Co-contraction during passive movements of the knee joint in children with cerebral palsy

BACKGROUND: Co-contraction is an impairment commonly reported in children with cerebral palsy. However, co-contraction has not been investigated during passive movements which may be used to assess spasticity in children with cerebral palsy. The purpose of this study was to examine the frequency of co-contraction and the relationship between reflex activity and co-contraction during passive movements of the knee joint in children with cerebral palsy. METHODS: Twenty children with cerebral palsy participated in this study. One set of ten continuous passive movements from 90 degrees of knee flexion to 25 degrees of knee flexion and from 25 degrees of knee flexion to 90 degrees of knee flexion was completed at 15 degrees /s, 90 degrees /s, and 180 degrees /s. The mean percentage of the range of motion of each movement and mean percentage of the number of movements which exhibited electromyographic activity of the vastus lateralis, medial hamstrings, and co-contraction were calculated for each set of movements. FINDINGS: The number of the movement repetitions and the percentage of the range of motion which exhibited co-contraction were considerable regardless of the direction and speed of motion. Significant positive correlations were found between the percentage of the passive range of motion with medial hamstrings activation, vastus lateralis activation, and co-contraction during passive movements into both knee flexion and knee extension at a velocity of 15 degrees /s, 90 degrees /s, and 180 degrees /s (P<0.001). INTERPRETATION: Co-contraction commonly occurs during passive movements of the knee in children with cerebral palsy. The presence of co-contraction may influence measurements of spasticity which use passive movements to assess spasticity.