 50% (G50 (n = 4)), and 70% (G70 (n = 2)) of the mean load values. The test termination endpoints were catastrophic failure (CF) of the construct, displacement of 10 mm, or reaching 500,000 cycles (C500). The variables analysed were the number of cycles up to 5 mm of displacement (C5 mm), total number of cycles up to termination endpoints (TC), and the mode of CF.

In the G40, the test was terminated due to C500 in three specimens and CF in one specimen (peri-implant subtrochanteric fracture with main screw breakage). The test was terminated due to CF in all models in G50 (peri-implant subtrochanteric fracture without screw breakage in three specimens, and varus collapse of the femoral head in one specimen) and in G70 (femoral head fracture without screw breakage in both specimens).

In vitro fatigue bench testing of the self-compression screw model X-PIN + P in PIII FNFs yield satisfactory numerical results regarding test termination due to the limit total number of cycles (500,000). Catastrophic failures were more frequently observed in the G50 and G70 after supraphysiologic loads, mainly characterized by a subtrochanteric femur fracture.