Abstract / Summary
Abstract Introduction: Long bone nonunion is conventionally treated as a uniform disease entity regardless of anatomical location. However, upper and lower extremities differ fundamentally in biomechanics, soft tissue envelope, vascularity, and open fracture risk. We hypothesized that these differences give rise to distinct clinical nonunion phenotypes.
Methods: Retrospective cohort study of 213 consecutive long bone nonunions treated at a Level 1 trauma center (2007–2018). Patients were stratified by anatomical location into upper extremity (UE, n = 74, 34.7%) and lower extremity (LE, n = 139, 65.3%) nonunions. Groups were compared regarding demographics, comorbidities, fracture characteristics, infection rates, operative burden, laboratory parameters, and treatment strategies. Multivariate logistic regression identified independent predictors of septic nonunion and high revision burden (≥ 3 operations).
Results: Lower extremity nonunion demonstrated a markedly higher infection and reconstructive burden. Septic nonunion was 3.4 times more frequent in the LE group (27.3% vs. 8.1%; p = 0.002). Open fractures were significantly more common (30.9% vs. 6.8%; p < 0.001). The LE group required significantly more revision and follow-up operations (3.3 ± 5.0 vs. 1.4 ± 1.1; p < 0.001), had a higher rate of two-stage procedures (27.3% vs. 4.1%; p < 0.001), and more frequently needed BMP augmentation (12.9% vs. 1.4%; p = 0.004). Despite these differences, demographics, BMI, comorbidity burden, leukocyte counts, and implant loosening rates did not differ. On multivariate analysis, lower extremity location was an independent predictor of septic nonunion (OR 2.80, 95% CI 1.04–7.54; p = 0.042), alongside open fracture (OR 3.01; p = 0.021) and BMI (OR 1.07; p = 0.011).
Conclusion: Upper and lower extremity nonunions represent distinct clinical phenotypes. Lower extremity nonunion is characterized by a substantially higher infection-driven reconstructive burden, likely reflecting the biomechanical demands, limited soft tissue coverage, and greater open fracture risk inherent to the lower limb. These findings support anatomically stratified risk assessment and treatment planning.