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Introduction
  • Also known as avascular necrosis
  • 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
    • 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
  • 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
  • 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° 
Classification

Steinberg Classification (modification of Ficat classification)
Stage
Radiographs
MRI
Images
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 subchdonral 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
    • 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
 
 

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