Cast also carries fewer treatment related harms than surgery, say researchers
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, finds a clinical trial from Finland published by The BMJ today.
Around 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.
To explore this further, 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 between January 2013 and 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.
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 8 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).
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.
The 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]," they 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."
This team is to be commended for conducting a robust study which addresses an important clinical question, and will support treatment decisions and updates to clinical guidelines, say UK researchers in a linked editorial.
They discuss some limitations, but say 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."
