Comparison of muscle strength and in-vivo muscle morphology in young children with haemophilia and those of age-matched peers.

Recent advances in imaging have enhanced our understanding of the morphological adaptations of muscle in response to disease and altered use. Adaptation in muscle morphology has been linked to changes in muscle strength. To date, no studies have compared muscle morphology and strength in young children with haemophilia to that of typically developing children. This study explored differences in muscle strength and morphology between typically developing and age and size-matched boys aged 6-12 years with haemophilia and a history of recurrent haemorrhage in the ankle joint. Maximum muscle strength of the knee flexors (KF), extensors (KE), ankle dorsi (ADF) and plantar flexors (APF) was measured in 19 typically developing boys (Group 1) and 19 boys with haemophilia (Group 2). Ultrasound images of vastus lateralis (VL) and lateral gastrocnemius (LG) were recorded to determine muscle cross-sectional area (CSA), thickness, width, fascicle length and pennation angle. Muscle strength of the KE, ADF and APF were significantly (P < 0.05) lower in Group 2 when compared with Group 1. Muscle CSA and width of VL were significantly smaller and pennation angles significantly larger in Group 2 (P < 0.05). Muscle CSA and thickness of LG were significantly (P < 0.05) smaller in Group 2. Linear regression showed that LG muscle CSA and thickness were significant (P < 0.01) predictors of APF muscle strength. Following ankle joint bleeding in young boys with haemophilia, secondary adaptations in muscle strength and morphology were observed, suggesting that muscle function is more impaired than current clinical evaluations imply.