Acute Monoarthritis: Diagnosis in Adults.

Acute monoarthritis can be the initial manifestation of many joint disorders. The most common diagnoses in the primary care setting are osteoarthritis, gout, and trauma. It is important to understand the prevalence of specific etiologies and to use the appropriate diagnostic modalities. A delay in diagnosis and treatment, particularly in septic arthritis, can have catastrophic results including sepsis, bacteremia, joint destruction, or death. The history and physical examination can help guide the use of laboratory and imaging studies. The presence of focal bone pain or recent trauma requires radiography of the affected joint to rule out metabolic bone disease, tumor, or fracture. If there is a joint effusion in the absence of trauma or recent surgery, and signs of infection (e.g., fever, erythema, warmth) are present, subsequent arthrocentesis should be performed. Inflammatory synovial fluid containing monosodium urate crystals indicates a high probability of gout. Noninflammatory synovial fluid suggests osteoarthritis or internal derangement. Pitfalls in the diagnosis and early treatment of acute monoarthritis include failure to perform arthrocentesis, administering antibiotics before aspirating the joint when septic arthritis is suspected (or failing to start antibiotics after aspiration), and starting treatment based solely on laboratory data, such as an elevated uric acid level.