Wearing a cast for six weeks appears to be no less effective than surgery for healing unstable ankle fractures and carries fewer treatment-related harms, according to the results of a clinical trial conducted in Finland.
Published today (14 January) in The BMJ today, the article suggests that about two thirds of all ankle fractures involve a break in the fibula (the outer ankle bone). Known as Weber B fractures, they leave the ankle either stable or unstable (at risk of falling out of alignment).
Surgery remains the main treatment for Weber B ankle fractures deemed unstable, despite recent trials and guidelines increasingly supporting non-surgical options in selected patients.
The first author is Tero Kortekangas, who is based at the Department of Orthopaedics and Traumatology at Oulu University Hospital. Dr Kortekangas and his fellow researchers set out to assess whether cast immobilisation is comparable (‘non-inferior’) to surgery in adults with Weber B ankle fractures deemed unstable.
They identified 126 participants aged 16 years or older with an unstable Weber B ankle fracture confirmed by an external rotation stress test at a specialist university hospital trauma centre in Finland from January 2013 to July 2021.
Sixty-two participants were randomly assigned to conventional cast immobilisation for six weeks and 64 were assigned to undergo surgery followed by cast immobilisation for six weeks.
Physiotherapists guided rehabilitation
Both groups had check-ups at two, six and 12 weeks and met with a physiotherapist at six and 12 weeks to guide rehabilitation.
At two years, participants were assessed using the Olerud-Molander Ankle Score (OMAS), a 0-to-100-point scale where higher scores indicate better healing. An eight-point difference between groups was pre-set as the non-inferiority margin.
Other check-up assessments included ankle function, pain, health related quality of life, ankle range of motion and X-rays. Treatment related adverse events were also recorded.
In all, 121 of the 126 randomised participants completed the two-year follow-up. The mean OMAS was 89 in the cast immobilisation group and 87 in the surgery group (a between group mean difference of 1.3 points).
‘Our findings and those of previous studies show that a standard below-the-knee cast provides adequate stabilisation of an isolated unimalleolar fibular fracture with a congruent ankle mortise’ [Tero Kortekangas et al]
No statistically significant between group differences were seen in any of the other outcomes and overall, fewer treatment related harms occurred with cast immobilisation compared with surgery.
Caveats and conclusions
Dr Kortekangas and his fellow authors acknowledge that their trial was from a single university hospital, which may limit generalisability and note the lack of consensus of the external rotation stress test to determine fracture instability, but say this was a robust analysis that achieved a high follow-up rate at two years – a time point generally considered sufficient to capture longer term outcomes.
‘Together, our findings and those of previous studies show that a standard below-the-knee cast provides adequate stabilisation of an isolated unimalleolar fibular fracture with a congruent ankle mortise [the bracket-shaped socket of the ankle],’ Dr Kortekangas and his fellow researchers write.
‘This lends further support to the evolving concept that the treatment of ankle fractures should focus on obtaining and maintaining a congruent ankle mortise until fracture union, using the most conservative means possible.’
Study is robust, say UK-based clinicians
This team should be commended for conducting a robust study which addresses an important clinical question, and will support treatment decisions and updates to clinical guidelines, say David J Keene and Matthew L Costa in a linked editorial.
They are based at Oxford Trauma and Emergency Care, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford.
While the authors discuss some limitations, they say that, collectively, this and other trials ‘are supporting much needed advances in the evidence base for ankle fracture management and are a testament to the collaborative network of trauma and orthopaedic health professionals, researchers, and, most importantly, patient participants’.
To access the research study – titledCast immobilisation versus surgery for unstable lateral malleolus fractures (SUPER-FIN): randomised non-inferiority clinical trial doi: 10.1136/bmj-2025-085295 – click
To access the editorial– titled A step forward for ankle fracture management doi: 10.1136/bmj.s56 – click
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