Should nails be locked dynamically or statically in atypical femoral fractures? – A radiological analysis of time to union and reoperations in 236 displaced fractures with 4 years average follow-up

Abstract

<h3>Introduction</h3><p>Atypical femoral fractures (AFFs) are associated with delayed union and higher reoperation rates. Axial dynamization of intramedullary nails is hypothesized to reduce time-to-union (TTU) and fixation failure as compared to static locking.</p><h3>Methods</h3><p>Consecutive acutely displaced AFFs fixed with long intramedullary nails across five centres between 2006 and 2021 with a minimum postoperative follow-up of three months were retrospectively reviewed. The primary outcome was TTU, compared between AFFs treated with dynamically or statically locked intramedullary nails. Fracture union was defined as a modified Radiographic Union Score for Tibial fractures score of 13 or greater. Secondary outcomes involved revision surgery and treatment failure, defined as non-union beyond 18 months or revision internal fixation for mechanical reasons.</p><h3>Results</h3><p>A total of 236 AFFs (127 dynamically locked and 109 statically locked) were analysed with good interobserver reliability of fracture union assessment (intraclass correlation coefficient = 0.89; 95% CI = 0.82–0.98). AFFs treated with dynamized nails had significantly shorter median TTU (10.1 months; 95% CI = 9.24–10.96 vs 13.0 months; 95% CI = 10.60–15.40) (log-rank test, <em>p</em> = 0.019). Multivariate Cox regression revealed that dynamic locking was independently associated with greater likelihood of fracture union within 24 months (<em>p</em> = 0.009). Reoperations were less frequent in the dynamic locking group (18.9% vs 28.4%), although the difference was not statistically significant (<em>p</em> = 0.084). Static locking was an independent risk factor for reoperation (<em>p</em> = 0.049), as were varus reduction and lack of teriparatide use within three months of surgery. Static locking also demonstrated a higher frequency of treatment failure (39.4% vs 22.8%, <em>p</em> = 0.006) and was an independent predictor of treatment failure in logistic regression (<em>p</em> = 0.018). Other factors associated with treatment failure included varus reduction and open reduction.</p><h3>Conclusions</h3><p>Dynamic locking of intramedullary nails in AFFs is associated with faster time to union, lower rate of non-union, and fewer treatment failures.</p>