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Updated: Dec 22 2023

Hip Osteonecrosis

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  • 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
          • coagulation of the intraosseous microcirculation →
          • venous thrombosis →
          • retrograde arterial occlusion →
          • intraosseous hypertension →
          • decreased blood flow to femoral head →
          • AVN of femoral head →
          • chondral fracture and collapse
      • 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%
        • cervicotrochanteric fracture: 25%
        • 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
          • However, other studies have also shown no benefit of preventing collapse with bisphosphonates
    • Operative
      • core decompression with or without bone grafting
        • indications
          • for early AVN, before subchondral collapse occurs
          • reversible etiology
        • technique
          • traditional method
            • drill an 8-10 mm hole through the subchondral necrosis
          • alternative method
            • pass a 3.2 mm pin into the lesion two to three times for decompression
          • relieves intraosseous hypertension equals less pain
          • stimulates a healing response via angiogenesis
      • rotational osteotomy
        • indications
          • only for small lesions (<15%) in which the lesion can be rotated away from a weight bearing surface
        • technique
          • typically performed through intertrochanteric region
          • for medial disease
            • perform varus rotational osteotomy
          • for anterolateral disease
            • perform valgus flexion osteotomy
        • outcomes
          • reported success rate of 60% to 90%, mainly in Japan
          • distorts the femoral head making THA more difficult
      • curettage and bone grafting through Mont trapdoor technique or Merle D'Aubigne lightbulb technique
        • indications
          • preferably pre-collapse
        • technique
          • lightbulb - through the cortex of the femoral neck-head junction to access the necrotic area of the femoral head and place bone graft
          • trapdoor - through articular surface
      • vascularized free-fibula transfer
        • indications
          • for both pre-collapse and collapsed AVN in young patient
          • reversible etiology preferred
        • technique
          • remove the necrotic area with large core hole
          • fibular strut is placed under subchondral bone to help prevent collapse or tamp up small areas of collapse
        • outcomes
          • some centers demonstrating 80% success at 5 to 10-year follow-up
          • less predictable in patients >40
        • complications
          • related to donor site morbidity
            • sensory deficit
            • motor weakness
            • FHL contracture
            • tibial stress fracture from side graft is taken
      • total hip replacement
        • indications
          • younger patient with crescent sign or more advanced femoral head collapse, +/- acetabular DJD
          • irreversible etiology (chronic steroid use)
          • patients >40 with large lesions
        • techniques
          • cementless cup and stem
          • care must be taken while preparing the femur as there are high rates of femoral canal perforation
        • outcomes
          • in young patients with osteonecrosis, there is a higher rate of linear wear of the polyethylene liner and a higher rate of osteolysis than compared to older patients who have THA for osteoarthritis
          • provides good pain relief and function
          • most reliable means to provide pain relief and immediate return of function
      • total hip resurfacing
        • indications
          • in advanced DJD with small, isolated focus of AVN
          • requires adequate bone to support resurfacing component
          • contraindicated in underlying disease process or chronic steroid use causing AVN (poor bone quality) and renal disease (metal ions from metal-on-metal implant)
        • outcomes
          • medium-term follow-up showing problems with acetabular erosion and pain
      • hip arthrodesis
        • indications
          • only consider in the very young patient in a labor intensive occupation
  • 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°
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