Etiology
The etiology of bursitis is unknown. The term bursitis suggests inflammation in one of several bursae in the body. This inflammation may be caused by a number of different processes:
Repetitive injury or acute trauma: any repetitive pattern of movement that puts pressure on a bursa, such as compression of the subacromial bursa under the coracoacromial arch. An alteration in gait pattern caused by lower limb discrepancy or iliotibial band contracture may affect the stresses on the subtrochanteric bursa. Certain professions have been thought to be more at risk of certain types of bursitis due to repetitive action in their daily work; this led to the colloquial naming of "clergyman's knee" and "student's elbow" for infrapatellar and olecranon bursitis, respectively. Poorly fitting footwear can cause retrocalcaneal bursitis by exerting excessive pressure on the heel.
Crystal deposition secondary to gout or calcium pyrophosphate deposition disease: crystal arthropathy can result in crystal deposition within the bursa and subsequent inflammation of the synovial lining, resulting in bursitis. Bursitis can also be the first presenting feature of a crystal arthropathy.
Autoimmune disease: e.g., rheumatoid arthritis has been associated with bursitis.
Infection, acute or chronic: may follow a penetrating injury from a foreign body.
Osteoarthritis of the hip: has been implicated as a cause of trochanteric bursitis through osteophyte deposition, but this remains unproven.
No association has been demonstrated with diabetes, knee osteoarthritis, or obesity.[4]
Pathophysiology
Little is known about the molecular and biochemical pathophysiology of bursitis. The bursal wall becomes thickened, with proliferation of its synovial lining, bursal adhesions, villus formation, tags, and chalky deposits. Inflammation is thought to result in synovial proliferation and increased fluid production, which accounts for the swelling seen in superficial bursitis. Bursitis can occasionally cause inflammation in a communicating joint.[5][6][7][8]
An inflammatory basis is supported by the marked relief often obtained by injections containing anti-inflammatory corticosteroid. However, one study found no histologic evidence of inflammation.[5][7]
Classification
Anatomic classification
There is no formal classification system for bursitis, but it may be described according to the site of the affected bursa. The most commonly encountered are:
Prepatellar bursitis ("housemaid's knee")
Infrapatellar bursitis ("clergyman's knee")
Anserine bursitis (anserine refers to the classic appearance of a swollen bursa being restrained by the 3 tendons overlying it - sartorius, gracilis, and semitendinosus - creating the impression of a goose's foot)
Olecranon bursitis ("student's elbow")
Retrocalcaneal bursitis
Trochanteric bursitis
Subacromial (subdeltoid) bursitis.
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