Selected Postoperative Neck-Shaft Angle in Proximal Femoral Osteotomy Can Affect the Bone Healing: A Finite Element Study

Proximal femoral osteotomy (PFO) is a surgical correction of proximal femoral deformity. Surgical choices, notably the postoperative neck-shaft angle (NSA), can affect postoperative stability and healing. While NSA's role in femoral mechanics is recognized, its impact on bone healing remains unclear. To determine the influence of postoperative NSA on bone healing; to investigate the interaction of healing-related parameters and mechanical safety. Medical imaging, gait data, and surgical information from nine patients (10 femurs) were used to build personalized finite element models of PFO-implanted femurs. Three postoperative neck-shaft angles (128°, 135°, 143°) were tested. During simulated walking, interfragmentary movement, deviatoric strain, mechanical stimulus, bone-implant micromotion, and peak von Mises stress (PVMS) were evaluated. Healing mode (primary vs. secondary) was classified based on interfragmentary movement thresholds. Mono-modal healing (primary in four and secondary in three) was observed in seven femurs, independent of postoperative NSA. In three femurs, a transition from primary to secondary healing occurred with increased NSAs. The PVMS for the implant and the bone exceeded critical values across all NSA for two femurs, and micromotion was deemed critical only at 128° in two femurs. This study highlights the value of integrating patient-specific modelling into preoperative planning. Bone healing modes were sensitive to postoperative NSA in 30% of cases, while 70% exhibited a single healing mode across the tested angles. Overall, findings suggest the need to simultaneously consider the complex interaction between NSA and subject-specific factors on mechanical safety and healing outcomes following PFO. • Patient-specific neuromusculoskeletal modelling and finite element analysis. • Postoperative NSA can affect the healing rate and type and risk of surgery. • NSA variation alters interfragmentary motion, shifting healing mode in some cases. • There is a trade-off between healing stimuli and surgical risks. • Subject-specific mechanics dictate optimal NSA, not one-size-fits-all surgery.