Although the shoulder is the most movable joint in the body, it is also an unstable joint because of its range-of-motion. Because the ball of the upper arm is larger than the socket of the shoulder, it is susceptible to injury. The shoulder joint must also be supported by soft tissues - muscles, tendons, and ligaments - which are also subject to injury, overuse, and under use.

Common shoulder problems include the following:

  • Dislocation - The shoulder joint is the most frequently dislocated major joint of the body - often caused by a significant force that separates the shoulder joint's ball (the top rounded portion of the upper arm bone, or humerus) away from the joint's socket (glenoid). 
  • Separation - The shoulder becomes separated when the ligaments attached to the collarbone (clavicle) are torn, or partially torn, away from the shoulder blade (scapula). Shoulder separation may be caused by a sudden, forceful blow to the shoulder, or as a result of a fall.
  • Bursitis - Bursitis often occurs when tendonitis and impingement syndrome cause inflammation of the bursa sacs that protect the shoulder.
  • Impingement Syndrome - Impingement syndrome is caused by the excessive squeezing or rubbing of the rotator cuff and shoulder blade. The pain associated with the syndrome is a result of an inflamed bursa (lubricating sac) over the rotator cuff, and/or inflammation of the rotator cuff tendons, and/or calcium deposits in tendons due to wear and tear. Shoulder impingement syndrome can lead to a torn rotator cuff.
  • Tendonitis - Tendonitis of the shoulder is caused when the rotator cuff and/or biceps tendon become inflamed, usually as a result of being pinched by surrounding structures. The injury may vary from mild inflammation to involvement of most of the rotator cuff. When the rotator cuff tendon becomes inflamed and thickened, it may become trapped under the acromion.
  • Rotator Cuff Tear - A rotator cuff tear involves one or more rotator cuff tendons becoming inflamed from overuse, aging, a fall on an outstretched hand, or a collision.
  • Adhesive Capsulitis (Frozen Shoulder) - Frozen shoulder is a severely restrictive condition frequently caused by injury that, in turn, leads to lack of use due to pain. Intermittent periods of use may cause inflammation and adhesions to grow between the joint surfaces, thus restricting motion. There is also a lack of synovial fluid to lubricate the gap between the arm bone and socket that normally helps the shoulder joint to move. This restricted space between the capsule and ball of the humerus distinguishes adhesive capsulitis from the less complicated condition known as stiff shoulder.
  • Fracture - A fracture is a partial or total crack or break through a bone that usually occurs due to a impact injury.

Degenerative conditions and other diseases in the body may also contribute to shoulder problems, or generate pain that travels along nerves to the shoulder.