A simple joint effusion also arises from the elbow joint, but this diagnosis becomes less likely when the joint aspirate appears cloudy. A simple joint effusion would not produce bacteria on gram stain and culture.
Crystalline inflammatory arthritis (gout, pseudogout) is due to intra-articular precipitation of crystals (uric acid crystals in gout, calcium pyrophosphate crystals in pseudogout).
Hematomas would produce gross blood or clot on joint aspiration.
Cellulitis is an infection of the superficial soft tissue (only) and thus, aspiration is not likely to yield fluid.
Diagnosis can be made with culture of fluid
Confirmation of septic olecranon bursitis is best attained by bursal needle aspiration and culture. Aspiration also can evaluate for other causes of elbow swelling. (If septic olecranon bursitis is suspected clinically, empiric antibiotics should be started while awaiting culture results.6) White blood cell counts from the aspirate also may be utilized but have a lower sensitivity and specificity for diagnosis.7
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