3-DIMENSIONAL RECORDING AND DESCRIPTION OF MOTIONS OF THE SHOULDER MECHANISM

A measurement technique is presented for recording positions of the bo nes of the shoulder mechanism, i.e., thorax, clavicula, scapula and hu merus, in 3-D space, based on palpating and recording positions of bon y landmarks. The palpation technique implies that only static position s can be measured. Accuracy of retrieving bony landmarks is checked on -line using rigid body assumptions. The measurement error is calculate d afterwards and is comparable with cinegraphic methods. Axial rotatio n of the clavicula is estimated by minimizing rotations in the acromio clnviacularjoint. A number of motion definitions is compared by means of interindividual variation and subjective interpretability. Two usef ul definitions are proposed for describing motions of the shoulder mec hanism. Four conditions have been recorded: abduction and anteflexion of the humerus both with and without additional weight in the hand. Ab duction and anteflexion result in large differences in scapular and cl avicular motions. The effect of additional weight in the hand on the p osition of the shoulder girdle is negligible.