Longitudinal ankle range of motion and functional decline in Duchenne muscular dystrophy

Contractures limit movement in Duchenne muscular dystrophy (DMD). Ankle contractures due to gastrocnemius (GNM) and/or soleus muscles (SM) shortening are common but the effect of GNM and SM contractures on physical functioning and whether asymmetry (difference left and right) has impact remain unclear.Data from 129 ambulant DMD patients with 496 visits (median 4 visits/patient (IQR:2-5), median baseline age 6.1 (IQR:5.5-8.6)) were used to address this knowledge gap.Ankle dorsiflexion (AD) was measured with knee in extension (GNM) and flexion (SM). Associations between AD-GNM, AD-SM and North Star Ambulatory Assessment (NSAA), 10-meter walk/run velocity (10MWTv), 6-minute walk test(6MWT), 4-stairs climb velocity(4SCv) as well as influence of asymmetry were analysed using linear mixed models.A 5° AD-GNM decline was associated with a decrease in NSAA-score (β-estimate: -1.51, p < 0.001) and 10MWTv (β-estimate: -0.10m/s p < 0.05). A 5° decline in AD-SM was associated with a decrease in 10MWTv (β-estimate: -0.09 m/s, p < 0.05). For the 6MWT, 5° AD-GNM was associated with 11.3 m decrease (p < 0.05) and 5° asymmetry with an additional 15.8 m decrease (p = 0.05).Both GNM and SM shortening were associated with functional decline in DMD, asymmetry seemed to contribute to additional decline. This study highlights the relevance of contracture management targeting both GNM, SM and asymmetry.