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

Only 26 children were analysed, and the authors used non-parametric tests because of the limited sample size, so null findings for associations may reflect limited numbers. Children with GMFCS levels IV and V were difficult to recruit, and all children with CP had some ambulatory ability, so results may not apply to more impaired children. Only the lateral gastrocnemius was measured, so stiffness in other muscles or joints is unknown. Ankle range of motion was measured with a goniometer, which the authors note has 5° to 14° variability in children with CP. Previous botulinum toxin injections were recorded only as presence and timing, not number or dose, so injection effects cannot be interpreted. Shear modulus conversion assumes muscle behaves like a simple elastic material, which it does not. The sex difference at 10° plantarflexion was found in a small subgroup, and the authors say its relevance is uncertain.

Do not read shear modulus as a spasticity score or a guide to botulinum toxin treatment. It did not correlate with Modified Ashworth Scale, GMFCS level, or botulinum toxin history, and the study was small and measured only one muscle.