• Knee effusion

Reference

• Reproduced from Rodnan GP (ed): Primer on the Rheumatic Diseases, 7th ed. JAMA. 1973;224(Suppl):662.

Group I: Noninflammatory

• Osteoarthritis
• Trauma (may be hemorrhagic)
• Osteochondritis dissecans
• Osteochondromatosis
• Neuropathic arthropathy (may be hemorrhagic)
• Subsiding or early inflammation
• Hypertrophic osteoarthropathy (group I or II)
• Pigmented villonodular synovitis (may be hemorrhagic)

Group II: Inflammatory

• Rheumatoid arthritis
• Gout or pseudogout
• Reactive arthritis (Reiter’s syndrome)
• Ankylosing spondylitis
• Psoriatic arthritis
• Arthritis accompanying inflammatory bowel disease
• Rheumatic fever (group I or II)
• Systemic lupus erythematosus (group I or II)
• Scleroderma (group I or II)
• Tuberculosis
• Mycotic infection

Group III: Purulent

• Pyogenic bacterial infection

Hemorrhagic

• Hemophilia or other bleeding disorder
• Trauma with or without fracture
• Neuropathic arthropathy
• Pigmented villonodular synovitis
• Synovioma
• Hemangioma and other benign neoplasms