Cast immobilization is non-inferior to surgical intervention in isolated Weber B fractures of lateral malleolus

1. Cast immobilization is non-inferior to surgical treatment with open reduction and internal plate fixation (ORIF) in the management of isolated Weber B fractures of the lateral malleolus with a congruent mortise on initial radiographs but deemed unstable on external rotation stress testing.

Evidence Rating Level: 1 (Excellent)

Management of isolated Weber B fractures of the lateral malleolus depends on ankle mortise congruency. While these fractures are managed with cast immobilization, some patients develop occult incongruency. Formalised stress testing under fluoroscopy has been introduced to better assess stability. However, it is unclear if surgery or cast immobilization is better in patients with radiographically congruent Weber B fractures classified as unstable by external rotation testing. This randomized, parallel-group, non-inferiority trial included 124 patients. 61 (mean [SD] age, 46 [18] years; 44% female) were randomized to cast immobilization for 6 weeks and 63 (mean [SD] age, 43 [19] years; 40% female) were randomized to surgical treatment with ORIF followed by cast immobilisation for six weeks. The primary, non-inferiority outcome was the Olerud-Molander Ankle Score (OMAS; range 0-100 points; higher scores indicating better outcomes and fewer symptoms) at two years. After 2 years, the mean OMAS at two years was 89 in the cast immobilisation group and 87 in the surgery group (between-group mean difference 1.3 points, 95% CI −4.8 to 7.3). There were no significant differences in the Foot and Ankle Outcome Score or RAND-36 health survey. No participant in either group experienced a loss of congruence. Adverse events in the surgery group included superficial wound infection (n=1 participant), delayed wound healing (n=1), and hardware removal procedures (n=9). At two years, cast immobilization was non-inferior and had fewer complications compared to surgery for management of isolated Weber B ankle fractures with a congruent mortise on initial radiographs but deemed unstable on external rotation stress testing. 

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