Tip-to-apex distance does not predict fixation failure regardless of reduction quality in intra-capsular neck of femur fractures treated with femoral neck system

Femoral neck system (FNS) is a novel fixed-angle gliding device combining a sliding bolt and an anti-rotational screw to treat femoral neck fractures. It was proven to have comparable biomechanical strength to sliding hip screws. Tip-to-apex distance (TAD) is an established assessment for fixation quality in sliding hip screws. The purpose of our study was to evaluate whether TAD can be used in FNS implant to predict fixation failure. Seventy-six patients receiving FNS fixation for intra-capsular hip fracture were included. TAD was measured from post-operative radiographs and clinical outcomes were collected with a mean follow-up of 14.1 months. The mean TAD for patients who experienced fixation failure was 20.7 mm, versus 19.7 mm for those who did not (p = 0.395). Subgroup analysis among fractures with good reduction quality, defined as no varus angulation, less than 5 degrees of retroversion, and less than 4 mm cortical translation, did not demonstrate statistically significant difference in the mean TAD between failure and non-failure group (20.7 mm vs 19.5 mm, p = 0.68). We conclude that in our study of modest sample size, there was not demonstrable association between TAD and fixation failure in intra-capsular neck of femur patients treated with FNS.