Type B ankle fractures with additional medium-sized posterior fragment: mid-term functional and radiological outcome after fixation versus no fixation of the posterior fragment.

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Guidelines for treatment of medium-sized posterior fragments in trimalleolar fractures are scarce and show varying advice. Recent trials comparing fixation and no fixation of posterior fragments, show no difference in outcomes one year postoperatively. This study compares functional outcome and development of osteoarthritis in patients with fixation of a posterior malleolar fracture to patients without fixation of the posterior malleolus fracture. This retrospective cohort study included patients operated for type B ankle fractures with medium-sized (5-25% of joint surface) posterior malleolar fragments in a Dutch level-1 trauma center between 2014 and 2018. ORIF of posterior fragments (FIX) was compared to no fixation (NO-FIX). Choice of treatment was based on the surgeon's preference. Functional outcome was assessed using the AOFAS-score, OMAS-score and VAS-pain. Development of osteoarthritis was assessed on radiographs. A linear regression analysis was performed to identify risk factors for worse functional outcome and osteoarthritis. 27 patients were included in the FIX group and 58 patients in the NO-FIX group. After a median follow-up of 74 months (range 50-108), no difference was observed for functional outcome and pain (median AOFAS 90 vs. 95, OMAS 85 vs. 88, VAS-pain 1 vs. 1; all p > 0.05). Osteoarthritis rates were comparable (grade ≥ 2: 22% in FIX vs. 21% in NO-FIX, p = 0.87). Median fragment size was 15.7% versus 13.6% of the tibial articular surface after FIX and NO-FIX respectively. Median postoperative step-off on radiograph was 0.0mm after FIX and 0.8mm after NO-FIX (p = 0.20). Complication rates, including infection, secondary operation and hardware removal, were comparable. Postoperative step-off > 1mm increased the risk of osteoarthritis (odds ratio 3.9, 95% CI 1.2-12.7). The value of fixation of medium-sized posterior fragments in type B ankle fractures seems limited after mid-term follow-up, although functional impairment caused by osteoarthritis might develop in the long-term. Because postoperative step-off > 1mm increases the risk of osteoarthritis, restoration of the tibial plafond seems essential.