Coordination between reaching and grasping in adults with hemiparesis

Kinematics and control deficits of altered prehension in patients with upper limb motor deficits due to stroke have not been well-described. A previous study showed that patients with mild to moderate arm motor impairment used similar grip apertures as healthy subjects when grasping a 35 mm diameter cylinder with the whole hand. However, other characteristics of reaching and grasping related to motor coordination and control have not been described. We studied the coordination between reaching and grasping as well as the characteristics of grasping in subjects with hand motor deficits and healthy control subjects when reaching to grasp objects of two different sizes using two types of grasping. Twelve patients with chronic hemiparesis and 7 neurological healthy subjects participated. Patients had sustained a stroke 17?12 mos previously and had mild to moderate hand paresis (Fugl-Meyer Hand Scores 10-23/24). Subjects reached and grasped cylindrical objects of small (33mm) and large (55mm) diameter with the whole hand or with the fingertips (10 trials each). Twelve infrared emitting diodes were placed on bony landmarks of the hand, arm and trunk and kinematic data were recorded by an optical analysis system (Optotrak) at 120 Hz. In both groups, grip aperture sizes varied with cylinder diameter (p<0.001) and the type of grasping or object size had no effect on temporal parameters of reaching. However, during reaching, patients with hemiparesis had longer movement times (p<0.001) and prolonged durations of the deceleration phase of reaching compared to the healthy group (p<0.001). In contrast, during the prehension phase, both the size of the object and the type of grasping affected the temporal parameters of grasping. In both groups, the relative time to maximal aperture of the hand occurred earlier when stroke participants grasped the small object with the whole hand. Subjects with stroke also took longer to open the hand for all grasping conditions. Three patients had complete disruption in coordination between reaching and grasping. In the remaining 9 patients and in the healthy subjects, the relative delay between the time to peak arm velocity and the time to maximal hand aperture was similar. Patients with different degrees of hand paresis retained the ability to scale grip aperture to cylinder size independently of grasp type but may have disruptions in the coordination between reaching and grasping.