Residual Positive Buttress Displacement After Femoral Neck System Fixation for Acute Femoral Neck Fractures: A Retrospective Cohort Study
Jian Xing, Yanan Ren, Pengfei Wang, Kun ZhangABSTRACT
Objective
When anatomical reduction cannot be safely achieved, the functional relevance of residual positive‐buttress displacement after FNS fixation remains uncertain. Few clinical studies have quantified how its magnitude relates to hip function. To determine whether hip function after femoral neck system fixation differs by postoperative reduction pattern and, within positive‐buttress reduction, by residual medial cortical displacement.
Methods
This retrospective cohort study included 180 adults with isolated acute femoral neck fractures treated with femoral neck system fixation between September 1, 2023, and April 30, 2024, and followed for at least 12 months. The overall analysis included Garden I–IV fractures; the exploratory five‐group displacement analysis was restricted to Garden I–III fractures. Postoperative reduction was classified as anatomical reduction, positive‐buttress reduction, or negative‐buttress reduction. Positive‐buttress displacement was measured on anteroposterior radiographs and categorized as PR‐2 (≤ 2 mm), PR‐4 (> 2–4 mm), or PR‐6 (> 4 mm). The primary outcome was 12‐month Harris Hip Score. Group comparisons used one‐way analysis of variance, Kruskal–Wallis tests, chi‐square or exact tests, and multivariable linear regression. Multivariable linear regression adjusted for age, sex, and Garden classification. Additional analyses evaluated continuous displacement, retained Garden IV fractures in the five‐group comparison, and incorporated the available clinical covariates.
Results
The cohort included 45 anatomical, 98 positive‐buttress, and 37 negative‐buttress reductions. Median 12‐month Harris Hip Score was 95.8, 86.0, and 69.5, respectively. Compared with anatomical reduction, adjusted Harris Hip Score was lower by 9.40 points in positive‐buttress reduction and 25.62 points in negative‐buttress reduction. In the exploratory analysis restricted to Garden I‐III fractures, median Harris Hip Score declined across anatomical reduction, PR‐2, PR‐4, PR‐6, and negative‐buttress reduction (95.8, 90.0, 80.0, 74.0, and 68.9). Among the 82 positive‐buttress cases in this restricted analysis, each additional millimeter of displacement was associated with a 3.89‐point lower score (95% confidence interval, 3.12–4.66 points lower). The additional five‐group analysis retaining Garden IV fractures showed the same direction of association.
Conclusions
In the overall cohort, reduction pattern was associated with 12‐month hip function. Garden IV fractures and open reduction were unevenly distributed across reduction patterns, and adjustment cannot eliminate residual confounding from fracture complexity, reduction difficulty, surgeon decisions, and unmeasured factors; these associations do not show that changing reduction pattern improves function. In the exploratory analysis restricted to Garden I‐III fractures, PR‐2 had the highest 12‐month Harris Hip Score among the nonanatomical groups. Larger residual displacement was associated with lower scores, but the findings do not establish a clinical 2‐mm threshold or a clinically important PR‐2 versus anatomical reduction difference. The additional all‐Garden analysis does not constitute separate validation in Garden IV fractures. PR‐2, PR‐4, and PR‐6 were exploratory categories rather than validated clinical thresholds or indications for additional reduction or open surgery.