Kinematics of the Shoulder Girdle During Pointing: Coordination Between Joints and their Contribution to the Peri-Personal Workspace.

This study explored the coordination between the components of the shoulder girdle (clavicle, scapula and humerus), and how they contribute to hand movement in the peri-personal space. Shoulder girdle motion was recorded in 10 healthy subjects during pointing movements to 9 targets in the peri-personal space, using electromagnetic sensors fixed to the trunk, scapula and upper arm. Most of the 9 degrees of freedom (DoF) of the shoulder girdle were finely scaled to target position. Principle component analysis revealed that the 6 DoF of scapula-thoracic motion were coordinated in three elementary patterns (protraction, shrug and lateral rotation). The ratio of gleno-humeral to scapulo-thoracic global motion was close to 2:1. A direct kinematic procedure showed that if no scapular motion occurred, the workspace would be reduced by 15.8 cm laterally, 13.7 cm vertically and 4.8 cm anteriorly. Scapulo-thoracic motion should be taken into account when investigating the physiology of upper-limb movements. [ABSTRACT FROM AUTHOR]