summary Hip Osteonecrosis, also known as avascular necrosis of the hip, represents a condition caused by reduced blood flow to the femoral head secondary to a variety of risk factors such as a traumatic event, sickle cell disease, steroid use, alcoholism, autoimmune disorders, and hypercoagulable states. Diagnosis can be made with plain radiographs in moderate/late disease but MRI may be required to detect early or subclinical osteonecrosis. Treatment is generally observation with management of the underlying systemic condition. Operative management is indicated for advanced disease with presence of subchondral collapse, femoral head flattening and/or degenerative joint disease. Epidemiology Incidence 20,000 new cases per year in the United States accounts for 10% of total hip arthroplasties performed Demographics male > females average age at presentation is 35 to 50 Anatomic location bilateral hips involved 80% of the time multifocal osteonecrosis disease in three or more different joints 3% of patients with osteonecrosis have multifocal involvement Risk factors direct causes irradiation trauma hematologic diseases (leukemia, lymphoma) dysbaric disorders (decompression sickness, "the bends") - Caisson disease marrow-replacing diseases (e.g. Gaucher's disease) sickle cell disease indirect causes alcoholism hypercoagulable states steroids (either endogenous or exogenous) systemic lupus erythematosus (SLE) transplant patient virus (CMV, hepatitis, HIV, rubella, rubeola, varicella) protease inhibitors (type of HIV medication) idiopathic Etiology Pathophysiology idiopathic AVN intravascular coagulation is the final common idiopathic pathway pathoanatomic cascade login to view 7 more bullets AVN associated with trauma due to injury of femoral head blood supply (medial femoral circumflex) Associated conditions AVN rates of specific traumatic injuries femoral head fracture: 75-100% basicervical fracture: 50% hip dislocation: 2-40% (2-10% if reduced within 6 hours of injury) intertrochanteric fracture: rare higher risk of AVN with greater initial displacement and poor reduction decompression of intracapsular hematoma may reduce risk quicker time to reduction may reduce risk Classification Steinberg Classification (modification of Ficat classification) Stage Radiographs MRI 0 Normal Normal MRI and bone scan I Normal Abnormal MRI and/or bone scan II Cystic or sclerosis changes Abnormal MRI and/or bone scan III Crescent sign (subchondral collapse) Abnormal MRI and/or bone scan IV Flattening of femoral head Abnormal MRI and/or bone scan V Narrowing of joint Abnormal MRI and/or bone scan VI Advanced degenerative changes Abnormal MRI and/or bone scan Presentation Symptoms insidious onset of pain pain with stairs, inclines, and impact pain common in anterior hip Physical exam mostly normal initially advanced stages similar to hip OA (limited motion, particularly internal rotation) Imaging Radiographs recommended views AP hip frog-lateral of hip AP and lateral of contralateral hip classification systems based largely on radiographic findings (see below) MRI highest sensitivity (99%) and specificity (99%) double density appearance T1: dark (low intensity band) T2: focal brightness (marrow edema) order when radiographs negative and osteonecrosis still suspected presence of bone marrow edema on MRI is predicitve of worsening pain and future progression of disease Bone scan Treatment Nonoperative bisphosphonates indicated for precollapse AVN (Ficat stages 0-II) trials have shown that alendronate prevents femoral head collapse in osteonecrosis with subchondral lucency login to view 1 more bullet Operative core decompression with or without bone grafting indications login to view 2 more bullets technique login to view 6 more bullets rotational osteotomy indications login to view 1 more bullet technique login to view 5 more bullets outcomes login to view 2 more bullets curettage and bone grafting through Mont trapdoor technique or Merle D'Aubigne lightbulb technique indications login to view 1 more bullet technique login to view 2 more bullets vascularized free-fibula transfer indications login to view 2 more bullets technique login to view 2 more bullets outcomes login to view 2 more bullets complications login to view 5 more bullets total hip replacement indications login to view 3 more bullets techniques login to view 2 more bullets outcomes login to view 4 more bullets total hip resurfacing indications login to view 3 more bullets outcomes login to view 1 more bullet hip arthrodesis indications login to view 1 more bullet Prognosis Risk of femoral head collapse with osteonecrosis is based on the modified Kerboul combined necrotic angle calculated by adding the arc of the femoral head necrosis on a mid-sagittal and mid-coronal MR image Low-risk group = combined necrotic angle less than 190° Moderate-risk group = combined necrotic angle between 190° and 240° High-risk group = combined necrotic angle of more than 240°