Electromyographic test to differentiate mild diplegic cerebral palsy and idiopathic toe-walking.

The purpose of this study was to determine whether children with mild spastic diplegic cerebral palsy (CP) could be differentiated from those with idiopathic toe-walking (ITW) based on an obligatory coactivation during voluntary contraction of the quadriceps or gastrocnemius. Twenty-four subjects participated in this study, eight children with mild spastic diplegia CP, eight with ITW, and eight age-matched controls. Measurements included passive range of motion and surface electromyographic recordings of the lateral quadriceps and lateral gastrocnemius. Electromyographic recordings were obtained during resisted knee extension with knee flexed 30 degrees, isometric quadriceps contraction with knee extended (quad set), active plantarflexion, and during gait. The range-of-motion values were not different between the CP and ITW subjects, with the exception of the popliteal angle, which was greater in subjects with CP, with an overlap in values. Gait electromyography showed premature firing of gastrocnemius in swing in both groups of subjects compared with controls. During resisted knee extension and quad set, the mean duration of gastrocnemius coactivation in subjects with CP was high: 86% and 86% compared with 20% and 35% for the subjects with ITW and 0.4% and 3% for controls, respectively. Voluntary plantarflexion did not consistently elicit coactivation of the quadriceps. The results suggest that electromyographic testing of resisted knee extension and quad set to identify gastrocnemius coactivation can help differentiate patients with mild CP from those with ITW.