Noninflammatory: < 2,000 WBC per mm3 (2 x 109 per L)	Inflammatory: > 2,000 WBC per mm3
Osteoarthritis	Septic arthritis*
Trauma	Crystal-induced monoarthritis (e.g., gout, pseudogout)
Avascular necrosis	Rheumatoid arthritis
Charcot’s arthropathy	Spondyloarthropathy
Hemochromatosis	Systemic lupus erythematosus
Pigmented villonodular synovitis	Juvenile rheumatoid arthritis, Lyme disease, other crystalline arthritides