Anatomy of Joints: The Shoulder Girdle
The shouder girdle is made out of the clavicle and the scapula. However, all movements of the scapula are usually considered movements of the shoulder girdle. They include elevation, depression. upward rotation, downward rotation, protraction (abduction) and retraction (adduction).
Because the shoulder is designed for mobility, its stability is reduced. The muscular arrangements of the shoulder girdle and the shoulder joint are such that they provide the stability lacking as a result of the weak arrangements of the bones and ligaments. However, the muscles must be strong enough to provide the necessary stability. A lack of upper body strength accounts for many of the injuries in the shoulder region.
Injury to the ligaments of and muscles of the shoulder girdle is possible if the stabilizing components of the muscles are not strong enough to hold the joint together. Also, since the shoulder girdle is fairly mobile relative ti the trunk, in many instances it must be a stable base against which the muscles of the shoulder joint pull. During forceful overarm motions the strength of the agonistic and antagonistic muscles surrounding the shoulder girdle prevents overuse strains on the surrounding tissues.
In most activities involving the upper extremity, the shoulder girdle is the responsible for the initiation of the movement. For example, elevation of the scapula initiates lifting the arm; depression precedes pulling the arm downward; protraction occurs before reaching, throwing or pushing forward; retraction initiates pulling backward; upward rotation takes place for increasing the range if overhead reaching; and downward rotation allows for forceful arm adduction at the shoulder joint.
Relation between the Shoulder Joint and the Shoulder Girdle
The shoulder joint muscles are responsible for moving the arm while the shoulder girdle muscles (which work in synchronization with the shoulder joint muscles) are responisble for moving the scapula and clavicle. The muscles work closely with one another to ensure smooth, fulll range of motion in the shoulder joint.
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