Failure of femoral neck system in Pauwels type III fracture: a fractography and finite element study

• Four FNS implants failed in Pauwels type III fractures within 2–3 months post fixation. • Fractographic and subject-specific FE analyses examined failure mechanisms. • Fractography showed ductile–brittle features in two cases and fatigue in other two. • High stress occurred in cortical screws near the side plate, coinciding failure sites. The femoral neck system (FNS) is an internal fixation device for treating femoral neck fractures. We observed four instances of single-hole FNS failure in Pauwels type III fractures within two to three post-operative months. In each case, the cortical screw failed near the side plate. The fractured surfaces were analysed using scanning electron microscopy, and subject-specific finite element (FE) models were developed from preoperative CT scans to investigate stresses and strains in implants and bones to assess the failure risks and their locations. While cases 1 and 2 exhibited a combination of ductile and brittle failure, with leafy-like structures and cleavage facets, respectively, cases 3 and 4 showed fatigue failure, evident from parallel striations. For all cases, β-phase particles were dispersed within an α-phase matrix. The FE simulations confirmed elevated stresses in the cortical screws near the single-hole side plate, correlating with the clinically observed failure. These results indicate that single-hole FNS might not offer adequate stability for Pauwels type III fractures. The fractographic and FE analysis performed in the current study provides valuable insights into the failure mechanisms of the FNS and highlighting the need for improved implant design for enhanced stability and better clinical outcomes.