Biometric Characterization of the Stretch Response in Children with Cerebral Palsy and its Relation with the Tardieu Scale

Objective: The main purpose of this study was to determine to what extent resistance to passive stretch, obtained as in the Tardieu test (TS), can evaluate spasticity in the elbow flexors of children with cerebral palsy (CP). Secondary objectives were to evaluate if the TS reflects spasticity severity and if there were any differences in stretch response between the CP group and controls. Methods: Fifteen childrn and adolescents with CP and 15 healthy non-spastic controls were included in the study. All CP participants were affected in the upper extremities, however with different severity of motor impairments. Both groups performed passive elbow extensions at slow and fast velocities, with simultaneous recordings of the Tardieu Scale and biometric (velocity, acceleration and electromyographic activity) measurements. A maximum voluntary isometric contraction was also completed. Results: There was a good agreement (about 65 %) between detected catch with TS (sudden increase in felt resistance) and biometric (EMG burst followed by acceleration change) recordings during the passive elbow extension. However, the passive extension resulted in variable maximum extension velocities in CP participants and at very high velocities a catch was also detected in controls. When high velocity catch was defined as a normal stretch response, the TS overestimated CP participants with abnormal catch in relation to biometrically defined abnormal response. The TS reflected resistance to passive movement in the CP group, but did not separate participants with high muscle activity amplitude from participants with low muscle activity amplitude. Compared to controls, the CP group generally developed higher peak muscle activity in combination with lower maximum extension velocity. However, without knowledge of extension velocity, there was similar muscle activity response in the two groups. Conclusion: In all, resistance to passive stretch, obtained as in the TS, seems to provide a useful evaluation of spasticity in CP children. The results underlines that the TS test protocol should include a maximum extension velocity limit in which a normal stretch reflex does not occur. Further, TS reflect spasticity severity to a limited degree, but resulted in a difference in stretch response in CP and control groups. Keywords: Spasticity, cerebral palsy, Tardieu Scale, biometric measures, electromyograph