Muscle hypoextensibility in children with cerebral palsy: I. Clinical and experimental observations.
Extensibility of the triceps surae was compared in 12 normal children and in 21 children with cerebral palsy (CP). The latter group represented selected subjects who showed hypoextensibility in ischemia-tested noncontracting muscle, which is considered an indication of change in the physical properties of muscle. The difference between the 2 groups is illustrated by curves plotting torque of the noncontracting muscle against tibiocalcanean angles. Two measurements were found to be especially representative: 1) the angle related to a very slight torque and 2) the angle corresponding to a strong, standardized torque. In children with CP and with muscle hypoextensibility, both angles had abnormally high values and the difference between the 2 measurements was abnormally small. These findings indicate an insufficient range of passive muscle stretch, reflected by excessive steepness of the torque-angle curve. In normal children, maximal muscle contraction produces full plantar flexion; in some children with CP, contraction fails to produce any force in full plantar flexion. Instead, force is generated only at a smaller tibiocalcanean angle when the muscle reaches a sufficient length. These cases represent hypoextensibility with abnormally short muscle and abnormally long tendon. Data obtained by instrumental measurements can be reproduced with sufficient accuracy by appropriate clinical technique as described in this paper, and applied clinically, as described subsequently.