Shoulder Anatomy


The shoulder is a ball and socket joint with a very shallow socket which allows a large range of motion and has the tendency to dislocate if the ligaments become injured. The rotator cuff tendons, especially the supraspinatus tendon, do not have much room under the acromion of the scapula (shoulder blade). This leads frequently to tendinitis, tears of the rotator cuff, and inflammation of the subacromial bursa (bursitis).

Shoulder Tendinitis/Bursitis The tendons of the rotator cuff, which rotate the upper humerus and help raise the arm by pulling the humeral head down as the deltoid muscle pulls the arm up, can be irritated by pressure from the acromion process of the scapula and the coraco–acromial ligament . This irritation of the tendons and/or of the bursa is known as “Tendinitis” and/or “Bursitis”.

Symptoms Pain, usually with motion and at night, but sometimes constantly. There may be snapping sensations with motion. Often the symptoms start after an injury due to the resultant weakening of the shoulder muscles caused by the pain from the injury.

Diagnosis

  • Physical examination.
  • X–rays.
  • Arthrogram

Treatment Oral or injected anti–inflammatory medications, and strengthening of the shoulder musculature. If these fail, surgical removal of the offending acromial prominences or spurs, either by open or arthroscopic means may be done. If the tendinitis is due to a shoulder instability problem, surgical correction of the ligamentous laxity may be necessary if strengthening is not helpful.

Shoulder Dislocation

The humeral head is held in the shallow gleaned socket by ligaments. If these ligaments are detached from the glenoid by injury, or are lax due to genetic or developmental causes, the head of the humerus may slip out of the socket completely (dislocation) or incompletely (subluxation). The most common direction of instability is anterior, with posterior and inferior being much less common. In anterior instability due to injury the ligamentous attachments to the glenoid rim are torn loose. When the arm is raised to the side in external rotation, similar to the position one assumes to prepare to throw a ball, the humeral head is forced out through the area of ligamentous attachment.

Diagnosis

  • History.
  • Physical examination.
  • MRI.
  • X–ray views.
  • Examination under anesthesia.

Treatment Surgical, whereby the ligamentous glenoid labrum is re–attached to the glenoid (socket) rim. In cases of subluxation which are not caused by injury, exercises to strengthen the shoulder muscles are often helpful. If not, or in post–injury subluxation not cured by exercise, stabilization by ligament reattachment or tightening may be needed.

Although arthroscopic shoulder stabilization is technically feasible, it is still in the developmental stage and not widely done, since the success rate for this operation has not been high enough for open stabilization, especially in active, athletic patients, and since the recovery is not significantly shortened by arthroscopic means.