| Lower extremity (bone) |
| Osteomyelitis |
| Fracture, including occult fracture (child abuse) and stress fracture |
| Traction apophysitis |
| Sinding-Larsen-Johansson disease (inferior patella) |
| Sever disease (calcaneus) |
| Osgood-Schlatter disease (tibial tuberosity) |
| Iselin disease (base of the 5th metatarsal) |
| Osteochondrosis |
| Freiberg disease (head of the 2nd metatarsal) |
| Köhler disease (navicular bone of the foot) |
| Slipped capital femoral epiphysis |
| Idiopathic avascular necrosis of the hip (Legg-Calvé-Perthes disease) |
| Benign and malignant tumors |
| Leukemia |
| Metastatic neuroblastoma |
| Osteogenic sarcoma |
| Ewing sarcoma |
| Osteoid osteoma |
| Limb length discrepancy |
| Pathologic varus (bow legs) |
| Pathologic valgus (knock knees) |
| Tarsal coalition |
| Torsional deformities |
| Vasoocclusive crisis (sickle cell disease) |
| Lower extremity (joint) |
| Transient synovitis of the hip |
| Bacterial (septic) arthritis |
| Lyme arthritis (endemic regions) |
| Osteochondritis dissecans |
| Developmental dysplasia of the hip |
| Oligoarticular juvenile idiopathic arthritis (JIA) and other rheumatic diseases (eg, systemic lupus erythematosus, systemic JIA) |
| Immunoglobulin A vasculitis (Henoch-Schönlein purpura) |
| Serum sickness and serum sickness-like reactions |
| Reactive arthritis |
| Acute rheumatic fever |
| Joint hypermobility syndrome |
| Hemarthrosis (causes include trauma, hemophilia, and, rarely, pigmented villonodular synovitis) |
