Surgery versus non-operative treatment for ER-stress unstable Weber-B unimalleolar fractures: a study protocol for a prospective randomized non-inferiority (Super-Fin) trial

Roughly two-thirds of ankle fractures are unimalleolar injuries, the Weber B-type fibula fracture being by far the most common type. Depending on the trauma and the accompanying soft-tissue injury, these fractures are either stable or unstable. Current clinical practice guidelines recommend surgical treatment for unstable Weber B-type fibula fractures. An ongoing randomized, parallel group, non-inferiority trial comparing surgery and non-operative treatment for unstable Weber B-type ankle fractures with allocation ratio 1:1. The rationale for non-inferiority design is as follows: By being able to prove non-inferiority of non-operative treatment, we would be able to avoid complications related to surgery. However, the primary concern related to non-operative treatment is increased risks of ankle mortise incongruency, leading to secondary surgery, early post-traumatic osteoarthritis and poor function. After providing informed consent, 126 patients aged 16 years or older with an unimalleolar Weber B-type unstable fibula fracture were randomly assigned to surgery (open reduction and internal fixation) or non-operative treatment (6-week cast immobilization). We have completed the patient enrolment and are currently in the final stages of the 2-year follow-up. The primary, non-inferiority outcome is the Olerud-Molander Ankle Score (OMAS) at 2 years (primary time point). The predefined non-inferiority margin is set at 8 OMAS points. Secondary outcomes include the Foot and Ankle Score, a 100 mm Visual Analogue Scale for function and pain, the RAND-36-Item Health Survey for health-related quality-of-life, the range-of-motion of the injured ankle, malunion (ankle joint incongruity) and fracture union. Treatment-related complications and harms; symptomatic non-unions, loss of congruity of the ankle joint, reoperations and wound infections will also be recorded. We hypothesize that non-operative treatment yields non-inferior functional outcome to surgery, the current standard treatment, with no increased risk of harms.