Is the tip-apex distance a reliable predictor of implant failure in surgical fixation of femoral neck fractures with the synthes femoral neck system device?

BACKGROUND: The Tip-Apex Distance (TAD) is known to affect outcomes of traditional implants such as sliding hip screws (SHS). However, it is unclear if the TAD has the same effect on the Femoral Neck System (FNS). This study aimed to assess if the TAD is a predictor of FNS failure and report outcomes of FNS at our institution. METHODS: This retrospective, single-centre study included 46 patients who underwent FNS for femoral neck fractures (FNF) between 2017 and 2022. Radiographic and clinical factors were analysed. Outcomes reported include intra-operative duration, length of hospitalization and failure rate. Failure was defined as the presence of complications like cut-out, breakage, avascular necrosis (AVN) or neck shortening. Scale data were analysed with Unpaired Student T-test and Mann-Whitney U test. Categorical data were assessed with Pearson χ2 or Fischer's exact test where appropriate. Binary logistic regression was performed for risk factors. RESULTS: Mean age was 69.6 years old. Mean follow-up was 20.4 months. Median operation duration was 53.5 minutes. Median length of stay was 9 days. Failure rate was 15.2% (n = 7), consisting of two cut-outs, three AVN, one neck shortening and one distal screw breakage. Re-operation rate was 8.7% (n = 4). Mean TAD was 16.8 mm and 18.1 mm in the failure and non-failure groups respectively (P = 0.431) and was not a significant risk factor for failure on logistic regression testing (p = 0.444). Osteoporotic BMD value was more prevalent in the failure group (71.4%) but was not a significant risk factor for failure on logistic regression (P = 0.056). Quality of reduction, age, body mass index (BMI) and pre-operative Garden's score were also insignificant on logistic regression. (P > 0.05) CONCLUSION: The TAD is not a reliable predictor of FNS implant failure for treatment of FNFs. Overall, the FNS is a reliable device with a low failure rate, a short operative time, and a short length of stay comparable to that reported in the literature and with traditional implants.