Three week versus six week immobilisation for stable Weber B type ankle fractures: randomised, multicentre, non-inferiority clinical trial

Abstract

Objective: To determine whether treatment of isolated stable Weber B type ankle fractures with a cast or a simple orthotic device for three weeks produces non-inferior outcomes compared with conventional immobilisation in a cast for six weeks.

Design: Randomised, pragmatic, non-inferiority, clinical trial with blinded outcome assessment.

Setting: Two major trauma centres in Finland, 22 December 2012 to 6 June 2016.

Participants: 247 skeletally mature patients aged 16 years or older with an isolated Weber B type fibula fracture and congruent ankle mortise in static ankle radiographs.

Interventions: Participants were randomly allocated to conventional six week cast immobilisation (n=84) or three week treatment either in a cast (n=83) or in a simple orthosis (n=80).

Main outcome measures: The primary, non-inferiority, intention-to-treat outcome was the Olerud-Molander Ankle Score at 12 months (OMAS; range 0-100; higher scores indicate better outcomes and fewer symptoms). The predefined non-inferiority margin for the primary outcome was -8.8 points. Secondary outcomes were ankle function, pain, quality of life, ankle motion, and radiographic outcome. Follow-up assessments were performed at 6, 12, and 52 weeks.

Results: 212 of 247 randomised participants (86%) completed the study. At 52 weeks, the mean OMAS was 87.6 (SD 18.3) in the six week cast group, 91.7 (SD 12.9) in the three week cast group, and 89.8 (SD 18.4) in the three week orthosis group. The between group difference at 52 weeks for the three week cast versus six week cast was 3.6 points (95% confidence interval -1.9 to 9.1, P=0.20), and for the three week orthosis versus six week cast was 1.7 points (-4.0 to 7.3, P=0.56). In both comparisons, the confidence intervals did not include the predefined inferiority margin of -8.8 points. The only statistically significant between group differences observed in the secondary outcomes and harms in the two primary comparisons were slight improvement in ankle plantar flexion and incidence of deep vein thrombosis, both in the three week orthosis group versus six week cast group.

Conclusion: Immobilisation for three weeks with a cast or orthosis was non-inferior to conventional cast immobilisation for six weeks in the treatment of an isolated stable Weber B type fracture.

Trial registration: ClinicalTrials.gov NCT01758835.

Fig 1

Weber classification for lateral malleolar (fibula) fractures. Type A: Fracture below level of ankle joint. Type B: Fracture starts distally at level of ankle joint (syndesmosis) and extends proximally. Type C: Fracture proximal to syndesmosis (level of ankle joint)

Fig 2

Trial profile

Fig 3

Presentation and interpretation of primary outcome Olerud-Molander Ankle Score (OMAS) at 52 weeks using confidence intervals in relation to non-inferiority margin. Given that confidence intervals for both comparisons (three week orthosis versus six week cast and three week cast versus six week cast) lie to the right of the non-inferiority margin (∆, −8.8 points) and also include zero, the interpretation is: new treatments (three week orthosis and cast) are non-inferior to the control (six week cast) but not shown to be superior. Error bars indicate two sided 95% confidence intervals. Dashed line indicates non-inferiority margin; shaded region indicates zone of non-inferiority

Fig 4

Trajectories of treatment responses for primary outcome in three study groups over course of trial. Circles represent mean values of each group at each follow-up point. Bars indicate standard deviations. OMAS=Olerud-Molander Ankle Score