Shoulder movements during quadrupedal locomotion in arboreal primates

The kinematics of scapula and shoulder joint movements were analyzed in three species of arboreal quadrupedal primates using cineradiography. Our findings indicate that scapular movement is highly important for forelimb movement in primates with this ancestral mode of locomotion. Retroversion of the scapula (syn. caudal rotation or extension) during the stance phase contributes more than 40% to the stride length of the forelimb. Lateral forelimb excursions, a general feature for arboreal primates, are based on complex three-dimensional scapular movements guided by the clavicle. Humeral abduction is achieved by scapular abduction and transversal rotation of the scapula about its longitudinal axis, and is therefore strikingly different from humeral abduction in humans. At the same time, the movements of the shoulder joint are limited to flexion and extension only.