In evaluating chronic monoarticular arthritis, what initial studies should be obtained?
• Radiograph of the joint: Radiographs are often revealing in chronic arthritis. Chronic infections by mycobacteria and fungi often cause radiographically detectable abnormalities. Osteoarthritis, avascular necrosis of bone, and other causes of noninflammatory chronic arthritis also have characteristic radiographic appearances. Radiographs of the contralateral joint for comparison may be helpful.
• Synovial fluid analysis, when possible: This analysis is useful in dividing possible causes of the joint process into the two broad diagnostic categories—inflammatory and noninflammatory arthritis. A bloody synovial effusion points to pigmented villonodular synovitis, synovial chondromatosis, synovial sarcoma, or neuropathic joint. Cultures of synovial fluid may demonstrate mycobacterial or fungal infection.