Relation between spasticity and strength in individuals with spastic diplegic cerebral palsy

The relation between spasticity and strength in individuals with cerebral palsy (CP) has not been extensively researched. Knee and ankle spasticity and strength were quantified in a retrospective analysis of 60 individuals with spastic diplegic CP (mean age 12 years, range 3 to 38) and a group of 50 individuals without disabilities (WD group; mean age 12 years, range 4 to 36). Spasticity was measured using a KinCom dynamometer that stretched the passive knee flexors or ankle plantarflexors at different speeds and recorded the amount of resistive torques. For the strength tests, the participant performed a maximum contraction of the knee flexors/extensors and ankle plantarflexors/dorsiflexors throughout their range of motion at a speed of 10 degrees/s on the dynamometer. Pearson's correlation coefficient was used to determine if a relation existed between spasticity and strength within the same muscle group and in opposing muscle groups at the knee and ankle joints. A t-test was performed to determine if greater spasticity and less strength existed at the ankles compared with the knees in those with CP. Results show that there was no relation between spasticity and strength either within the same muscle group or at opposing muscle groups at the knee and ankle joints in persons with CP. Individuals with spastic diplegic CP were more involved (greater spasticity, less strength) distally at the ankles compared with the knees. The findings conflict with the literature, which contains several assumptions, one of which is that a spastic muscle is a strong muscle and that spasticity causes weakness in the opposing muscle group. We found no relation between spasticity and strength in individuals with CP. Our findings support the literature, which states that individuals with spastic diplegic CP are more involved distally compared with proximally in the lower extremities.