Medial Malleolus: Operative Or Non-operative (MOON): A randomised clinical trial of operative versus non-operative management of associated medial malleolus fractures in unstable ankle fractures

T. Carter, W. Oliver, K. Bell, C. Graham, A.D. Duckworth, T. White, N. Heinz

¹Edinburgh Orthopaedic Trauma, Royal Infirmary of Edinburgh, Edinburgh, United Kingdom

²Edinburgh Clinical Research Facility, Edinburgh, United Kingdom

³University of Edinburgh, Centre for Population Health Sciences, Edinburgh, United Kingdom

Winner of the BOFAS 2024 Third Trainee Prize (Podium)

Introduction: Unstable ankle fractures are routinely managed operatively. Due to soft-tissue and implant related complications, there has been recent literature reporting on the non-operative management of well-reduced medial malleolus fractures following fibular stabilisation, but with limited evidence supporting routine application. This trial assessed the superiority of internal fixation of well-reduced (displacement ≤2mm) medial malleolus fractures compared with non-fixation following fibular stabilisation.

Methods & Participants: Superiority, pragmatic, parallel, prospective randomised clinical trial conducted over a four year period. A total of 154 adult patients with a bi- or trimalleolar fractures were recruited from a single centre. Open injuries and vertical medial malleolar fractures were excluded. Following fibular stabilisation, patients were randomised intra-operatively on a 1:1 basis to fixation or non-fixation after satisfactory fluoroscopic fracture reduction was confirmed. The primary outcome was the Olerud Molander Ankle Score (OMAS) at one-year post-randomisation. Complications and radiographic outcomes were documented over the follow-up period.

Results: Among 154 participants (mean age, 56.5 years; 119 women [77%]), 144 [94%] completed the trial. At oneyear the median OMAS was 80 (IQR, 60-90) in the fixation group compared with 72.5 (IQR, 55-90) in the non-fixation group (p=0.17). Complication rates were comparable. Significantly more patients in the non-fixation group developed a radiographic non-union (20% vs 0%; p<0.001), with the majority (n=8/13) clinically asymptomatic and one patient required surgical re-intervention for this. Fracture type and reduction quality appeared to influence fracture union and patient outcome.

Conclusion: In this randomised clinical trial comparing internal fixation of well-reduced medial malleolus fractures with non-fixation, following fibular stabilisation, fixation was not superior according to the primary outcome. However, 1 in 5 patients following non-fixation developed a radiographic non-union and whilst the re-intervention rate to manage this was low, the future implications require surveillance. These results may support selective non-fixation of anatomically reduced medial malleolus fractures.

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