One of the factor that contributes to the variety of movement the hand can perform “around” the body is the huge mobility of the shoulder.
What we generically identify as shoulder movements are separate in 2 different “sectors” and involve 4 joints (3 anatomical joints and 1 “functional” joint):
- Movements between humerus and scapula, the Glenohumeral Joint: this is the proper “shoulder joint” and it is responsible of the majority of movements.
- Movements between the scapula and the trunk (thorax): in physiological movement these movements contribute for 1 third of the range of motion of the shoulder complex. The Scapolo-Thoracic joint is not an “anatomical” joint and, in reality, its movements are allowed by other 2 “real/anatomical” joints:
- Sternoclavicular joint
- Acromionclavicular joint
Since the Sternoclavicular and Acromiolcavicular joints have practically no muscles acting directly on them, all movements between Scapula and Thorax are here described in the Scapulo-thoracic joint that is more easily evaluable and testable.