A finite element model to simulate intraoperative fractures in cementless hip stem designs

Intraoperative femur fractures are a complication of hip arthroplasty, strongly related to the cementless stem design; this kind of fracture is not always recognised during surgery, and revision surgery may be necessary. The present study aimed to simulate intraoperative crack propagation during stem implantation using subject-specific quasi-static finite element models. Eleven subject-specific finite element femur models were built starting from CT data, and the implant pose and size of a non-commercial cementless stem were identified. The model boundary conditions were set with a compressive load from 1000 N to 10 000 N, to simulate the surgeon's hammering, and element deactivation was used to model the crack propagation. Two damage quantifiers were analysed to identify a threshold value that would allow us to assess if a fracture occurred. A methodology to assess the primary stability of the stem during insertion was also proposed, based on a push-out test. Crack propagation up to the surface was obtained in six patients; in two cases there was no crack generation, while in three patients the crack did not reach the external surface. This study demonstrates the possibility to simulate the propagation of the fracture intraoperatively during hip replacement surgery and generate quantitative information about the bone damage using a virtual cohort of simulated patients with anatomical and physiological variability.