The perception of limb position in space and during passive and active limb movement is referred to as proprioception. Patients with pathological shoulder patterns have either motor deficiencies, an "impaired" position sense, proprioceptive deficits or a combination of these factors. Consequently, an objective evaluation of the patients' proprioceptive abilities is increasingly necessary for the planning of successful rehabilitation programmes.
To objectively describe the connection between arm proprioception and visual feedback, the relationship between unconstrained arm movement and eye movement is being investigated. The motion analysis laboratory at the Helmholtz Institute provides contact-free recording of unconstrained body movements with high spatial and temporal resolution (c.f. Fig .1). The motion analysis system records the trajectories of passive reflecting markers attached to the limbs using infrared cameras. By means of an eye-tracker system, it is possible to specify the direction of gaze of patients during unconstrained head movements. In order to investigate complex, yet exactly reproducible movement sequences of the upper extremity, a robot with a motor-operated ‚hand' was incorporated into the system. The robot gives various 3-D paths of a target for tracking by the subjects.
The data collected is analysed using a suitable kinematic model. The results of a tracking test in which a triangular path was presented is shown in Fig. 2. During this movement the path of the object was closely followed by the eyes and finger. This confirms that subjects with healthy shoulders are able to successfully combine visual and proprioceptive information.
In the case of patients with limited proprioceptive abilities, it is expected that such a graphical representation will show increased course deviations. The direction of gaze will be focused more upon the finger and less upon the object. In doing so, the weaker joint position sense is supported.