Quantifying passive muscle stiffness in children with and without cerebral palsy using ultrasound shear wave elastography

Aim: The aim of this study was to compare passive muscle stiffness in children with cerebral palsy (CP) and children with typical development using a novel ultrasound technique: ultrasound shear wave elastography (SWE). Method: We conducted a prospective study of 13 children with CP (six females and seven males, median age 5y 1mo [interquartile range 4y 4mo–7y 8mo]) and 13 children with typical development (six females and seven males, median age 5y 3mo [interquartile range 4y 4mo–9y 4mo]). Demographic information and physical exam measurements were obtained in addition to shear modulus measurements (passive muscle stiffness) of the lateral gastrocnemius muscle at 20° plantar flexion, 10° plantar flexion, and 0° plantar flexion using SWE. Results: Children with CP had significantly greater shear modulus measurements at all three foot positions (p<0.050). When the shear modulus values were normalized to the baseline value for each child, there was no significant difference between the two groups. Interpretation: Passive muscle stiffness, measured without the influence of spasticity, is greater in children with CP than in children with typical development when a muscle is at slack and at stretch. When shear modulus was normalized, the results indicate that muscle in children in both groups responds similarly to passive stretch. Further work includes evaluating effect of botulinum toxin on passive muscle properties.