Determinants of surgical necessity in Danis-Weber a lateral malleolus fractures: Prognostic insights from a nonoperative cohort.

BACKGROUND

Danis-Weber Type A lateral malleolus fractures are conventionally deemed stable and managed nonoperatively, yet prognostic heterogeneity leads to chronic complications in subsets of patients, revealing limitations in uniform treatment paradigms. This study introduces a novel subclassification to identify soft-tissue-driven risks and refine surgical thresholds in a nonoperative cohort.

METHODS

In this retrospective cohort of 434 skeletally mature patients with acute Danis-Weber Type A fractures initially treated nonoperatively, we subclassified injuries via 3D-CT into Subtype A1 (simple avulsion without medial involvement; n = 350) and Subtype A2 (with medial deltoid ligament injury or medial malleolus fracture; n = 84). Demographics, fracture metrics (e.g., displacement), treatment variables (e.g., brace duration), and ligament status (via MRI in 233 cases) were analyzed. Primary outcomes-nonunion and severe long-term pain (composite: VAS ≥4, ≥2 sprains, or AOFAS <70)-were assessed at ≥ 12 months, using multivariable logistic regression and Kaplan-Meier survival analysis.

RESULTS

Overall union was 95%, but Subtype A2 exhibited markedly worse prognosis: lower union (83% vs. 98%; p < 0.001), inferior 3-month AOFAS scores (82.5 ± 11.8 vs. 90.2 ± 9.5; p < 0.001), and elevated rate of severe pain (35% vs. 20%; p < 0.001) compared to A1. Within A2, A2.2 (medial malleolus fracture; n = 34) fared worse than A2.1 (deltoid injury; n = 50) in union (79% vs. 87%; p = 0.02) and function. Multivariable models pinpointed anterior talofibular ligament (ATFL) injury (OR=3.50, 95% CI 1.40-8.70; p = 0.037) and deltoid injury (OR=4.50, 95% CI 1.80-11.00; p = 0.021) as independent drivers of pain. Displacement associated with nonunion univariately (r = 0.18, p = 0.02) but not multivariately (OR=1.40, p = 0.059). Kaplan-Meier curves confirmed delayed union in A2 (median 6 vs. 4 months; log-rank p = 0.012).

CONCLUSION

Danis-Weber Type A fractures harbor hidden instability, with medial soft-tissue integrity-via A1/A2 subclassification-outweighing displacement as the cardinal outcome predictor. This framework advocates stability-focused strategies, including targeted imaging, cautious rehabilitation, or early surgery for ligamentous compromise, to avert chronic pain and post-traumatic osteoarthritis (PTOA).

LEVEL OF EVIDENCE: Prognostic Level III (retrospective cohort study).