The shoulder joint is a ball-and-socket joint, capable of moving in any direction. It is formed by the humerus – upper arm bone – and the glenoid fossa – part of the shoulder blade bone. Bursa sacs are small, fluid-filled cushions that provide padding between bones and tendons in a joint to reduce friction and improve movement. Shoulder bursitis develops when the bursa sac becomes inflamed.
Anatomy
The acromion bone – part of the shoulder blade – forms a “roof” over the ball of the shoulder joint. According to Orthopedic Reviews, the short distance between these bones ranges from 0.4 to 0.6 inches. The subacromial bursa sits underneath this roof, on top of the supraspinatus tendon, which connects muscle to the humerus. The rotator cuff muscles – supraspinatus, infraspinatus, teres minor and subscapularis – provide dynamic stability to the shoulder joint, keeping it “in place” as the arm moves. The subacromial bursa provides padding for the supraspinatus tendon to keep it from rubbing against the acromion bone.
Location
Although the subacromial bursa cannot be seen by looking at the shoulder from any angle, its general location can be identified by touching the shoulder. The acromion bone can be felt at the upper outside edge of the shoulder. The subacromial bursa sac is located directly underneath this ledge. Bursitis can cause swelling and pain in this area of the shoulder.
Symptoms & Diagnosis
A main complaint associated with shoulder bursitis is sharp, burning pain midway between the shoulder and elbow, referring from the shoulder joint. This pain is present during activity and also at rest, often disrupting sleep. Range of motion may be decreased due to pain or associated damage to the rotator cuff tendons. Shoulder bursitis is diagnosed by clinical examination. Active movement of the shoulder out to the side – abduction – is typically painful from 80 to 120 degrees. During this arc of motion, the humerus is in close proximity to the acromion. Patients may also complain of a “catching” sensation as they lower their arm back down. X-rays and MRI are sometimes performed to rule out bone spurs or rotator cuff pathology, but aren’t typically used just to confirm a diagnosis of bursitis.
Treatments
Treatment of bursitis is based on the underlying cause. For example, septic bursitis, related to an infection, is treated with antibiotic medication. Physical therapy is frequently prescribed to treat shoulder bursitis. Treatments such as heat, ultrasound, electrical stimulation and ice are used to reduce pain and increase blood flow to the shoulder joint and the bursa. Stretches are performed to improve flexibility and movement of the shoulder. Strengthening exercises focus on the rotator cuff muscles, but positions of impingement – shoulder elevation – are avoided to prevent further damage. Cortisone injections are sometimes administered by a physician to decrease inflammation in the bursa. Surgical intervention is sometimes required to treat shoulder pain caused by subacromial impingement syndromes. Subacromial decompression surgery is often performed arthroscopically, using small portal holes for a camera and shaver – without the need for a large incision. The underside of the acromion is shaved and smoothed over, and any bone spurs are removed to relieve pressure in the subacromial space. Physical therapy is prescribed after surgery to improve range of motion and restore shoulder function.