INTERJOINT COORDINATION DURING POINTING MOVEMENTS IS DISRUPTED IN SPASTIC HEMIPARESIS

Approaches to the rehabilitation of movement in spastic hemiparetic pa tients depend on knowledge of the underlying mechanisms of movement de ficits. The goals of this study were to characterize end-point traject ories and interjoint coordination of arm pointing movements to differe nt targets on a horizontal planar surface and to correlate disruptions in motor control in the affected arm of hemiparetic subjects with the level of spasticity and the degree of functional impairment measured clinically. Arm movements were studied in six normal and 10 hemipareti c subjects. Data from the affected alms of hemiparetic subjects were c ompared with those from their non-affected arms and to data from the a rms of normal subjects. Subjects were seated in front of a horizontal surface adjusted to the height of the sternal notch with the trunk sta bilized. They made planar arm reaching movements (20 and 40 cm) to fou r different targets located directly in front of them and in the ipsil ateral and contralateral workspace. Kinematic data from the finger wri st, elbow and shoulder were recorded with a three-dimensional optical tracking system. Results showed that movement amplitudes were lower an d movement times were significantly prolonged in the affected arms. Al though trajectories were marked by deviations from smooth straight lin es and characterized by increased dispersion and segmentation, even th ose subjects with the most severe spasticity could reach into all part s of the workspace with both their affected and non-affected arms. Thi s indicated that movement planning in terms of extrapersonal space was unaffected in these subjects. On the other hand, the interjoint coord ination of movements made into or out of the typical extensor or flexo r synergies was equally disrupted These findings suggest a bi-level co ntrol organization of pointing movements in both normal and hemipareti c subjects: the level of trajectory planning in extrapersonal space an d the level specifying interjoint coordination according to the trajec tory plan. Deficits in motor performance in stroke patients may be ass ociated with problems at the second control level. This implies some s trategies for the rehabilitation of stroke patients with motor disorde rs. Treatment aimed at improving arm function should be oriented towar d restoring the normal sensorimotor relationships between the joints. We also found that while clinical spasticity scores were correlated wi th some aspects of motor performance, they provided little information about the movement deficit itself.