Orientation of the scapula in a simulated wheelchair push.

For a systematic study of the efficiency of manual wheelchair propulsion, biomechanical and functional analysis of the wheelchair push is necessary. Recently a three-dimensional (simulation) model of the shoulder mechanism has been developed. For a complete analysis with this model, information on force and kinematics is needed. To determine the three-dimensional orientations of the scapula during wheelchair propulsion static measurements in different phases of the push (-15, 0, 15, 30, and 60) relative to the vertical through the wheel axis) and against different loads (0, 10, 20, 30 and 40% of the maximal torque) have been performed. Scapular rotations were generally small and correlated poorly with net torque on the glenohumeral joint. On the basis of the measurements of thoracal and humeral orientation and net torque, equations have been formulated which can be used to describe the scapular orientation during actual wheelchair propulsion. Its consequences and applicability are discussed.