proximal tibia, both classically affecting young adolescents Osteochondrosis can involve the foot bones in three locations: The tarsal navicular bone (Kohler disease) in younger children and the metatarsal heads (Freiberg disease) or the calcaneal apophysitis (Sever disease) in adolescents Both benign and malignant bone tumors may present with a painful limp Benign lesions include bone cysts (unicameral or aneurysmal), fibrous dysplasia, and eosinophilic granulomas Osteoid osteoma, caused by a painful nidus of vascular osteoid tissue, is another benign lesion unique to young people The most common malignant pediatric bone tumors are osteogenic sarcoma and Ewing sarcoma Bone tumor pain may be acute or chronic, with acute pain usually related to a pathologic fracture Examples of acquired skeletal abnormalities causing painful limp include tarsal coalition and osteochondritis dissecans Tarsal coalition occurs as a result of gradual calcification of a congenital cartilaginous bar between tarsal bones; it presents most commonly as a painful flatfoot in school-aged children Osteochondritis dissecans is related to osteonecrosis of the subchondral bone with separation of articular cartilage from underlying bony lesion; it most commonly affects the knees of adolescent boys Localized findings without pain suggest congenital or slowly developing acquired limb abnormalities Three disorders of the hip fit into this category, each of which is characteristic of a specific age group Developmental dysplasia of the hip includes a spectrum of abnormalities, ranging from mild dysplasia to frank dislocation Most affected children with access to primary care are diagnosed with abnormal hip abduction on routine examination in infancy Occasionally, the diagnosis will be missed, and the child then presents at the onset of walking with a painless short-leg limp, or waddling gait if bilateral, with weakness of the abductor musculature Legg–Calvé–Perthes disease, an avascular necrosis of the capital femoral epiphysis, presents in young school-age children as an insidious limp with mild, activity-related pain Slipped capital femoral epiphysis (SCFE) presents in young, typically obese adolescents with an externally rotated limp The amount of pain experienced is related to the rate of displacement of the epiphysis, ranging from none to severe Legg–Calvé–Perthes disease and SCFE are more common in boys Other acquired skeletal deformities that may cause painless limp include limb-length inequality, Blount disease (with marked bowing of the proximal tibias), and torsional deformities Baker cyst of the popliteal tendon may cause limping with minimal local discomfort