Bursitis

Anatomy

Bursae are small sacs lined with synovium, a thin membrane that secretes a clear, viscous (thick) lubricating substance called synovial fluid. They are located in areas of friction where skin, tendons, and ligaments move across bony prominences. If bursitis becomes chronic, the synovial fluid within the bursa can become thickened and calcified from prolonged swelling. The most commonly affected bursae are the subacromial, olecranon, trochanteric, prepatellar, infrapatellar, pes anserine, and retrocalcaneal.

The subacromial bursa is located in the shoulder, just inferior (below) to the acromion of the scapula (shoulder blade) and above the rotator cuff. The olecranon bursa is located just under the skin at the posterior (back) elbow at the olecranon of the ulnar bone. The trochanteric bursa lies over the greater trochanter of the lateral (outer) hip. The prepatellar bursa is located between the skin and the patella (knee cap) and the infrapatellar bursa is just inferior (toward the foot) to the patella, surrounding the patellar tendon. The pes anserine bursa is located on the medial (inner) leg, just inferior to the knee. It lies between the tibia bone and the attachment of three muscle tendons: semitendinosus of the hamstrings, gracilis, and sartorius.

Symptoms

Initially, symptoms of bursitis will be noticed only during activity or when pressure is applied directly over the bursa. For example, it is common for people with trochanteric bursitis to complain of hip pain when they lie on the affected side. Pain is also noted to worsen after a period of inactivity, such as stepping out of a car after a long trip. Edema (swelling), erythema (redness), and radiating pain to adjacent structures may also occur. As the inflammation progresses, symptoms become more severe, occurring at rest or with minimal movement. This is seen in subacromial bursitis, in which patients commonly report pain that awakens them at night. Prolonged inflammation can lead to thickening of the synovium, calcification of the synovial fluid, and chronic swelling. In these cases, the bursa is no longer acting as a lubricating pad. Partial tears or complete rupture of adjacent muscles or tendons may then occur from excess friction. In this case, weakness would be reported in addition to pain.

Causes

Bursitis can be caused any mechanism that can irritate a bursa. The most common cause is trauma, either repetitive or acute. Examples of areas of repetitive trauma are the acromial bursa of the shoulder in throwing athletes and the knee or hip in runners. Bursitis from acute trauma is more commonly seen over bony prominences such as the greater trochanter or olecranon after a fall. Other causes include infection, gout, and rheumatoid arthritis, as well as other medical conditions that involve the immune system.

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