Background: Ankle contractures are a nearly ubiquitous impairment that develops in individuals with Duchenne muscular dystrophy; however, the underlying tissue changes associated with contracture development are not well understood.
Objective: The goal of this ongoing pilot study is to explore both muscular and Achilles tendon characteristics associated with loss of range of motion to allow for more optimal ankle contracture prevention and management interventions.
Methods: This study is enrolling individuals with DMD and unaffected controls. Active and passive ankle dorsiflexion range of motion is measured in both the knee straight and knee flexed position. All participants undergo an MRI of the lower extremity to determine Achilles tendon length, tendon cross sectional area, and tibial length for normalization. Additionally, muscle fat fraction, an MRI biomarker that estimates the percent of a muscle that has degenerated and been replaced by fat, is being measured in the tibialis anterior, plantarflexors, and thigh extensors using Dixon MRI.
Results: N=8 DMD and N=7 controls have enrolled thus far (Aug ’23-Jan’24). Mean passive ankle dorsiflexion range of motion was 16° in controls, 5° in ambulatory DMD, and -23° in nonambulatory DMD. Normalized Achilles free tendon length was not significantly different between DMD and controls or related to passive ankle dorsiflexion range; however, mid Achilles tendon cross sectional area was significantly smaller in DMD than controls (p<0.0001). Tibialis anterior, plantarflexor, and thigh extensor muscle fat fraction were all correlated with ankle range of motion in DMD (p<0.05), though this analysis is still sample size limited.
Conclusions: A better understanding of the complex interplay between progressive muscle weakness/degeneration and the formation of ankle plantarflexion contractures will allow physicians and physical therapists to make better recommendations for ankle contracture prevention and management. This study will shed light on muscular and tendon factors which may be associated with contracture development.