Acute osteoarthritis
Avascular necrosis
Crystal-induced (Gout, Pseudogout)
Gonococcal arthritis, arthritis-dermatitis syndrome
Nongonococcal septic arthritis
Lyme disease
Malignancy (metastases, osteochondroma, osteoid osteoma)<unk> ctive poststreptococcal arthritis
Trauma-induced arthritis
Fracture
Ligamentous injury
Overuse
Avascular necrosis
Decompression sickness
Spontaneous osteonecrosis
Hemorrhagic (e.g. hemophilia, systemic anticoagulation
Seronegative spondyloarthropathies (ankylosing spondylitis, IBD, psoriatic arthritis,<unk> 
RA, SLE
Sarcoidosis, amyloidosis
Periarticular pathology
Cellulitis
Tendonitis
Bursitis
Transient (Toxic) Synovitis (Hip)
Slipped Capital Femoral Epiphysis (SCFE)
Legg Calve Perthes Disease
Fracture
Ligamentous injury
Overuse
Cellulitis
Tendonitis
Bursitis
Ankylosing spondylitis
Gonococcal arthritis
Lyme disease
Psoriatic arthritis<unk> 
Rheumatic fever
Rheumatoid arthritis
Systemic lupus erythematosus
Fibromyalgia
Juvenile idiopathic arthritis
Lyme disease
Osteoarthritis
Psoriatic arthritis<unk> ctive poststreptococcal arthritis
Rheumatoid arthritis
Rheumatic fever
Serum sickness
Systemic lupus erythematosus
Serum sickness–like<unk> ctions
Viral arthritis
Gonococcal arthritis
Lyme disease
Rheumatic fever
Systemic lupus erythematosus
Viral arthritis
Reactive arthritis
Acute osteoarthritis
Rheumatoid arthritis
Avascular necrosis
Juvenile idiopathic arthritis
Crystal-induced 
Reactive poststreptococcal arthritis
Gonococcal arthritis, arthritis-dermatitis syndrome