Regulation of stretch reflex threshold in elbow flexors in children with cerebral palsy: a new measure of spasticity

The tonic stretch reflex threshold in children with cerebral palsy (CP) was measured to determine its test-retest reliability and its concurrent valid ity as a potential measure of spasticity. Fourteen children with spastic CP aged 6 to 18 sears were tested on three separate occasions for clinical sp asticity and stretch reflex thresholds of affected elbow flexors. Electromy ographic (EMG) recordings were obtained by surface electrodes for elbow fle xors and extensors during mechanical displacements of the passive joint tow ards extension. Displacements were produced by a torque motor at seven velo cities which randomly varied from trial to trial. EMG activity was measured in the stretched flexor muscles to determine threshold angles and velociti es for each velocity of stretch. These were plotted on a velocity-angle-pha se diagram and regression analysis was used to determine the static stretch reflex threshold for each participant. The measure showed good test-retest reliability for the group (ICC 0.73, p < 0.001) whereas a significant corr elation between the measure and the clinical spasticity scale was not found . This technique is a potential outcome variable for measuring the efficacy of treatments aimed at decreasing spasticity in children with CP.