Comparative efficacy of different anti-shortening screws in preventing postoperative shortening in displaced femoral neck fractures: a retrospective cohort study

Femoral neck fractures are common with high complication rates. Postoperative shortening is a significant issue, causing functional decline and increased avascular necrosis risk. The Femoral Neck System (FNS) is widely used but has a high shortening risk. Anti-Shortening Screws (ASS) have been introduced to address this, with varying efficacy by design. This retrospective cohort study compared the clinical effects of no ASS, single-threaded ASS, and double-threaded ASS in preventing shortening in displaced femoral neck fractures treated with FNS. Patients aged 18-65 years with Garden III/IV fractures and a minimum follow-up of 12 months were included. Primary outcome was femoral neck shortening distance, with secondary outcomes including hip function recovery (Harris Hip Score and Parker Score), surgical time, intraoperative blood loss, and complication rates. A total of 147 patients were included (49 in each group). The double-threaded ASS group had significantly less shortening at all follow-up time points (p < 0.05). At 1 year, mean shortening distances were 2.4 ± 0.3 mm (double-threaded), 3.8 ± 0.6 mm (single-threaded), and 4.8 ± 0.7 mm (traditional) (p = 0.007). Incidence of moderate to severe shortening (≥ 5 mm) was 2.0% (double-threaded), 14.3% (single-threaded), and 28.6% (traditional) (χ² = 16.390, p = 0.003). The double-threaded group had higher Harris Hip Scores (median: 93.9 vs. 90.7 and 88.7; p < 0.001) and Parker Mobility Scores (median: 9.0 vs. 9.0 and 8.0; p = 0.002). Complication rates were similar among groups. Double-threaded ASS is more effective in reducing shortening and improving hip function than single-threaded ASS and traditional FNS fixation. Future research should include long-term follow-up and randomized trials.