Statistical Models to Assess Leg Muscle Mass in Ambulatory Children With Spastic Cerebral Palsy Using Dual-Energy X-Ray Absorptiometry

Cerebral palsy (CP) is a movement disorder associated with small and weak muscles. Methods that accurately assess muscle mass in children with CP are scarce. The purpose of this study was to determine whether dual-energy X-ray absorptiometry (DXA) accurately estimates midleg muscle mass in ambulatory children with spastic CP. Ambulatory children with spastic CP and typically developing children 5-11 y were studied (n = 15/group). Fat-free soft tissue mass (FFST) and fat mass at the middle third of the tibia (i.e., midleg) were estimated using DXA. Muscle mass (muscle_MRI) and muscle mass corrected for intramuscular fat (muscle_MRIfc) in the midleg were estimated using magnetic resonance imaging (MRI). Statistical models were created to predict muscle_MRI and muscle_MRIfc using DXA. Children with CP compared to typically developing children had lower FFST (38%), muscle_MRI (40%) and muscle_MRIfc (47%) (all p < 0.05) and a lower ratio of muscle_MRIfc to FFST (17%, p < 0.05). DXA-based models developed using data from typically developing children overestimated muscle_MRI (13%) and muscle_MRIfc (22%) (both p < 0.05) in children with CP. DXA-based models developed using data from children with CP explained 91% of the variance in muscle_MRI and 90% of the variance in muscle_MRIfc in children with CP (both p < 0.05). Moreover, the estimates were not different from muscle_MRI and muscle_MRIfc (both p > 0.99). We conclude that DXA-based statistical models accurately estimate midleg muscle mass in children with CP when the models are composed using data from children with CP rather than typically developing children.