Ankle fractures are prevalent in adult orthopaedics, with isolated Weber B lateral malleolar fractures, which comprise about 60% of cases. Treatment depends on the congruency of the ankle mortise; congruent fractures usually get non-operative care by cast immobilisation. Unstable fractures are generally surgically treated to avert complications because of ligamentous injuries. A diagnostic challenge increases as some congruent ankles can be unstable upon stress testing, which creates variability in surgical practices. Although surgery is commonly performed, evidence indicates long-term advantages over casting in stress-positive, yet congruent Weber B fractures are scarce. This uncertainty was the impetus for the SUPER-FIN trial, designed to compare the efficacy of cast immobilization versus surgery for this type of fracture.
The aim of this SUPER-FIN trial was to determine whether cast immobilization is non-inferior to surgical fixation in terms of functional result at 2 years in patients with isolated Weber B ankle fractures, which are radiographically congruent at presentation, but deemed unstable on external rotation stress testing. Secondary outcomes include comparing pain, ankle-specific function, health-related quality of life, range of motion, radiographic outcomes (fracture union, ankle congruity, and post-traumatic osteoarthritis), and treatment-related adverse events between the two treatment strategies.
SUPER-FIN was a prospective, randomised, parallel-group non-inferiority trial conducted at Oulu University Hospital, Finland, between January 2013 and July 2021. Skeletally mature patients (≥16 years) with isolated unimalleolar Weber B fibula fractures and a congruent ankle mortise on initial radiographs were screened. Stability was evaluated by using a standardised external rotation stress test under fluoroscopy. Fractures were unstable if the medial clear space measured ≥5 mm. Eligible patients were randomised 1:1 to either cast immobilisation for 6 weeks or surgical fixation by using sealed opaque envelopes prepared by an independent statistician.
The primary result was the Olerud-Molander Ankle Score (OMAS range 0 to 100) at 2 years. A non-inferiority margin of −8 points was predefined. Secondary results involved the Foot and Ankle Outcome Score (FAOS), visual analogue scales for pain and function, RAND-36 quality-of-life score, ankle range of motion, fracture union, radiographic congruity, post-traumatic osteoarthritis graded by modified Kellgren-Lawrence scale, and adverse effects. Analyses were conducted mainly on an intention-to-treat basis. Between-group differences in OMAS were analysed by using Student’s t-test with 95% confidence intervals (CIs), and non-inferiority was concluded if the lower bound of the CI was above -8. Sensitivity analyses involved analysis of covariance adjusting for baseline imbalances (age, sex, smoking status, and signs of medial injury. Secondary results were analysed under a superiority framework by using proper parametric or categorical tests. The planned sample size was 126 participants (63 per group), which provide 80% power with α=0.05 and allows for 20% attrition.
Among the 840 patients assessed, 126 were randomised (62 to cast immobilisation and 64 to surgery). A follow-up at 2 years was achieved in 96% of participants. Baseline characteristics were comparable between groups with minor imbalances in smoking status and signs of medical injury. In the primary intention to treat analysis, the mean OMAS at 2 years was 89 in the cast immobilisation group and 87 in the surgery group. The between-group mean difference was 1.3 points (95% CI: -4.8 to 7.3), which exceeded the predefined non-inferiority threshold. This showed that cast immobilization was non-inferior to surgery. Pre-protocol as treated and adjusted analyses yielded consistent results, which reinforce the robustness of primary findings.
No statistically significant differences were observed between groups in any secondary outcomes at 2 years, including FAOS subscales, pain scores, RAND-36 quality-of-life domains, or ankle range of motion. Radiographically, no participant in either group experienced loss of ankle mortise congruency during follow-up. Non-union occurred in one participant per group, and neither required secondary surgery. Most participants in both groups showed no or only mild-to-moderate radiographic signs of post-traumatic osteoarthritis, with no difference in progression between treatments.
Treatment-related adverse events were more common in the surgery group, with complications including superficial wound infections and delayed healing. The cast group experienced rare adverse events, mainly a single non-union. This randomized non-inferiority trial demonstrated that, among patients with isolated Weber B ankle fractures classified as unstable, cast immobilization achieved two-year functional outcomes non-inferior to surgical fixation, with fewer complications. The study supports conservative treatment strategies, which highlight maintenance of congruency with cast immobilization and early weight bearing, and suggest routine surgical fixation may be unnecessary in this fracture subgroup.
Reference: Kortekangas T, Lehtola R, Leskelä H, Taimela S, Ohtonen P, Savola O, et al. Cast immobilisation versus surgery for unstable lateral malleolus fractures (SUPER-FIN): randomized non-inferiority clinical trial. BMJ. 2026;392:e085295. doi:10.1136/bmj-2025-085295
