The shoulder complex in elevation of the arm: A mechanism approach

A qualitative kinematical model for the shoulder complex in elevation is presented. The need for such a model was realised during the biomechanical assessment of the glenohumeral joint due to the inaccessibility of the shoulder region to the common methods of following bone movements. The shoulder complex is described as a two mechanism system, the first consisting of the skeleton, clavicle and scapula, and the second the scapula (or scapula plus clavicle) and humerus. Elevation of the arm is divided into four phases during which the scapula and clavicle behave intermittently as separate links and a structure. It is proposed that during the whole activity the serratus anterior lower acts as the prime mover of the shoulder girdle.