The walls of the femoral neck as an auxiliary tool for femoral stem positioning

Background: Femoral anteversion is a major contributor to functionality of the hip joint and is implicated in many joint pathologies. Accurate determination of component version intraoperatively is a technically challenging process that relies on the visual estimation of the surgeon. The following study aimed to examine whether the walls of the femoral neck can be used as appropriate landmarks to ensure appropriate femoral prosthesis version intraoperatively. Methods: We conducted a retrospective study based on 32 patients (64 hips) admitted to our centre between July and September 2020 who had undergone a CT scan of their lower limbs. Through radiological imaging analysis, the following measurements were performed bilaterally for each patient: anterior wall version, posterior wall version, and mid-neck femoral version. Anterior and posterior wall version were compared and evaluated relative to mid-neck version, which represented the true version value. Results: Mean anterior wall anteversion was 20 degrees (95% CI, 17.6-22.8 degrees) and mean posterior wall anteversion was -12 degrees (95% CI, -15 to -9.7 degrees). The anterior walls of the femoral neck had a constant of -7 and a coefficient of 0.9 (95% CI, -9.8 to -4.2; p < 0.0001; R-2 0.77). The posterior walls of the femoral neck had a constant of 20 and a coefficient of 0.7 (95% CI, 17.8-22.5; p < 0.0001; R-2 0.60). Conclusions: Surgeons can accurately obtain femoral anteversion by subtracting 7 degrees from the angle taken between the anterior wall and the posterior femoral condyles or by adding 20 degrees to the angle taken between the posterior wall and the posterior femoral condyles.