Optimal sliding distance in femoral neck system for displaced femoral neck fractures: a retrospective cohort study.

Background: Displaced femoral neck fractures frequently result in considerable patient morbidity, with complications such as postoperative femoral neck shortening occurring in up to 39.1% of cases. This shortening is associated with reduced hip function and mobility. The Femoral Neck System (FNS), which allows for controlled sliding to facilitate fracture reduction and healing, may mitigate these issues. However, the ideal sliding distance to balance fracture healing and minimize complications is not well defined.

Methods: We performed a retrospective cohort study of 179 patients who underwent FNS fixation for displaced femoral neck fractures at our institution from September 2019 to September 2023. Patients were categorized into three groups based on the intraoperative sliding distance allowed by the FNS: the Minimal Slide group (≤ 5 mm), the Moderate Slide group (> 5 to ≤ 10 mm), and the Extensive Slide group (> 10 to 20 mm). Primary outcomes included postoperative femoral neck shortening, the incidence of moderate to severe shortening, time to fracture union, and hip joint function as assessed by the Harris Hip Score (HHS) and the Parker Mobility Score. Secondary outcomes included complication rates such as implant cut-out, nonunion, avascular necrosis of the femoral head, and the need for secondary surgery.

Results: The Extensive Slide group of moderate to severe shortening at 32.31%, which was 1.59-fold and 8.88-fold that of the Moderate Slide (20.34%) and Minimal Slide group's (3.64%), respectively (P < 0.01). The sliding predominantly occurred within the first three months postoperatively and had substantially ceased by six months. At one year postoperatively, the median shortening was 2.7 mm (IQR, 0.7 to 3.5 mm) for the Minimal Slide group, a value that was notably lower compared to the 3.2 mm (IQR, 2.4 to 4.6 mm) for the Moderate Slide group and the 3.5 mm (IQR, 1.3 to 8.1 mm) for the Extensive Slide group. The average time to achieve union was similar across all groups, with no significant differences. Functional outcomes, as assessed by the Harris Hip Score (HHS) and the Parker Mobility Score, the Harris Hip Score (HHS) demonstrated statistical significance, the Parker Mobility Score did not reach statistical significance.

Conclusions: Restricting FNS slide to ≤ 5 mm in surgery may reduce shortening, improve hip function, and not hinder fracture healing or implant stability. Considering the key 3-month sliding timeline postoperatively is advisable in clinical practice. Further research with a broader patient cohort is vital to confirm these findings and to anchor them in evidence-based practice.