Infection Septic arthritis (bacterial) Staphylococcus aureus Streptococcus pneumoniae Haemophilus influenza Group B streptococci Escherichia coli Neisseria gonorrhea Other infectious arthritis Viral Mycobacterial Fungal Osteomyelitis Postinfectious Viral: hepatitis B, parvovirus, Epstein–Barr virus, cytomegalovirus, varicellazoster, herpesvirus 6, enterovirus, adenovirus Bacterial: acute rheumatic fever, Lyme disease, chlamydia (Reiter syndrome), mycoplasma, shigella, campylobacter Trauma/overuse Contusion Hemarthrosis Fracture Inflicted injury Ligamentous sprain Bursitis Tendonitis Slipped capital femoral epiphysis Legg–Calvé–Perthes disease Osteochondritis dissecans Chondromalacia patellae Osgood–Schlatter disease Immune mediated/vasculitic Juvenile idiopathic arthritis Serum sickness Kawasaki disease