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Bursitis is an inflammatory reaction in a fluid-filled synovial sac, commonly over the subacromial, prepatellar, olecranon, or trochanteric bursa. It is associated with repetitive motion, trauma, or infection. The fluid collection may be bacterial (septic bursitis), gouty, or, most commonly, inflammatory. It produces pain, tenderness, swelling, warmth, and limited range of motion. It is critical to differentiate septic from benign inflammation.
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Because bursitis does not involve the intra-articular space, signs and symptoms should be isolated to the bursal area. Typically, intra-articular involvement is associated with pain on minor range of motion, while the discomfort of bursitis occurs with skin and synovial sac stretching at extreme ranges of joint movement. When this differentiation is difficult, fluid aspiration and analysis for cell count, Gram stain, protein, glucose, and polarized microscopy (see Gout in Rheumatologic Conditions) may be helpful. Fluid with greater than 50,000 cells per cubic millimeter, polymorphonuclear neutrophil predominance, increased protein, reduced glucose, and a positive Gram stain are associated with bacterial infection.
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Management and Disposition
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Rest, compression dressings, and nonsteroidal anti-inflammatory drugs (NSAIDs) are initially used. Bursal injection of local anesthetics mixed with corticosteroids can be considered if septic bursitis has been ruled out, usually in patients who have failed treatment with NSAIDs. Reducing the effusion volume by aspiration may provide temporary relief, although it often recurs. Septic bursitis requires aspiration, gram-positive antibiotic coverage, and consideration of open incision and drainage by orthopedic surgery. Most patients can be treated as outpatients with follow-up.
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Septic joint infections in patients who are immunocompromised may have lower synovial fluid leukocyte counts (<30,000/mm3) than usual (>50,000/mm3).
Bursal fluid from a septic bursitis typically has a lower nucleated cell count than septic joint fluid; lower limits of 2000/mm3 have been proposed.
S aureus is the most common etiologic agent of septic bursitis.
Ultrasound can be used to differentiate between prepatellar and joint effusions.