What physical findings are useful in the differential diagnosis of chronic monoarticular arthritis?
• Extraarticular features of the spondyloarthritis family, such as skin rashes (psoriasis, keratoderma blennorrhagicum), oral ulcers, urethral discharge, conjunctivitis, uveitis
• Erythema nodosa, a feature of sarcoidosis and inflammatory bowel syndrome
• A positive McMurray maneuver in the knee examination, suggesting internal derangement
