A new study suggests that six weeks in a cast is no less effective than surgery for an unstable ankle fracture.
In fact, researchers noted that a cast also carries fewer treatment-related harms than surgery.
The clinical trial from Finland, published in The BMJ, found that 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.
Around two-thirds of all ankle fractures involve a break in the fibula – these Weber B fractures leave the ankle either stable or unstable.
Surgery remains the main treatment for unstable Weber B ankle fractures, despite recent trials and guidelines increasingly supporting non-surgical options in selected patients.
To explore this further, researchers assessed whether cast immobilisation is comparable to surgery in adults with unstable Weber B ankle fractures.
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) to assess healing.
An eight-point difference between groups was predefined 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 observed in any of the other outcomes, and overall, fewer treatment-related harms occurred with cast immobilisation than with surgery.
The authors acknowledge that their trial was conducted at a single university hospital, which may limit generalisability, and note the lack of consensus on the external rotation stress test for determining fracture instability.
However, they add that this was a robust analysis with a high two-year follow-up rate – a time point generally considered sufficient to capture longer-term outcomes.
In the paper, they noted: ‘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. 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.’
UK researchers, in a linked editorial, said the team deserved commendation for conducting a robust study that addresses an important clinical question and will support treatment decisions and updates to clinical guidelines.
