Snapshot A 9-year-old boy presents to his pediatrician with a limp and hip pain. He denies any inciting trauma or event. On exam, he is noted to have atrophy in his upper thigh, asymmetry in leg lengths, and decreased range of motion in his left hip. Radiograph shows sclerosis in the femoral head. His physician recommends conservative management. Introduction Clinical definition an idiopathic hip disorder characterized by avascular necrosis of the femoral head Epidemiology Demographics male > female affects children ages 3-12 but most commonly between ages 4-8 most commonly unilateral Risk factors obesity thrombophilia factor V Leiden mutation South Asian heritage Etiology Unknown but thought to be related to factors that can disrupt bone formation or blood supply to the femoral head, including coagulation abnormalities or trauma Pathogenesis blood flow to the femoral head is disrupted causing ischemic necrosis femoral head begins healing after ~1 year and new subchondral bone develops new bone replaces the old bone in 2-3 years Associated conditions acetabular retroversion inguinal hernia Down syndrome cryptorchidism Presentation Symptoms limping pain in the hip that is worse with activity referred knee pain Physical exam small for age thigh and calf muscle atrophy shortening of the leg (asymmetry) hip stiffness and limited range of motion reduced abduction and internal rotation gait disturbance may have Trendelenburg sign no erythema or swelling Imaging Radiography indication for evaluation of femoral head involvement findings femoral head sclerosis collapse of lateral pillar of femoral head increased width of the femoral neck Magnetic resonance imaging indications for evaluation during early stages of the disease when radiography is unrevealing if the diagnosis is uncertain after radiography findings decreased signal intensity in the femoral head due to sclerosis Technetium bone scan decreased uptake at the epiphysis Studies Labs typically normal erythrocyte sedimentation rate and C-reactive protein Making the diagnosis based on clinical presentation and imaging studies Differential Sickle cell disease distinguishing factors anemia sickle cells on peripheral blood smear Slipped capital femoral epiphysis distinguishing factors in obese adolescents displacement of femoral head relative to the femoral neck on radiography Treatment Management approach treatment is usually conservative but may be treated with surgery Conservative observation and bed rest indication children who were less than 6 years of age at disease onset physical therapy or brace/cast indication for all patients Medical nonsteroidal anti-inflammatory drugs indication pain management Operative surgical treatment indication older children (6 years of age or older) or with more advanced disease surgeries pelvic osteotomy (Salter osteotomy) trochanteric advancement surgery Complications Permanent femoral head deformity and limp Osteoarthritis due to deformity of the femoral head Prognosis Over half heal without surgical intervention