The upper limb and scapula (the shoulder blade) is connected to the trunk through the collar bone. The AC Joint ( AcromioclacularJoint) is between the collar bone and the Acromion (the pointed part of the shoulder blade) The upper limb is connected to the trunk through strong muscles.

The major muscle groups that move the arm includes: the deltoid muscle, pectoralis muscles and the lattisimus dorsi muscle.

Commonly thought of as a single joint, the shoulder is actually made up of two separate joints – the glenohumeral and acromioclavicular joints. These two joints work together to allow the arm to move through a large circle and to rotate around at the shoulder.

The acromioclavicular joint gives the shoulder joint additional flexibility.

Although both of these joints are held together by extensive ligament and muscle attachments, exessive force applied can easily weaken or tear these ligaments and musces of the shoulder. The shoulder joint is vulnerable to dislocations from sudden jerks of the arm, especially inyoung adults before strong muscles have developed. Dislocation of the shoulder is extremely painful and may require surgical repair or cause permanent damage.

Chronic wear and tear on the glenohumeral joint can lead to the painful tearing of the tendons of the rotator cuff or a torn labrum. Both of these conditions are very painful and may require surgery to remove or reattach the torn tissue.