Background: Practitioners need more sensitive measure to quantify reaching movement for judgment of the treatment effects and reflecting the degrees of motor impairment in upper extremities. The purposes of this study were to identify the specific kinematic characteristics between normal and spastic reaching under different levels of accuracy, and to determine the most sensitive kinematic variable for quantifying the interference of spasticity on reaching.
Methods: Ten normal subjects as control group and ten subjects with spastic cerebral palsy as experimental group were studied. Participants were asked to reach, at a self-selected pace, toward two different sizes of buttons (one with accuracy constraint and the other with non-accuracy constraint) away from normalized distance. Motion analysis system was used to record the trajectory of reaching performance. Kinematic variables of reaching movement were computed and analyzed.
Findings: Measure for movement smoothness presented larger effect size (0.24-0.43) than other kinematic variables adopted in this study. Under high-accuracy reaching, children with spastic cerebral palsy had a prolonged movement time than normal children (P<0.05). Modified Ashworth score was significantly correlated to normalized jerk score, number of movement unit and movement time (r=0.56-0.75). Number of movement unit was the most sensitive kinematic variable to discriminate between normal and spastic reaching.
Interpretation: Development of reliable, valid, and sensitive multi-joint biomechanical evaluation is required, particularly for natural and goal-oriented reaching movement. It is concluded that measure of movement smoothness may be applied as valid and sensitive index to quantify the level of coordinative motor performance for subjects with spastic movement disorder.