Acute osteoarthritis
Avascular necrosis
Crystal-induced (Gout, Pseudogout)
Gonococcal<unk> ,<unk> -dermatitis syndrome
Nongonococcal septic<unk> 
Lyme disease
Malignancy (metastases, osteochondroma, osteoid osteoma)
Reactive poststreptococcal<unk> 
Trauma-induced<unk> 
Fracture
Ligamentous injury
Overuse
Avascular necrosis
Decompression sickness
Spontaneous osteonecrosis
Hemorrhagic (e.g. hemophilia, systemic anticoagulation
Seronegative spondyloarthropathies (ankylosing spondylitis, IBD, psoriatic<unk> , reactive<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
Gonococcal<unk> 
Nongonococcal<unk> <unk> -Dermatitis Syndrome
Gout
Pseudogout
Fracture
Ligamentous injury
Overuse
Avascular necrosis
Decompression sickness
Spontaneous osteonecrosis
pain in absence of trauma
femoral head, medial conyle of knee
pain in absence of trauma
femoral head, medial conyle of knee
Posttraumatic
Hemophilia
Systemic anticoagulation
Metastases
Osteochondroma
Osteoid osteoma
Pigmented villonodular synovitis
Remote infection, infectious endocarditis
Rheumatic fever
Seronegative (no RF) spondyloarthropathies (ankylosing spondylitis, IBD, psoriatic, reactive<unk> 
Rheumatoid<unk> , SLE
Sarcoidosis, amyloidosis
Cellulitis
Tendonitis
Bursitis
Transient (Toxic) Synovitis (Hip)
Slipped Capital Femoral Epiphysis (SCFE)
Legg Calve Perthes Disease
Monoarticular arthritis
Acute osteoarthritis
Septic arthritis 
Avascular necrosis
Septic arthritis
Crystal-induced 
Reactive arthritis
Gonococcal arthritis, arthritis-dermatitis syndrome