Arthritis describes a condition where the cartilage that covers the ends of bones where they form a joint deteriorates, affecting joint function. In the shoulder this can occur in the ball and socket joint (glenohumeral joint) or the joint where the collarbone meets the corner of the shoulder blade (acromioclavicular joint). Glenohumeral joint arthritis will generally have a more profound affect on shoulder function with greater degrees of pain and loss of function.