Early mechanical failure patterns after femoral neck fixation with the femoral neck system and dynamic hip screw.

BACKGROUND

The Femoral Neck System (FNS) has been introduced as a minimally invasive alternative to the Dynamic Hip Screw (DHS) for intracapsular femoral neck fracture fixation. Comparative data on early mechanical failure patterns remain limited.

PURPOSE: To describe the early mechanical complications observed after FNS and DHS fixation during a period of progressive FNS adoption, without assuming implant-specific causality.

METHODS

This retrospective single-center cohort included 130 consecutive patients treated between December 2020 and January 2024 (42 DHS, 88 FNS). The primary outcome was mechanical revision within one year. Tip-apex distance (TAD) and postoperative reduction quality using the Garden Alignment Index (GAI) were assessed on immediate postoperative radiographs.

RESULTS

Mechanical revision occurred in 3 DHS patients (7.1%; 95% CI 1.5-19.5%) and 8 FNS patients (9.1%; 95% CI 4.0-17.1%; p = 0.25). Reduction was acceptable in 40/42 DHS and 80/88 FNS patients (p = 0.50). Mechanical failure occurred in 5/10 patients with unacceptable reduction versus 6/120 with acceptable reduction (p < 0.001). Mean TAD was similar between groups (18.8 ± 4.8 versus 19.6 ± 5.2 mm; p = 0.34), and all four cut-outs occurred with TAD >25 mm. Observed failure patterns included shortening/medialization and cut-out after DHS, and shortening/medialization, cut-out, and peri-implant fracture after FNS.

CONCLUSION

Different mechanical complications were observed after DHS and FNS fixation, but confounding by indication and the small number of events preclude implant-specific causal conclusions. Reduction quality and implant positioning appear important determinants of early mechanical failure.