The third most common site of injury is the link between the arm and trunk, the shoulder.
Most shoulder injuries occur due to overuse.
Overuse injuries happen when muscles, tendons and joints are subjected to repetitive stresses. When the stresses applied to a body part supersede the body's ability to recover from these stresses damage and injury can result. The most common overuse injury in the shoulder is rotator cuff tendinitis . Arthritis rarely occurs in the actual ball and socket of the shoulder joint because, unlike our hips and knees, the shoulder does not have to bear the full weight of our body. However, arthritis can and does commonly occur in a joint located at the top of the shoulder called the acromioclavicular or AC joint.