Kinematics of prehension and pointing movements in C6 quadriplegic patients

Aims: C6 quadriplegic patients lack voluntary control of their triceps musc le but can still perform reaching movements to grasp objects or point to ta rgets. The present study documents the kinematic properties of reaching in these patients. Materials and methods: We investigated the kinematics of prehension and poi nting movements in four quadriplegic patients and five control subjects. Pr ehension and pointing movements were recorded for each subject using variou s object positions (ie different directions and distances from the subject) . The 3D motion was analyzed with Fastrack Polhemus sensors. Results: During prehension tasks the velocity profile of control subjects s howed two peaks (go and return); the first velocity peak was scaled to the distance of the object. In quadriplegic patients there was a third intermed iary peak corresponding to the grasping of the object. The amplitude of the first peak was slightly smaller than in control subjects. Velocity was sca led to the distance of the object, but with a greater dispersion than in co ntrol subjects. Total movement time was longer in quadriplegics because of the prolonged grasping phase. There were few differences in the pointing mo vements of normal and quadriplegic subjects. The scapula contributed more t o the reaching phase of both movements in quadriplegic patients. Conclusion: In spite of some quantitative differences, the kinematics of th e hand during reaching and pointing in quadriplegic patients are surprising ly similar to those of control subjects.