Bursitis - Causes

Activities that put constant and/or repetitive pressure on a joint (such as kneeling, or resting your elbow on a desk).
Repetitive and vigorous joint movement (such as hammering or swinging a tennis racquet).
A blow or other injury to a joint.
Arthritis, gout and certain infections.
Calcium deposits in (or degeneration of) an adjacent tendon

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See also treatment and what is bursitis?