To date, clinical tests are unable to differentiate between the cause of muscle stiffness, although a manual instrumented spasticity assessment for the lower limb that utilizes surface electromyogram has recently been proposed. This study intends to use shear wave elastography to assess individual muscle stiffness parameters and the individual response to botulinum toxin injection in the elbow and wrist flexors. Collection of baseline spasticity parameters could then be used to predict the effect of botulinum toxin type A and ultimately serve as a basis for development of a treatment model for muscle spasticity in patients with spastic cerebral palsy.