A RANDOMISED clinical trial found that cast immobilisation was non-inferior to surgery for unstable ankle fractures, challenging long-standing assumptions about the need for operative management in these injuries.
Ankle fractures are one of the most common fractures amongst adults. Whilst stable fractures can be walked on, unstable fractures require greater support, sometimes requiring surgery. In the recently published SUPER-FIN trial, Kortekangas and colleagues investigate the most effective method of treating unstable ankle fractures.
Unstable Ankle Fractures and the SUPER-FIN Trial
The SUPER-FIN trial was conducted at a specialist university hospital trauma centre in Finland. Kortekangas and colleagues’ objective was to compare cast immobilisation with surgery using open reduction and internal plate fixation for unimalleolar Weber B ankle fractures with a congruent mortise on radiography but deemed unstable by external rotation stress testing.
In the trial, 840 skeletally mature patients, aged 16 and over, diagnosed with an isolated Weber B fibula fracture were assessed for fracture instability by standard external rotation stress test under fluoroscopy. 714 participants were then excluded with stable fractures, mortise incongruency, or fracture dislocation. The 126 remaining participants with a congruent but unstable ankle mortise were then randomly allocated to receive either conventional cast immobilisation for 6 weeks (n=62) or surgical treatment with open reduction and internal plate fixation followed by cast immobilisation for six weeks (n=64).
Cast Immobilisation Outcomes in Unstable Ankle Fractures
The primary outcome measure was the Olerud-Molander Ankle Score (OMAS), ranging from 0–100 points, with higher scores indicating better outcomes and fewer symptoms after 2 years. The trial’s predefined non-inferiority margin for the primary outcome was set at −8 points. Secondary outcomes were pain, ankle function, range of motion, health related quality of life, and radiographic outcome.
121 out of the 126 randomised participants completed the trial. Following the analysis of the 121 participants’ 2 year follow-up, Kortekangas and colleagues calculated the mean OMAS in the cast immobilisation group to be 89, whilst the mean OMAS score for the surgery group was 87 (between group mean difference 1.3 points, 95% confidence interval: −4.8–7.3). No statistically significant difference was observed between the two groups in secondary outcomes. Whilst one participant from each group had radiographic evidence of non-union, one participant in the surgery group had a superficial wound infection. Also in the surgery group, one participant had delayed wound healing, and nine underwent procedures to remove hardware, two of whom developed postoperative infections (one deep, one superficial).
Clinical Implications for Ankle Fracture Management
Considering these results, Kortekangas and colleagues determined that cast immobilisation proved non-inferior to surgery for the treatment of unimalleolar Weber B ankle fractures with a congruent mortise on initial radiography but deemed unstable by external rotation stress testing.
Most significantly, fewer treatment-related harms occurred with cast immobilisation compared to surgery. These insights support a potential shift in attitudes regarding the treatment of unstable fractures and further multicentre studies may help confirm whether these findings should be incorporated into future clinical guidelines.
Reference
Kortekangas et al. Cast immobilisation versus surgery for unstable lateral malleolus fractures (SUPER-FIN): randomised non-inferiority clinical trial. BMJ. 2026; DOI:10.1136/bmj-2025-085295.
