Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

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Hip Avascular Necrosis

Basics
Description
  • AVN is osteonecrosis, or death of the bone.
    • All major joints can be affected.
    • In the pediatric population, this condition is called Legg-Calve-Perthes disease and, in general, has a better prognosis than osteonecrosis in the adult.
  • AVN of the hip is osteonecrosis of the femoral head.
  • Synonyms: Osteonecrosis; Aseptic necrosis; Chandler disease
  • Classification:
    • Ficat and Arlet described 4 stages:
      • Stage I: No changes on radiograph, changes noted on MRI
      • Stage II: Sclerotic or cystic changes on radiographs in the femoral head, no collapse
      • Stage III: Subchondral fracture, crescent sign on radiographs
      • Stage IV: Degenerative changes in the hip joint with involvement of the femoral head
    • Steinberg et al. modification of the Ficat and Arlet classification (all stages except stage 0 + advanced degenerative changes):
      • Stage 0: Normal radiograph, normal bone scan
      • Stage I: Normal radiograph, abnormal bone scan
      • Stage II: Sclerosis or cyst formation in the femoral head (A = mild, <20%; B = moderate, 20-40%; C = severe, >40%)
      • Stage III: Subchondral collapse (crescent sign) without flattening (A = mild, <15%; B = moderate, 15-30%; C = severe, >30%)
      • Stage IV: Flattening of the head without joint narrowing or acetabular involvement (A = mild, <15% of surface and <2 mm of depression; B = moderate, 15-30% of surface or 2-4 mm of depression)
      • Stage V: Flattening of head with joint narrowing or acetabular involvement (A = mild; B = moderate; C = severe [acetabular involvement])
    • One of the most predictive findings on radiography or MRI is the actual size of the lesion.
General Prevention
  • Limited systemic corticosteroid use
  • Avoidance of alcohol abuse
  • Early fixation of femoral neck fractures or reduction of hip dislocations
Epidemiology
  • Most common in young adults 20-40 years old and in children 6-10 years old.
  • The average age of patients with osteonecrosis who require hip arthroplasty is 38 years.
  • The distribution between males and females is equal.
  • Patients with atraumatic osteonecrosis of one hip have a >50% chance of developing osteonecrosis of the contralateral side.
Prevalence
~2.5% of total hip replacements are performed for the diagnosis of AVN.
 
Risk Factors
  • Femoral neck fractures
  • Steroid use
  • Alcohol abuse
  • Hemoglobinopathies (e.g., sickle cell anemia)
  • Clotting abnormalities
  • Dysbarism (bends)
  • Ionizing radiation
  • Pancreatitis
  • Gout
Genetics
A genetic pattern may be related to a clotting disorder with protein S deficiency.
 
Etiology
  • Osteonecrosis is most commonly alcohol-related or induced by incremental and cumulative doses of corticosteroids (90%).
    • Alcohol: The threshold of alcohol ingestion reported to be associated with osteonecrosis is the equivalent of 400 mL or more per week of 100% ethyl alcohol (~3 beers per day).
    • Corticosteroids:
      • A total dose of 2,800 mg of oral prednisone over 4 months significantly increases the risk of bone infarction.
      • Some researchers believe that patients who have idiosyncratic reactions to steroids, with systemic changes such as acute weight gain or moon faces, have an increased risk of developing osteonecrosis.
  • Other causes include:
    • Traumatic injuries such as hip fractures
    • Subclinical clotting disorders
    • Exposure to atmospheric pressure variations
Associated Conditions
  • Hip fracture
  • Hemoglobinopathy
  • Alcohol abuse
  • Perthes disease
Diagnosis
Signs and Symptoms
  • Onset of pain in the hip without antecedent trauma
  • Pain is usually in the groin.
History
  • The patient often initially complains of vague pain in the groin for 4-6 months before evaluation.
  • Pain increases with internal rotation of the hip.
  • A high index of suspicion should exist in a young patient with hip pain and other risk factors.
Physical Exam
  • Look for groin pain with ROM of the hip (internal rotation), which is not typically tender with direct palpation.
  • The patient has a limp but a normal neurologic examination.
  • The combination of history and physical examination should lead to a suspicion of osteonecrosis of the hip.
Tests
Lab
  • Complete blood count
  • ESR
  • Coagulation profile (research tool at present)
Imaging
  • Plain radiographs, including AP and lateral projections of the hip
  • MRI of the hip is the single best test for diagnosing osteonecrosis of the hip (specificity, 98%).
Pathological Findings
  • Although osteonecrosis has many possible causes, a common final pathway leads to the typical pathologic findings, including death of the osteoblast and osteocytes with empty lacunae in the trabecula of the necrotic area.
  • An area of sclerotic margin also commonly is present in the area of necrosis.
Differential Diagnosis
  • Fracture
  • Infection
  • Transient osteoporosis of the hip
  • Neurogenic pain
  • Sports hernia
  • Acetabular labral tear
  • Psoas bursitis
  • Synovitis or adhesions of the capsule
Treatment
General Measures
  • The diagnosis of osteonecrosis of the hip should be made as early as possible.
  • Other joints, including the contralateral hip, knees, shoulders, and ankles, should be evaluated.
  • Patients with this diagnosis should be evaluated by an orthopaedic surgeon who is experienced in treating osteonecrosis of the hip.
  • Nonoperative treatment typically is not successful for symptomatic lesions.
    • The failure rate is ~80%, depending on the size and classification of the lesion.
  • Small lesions have a higher rate of spontaneous resolution than do large lesions.
Special Therapy
Physical Therapy
Physical therapy can be useful for maintaining ROM but usually is of little benefit.
 
Medication
First Line
  • Anticoagulants, antihypertensives, and lipid-lowering agents are all being investigated for the treatment of early-stage disease.
  • Currently, use of these pharmacologic agents should be considered experimental.
  • Evidence exists that diphosphonate may be helpful in preventing collapse.
Surgery
  • Surgery for the treatment of osteonecrosis of the hip can be divided into procedures that preserve the femoral head and arthroplasty options.
  • Head-preserving techniques:
    • Core decompression:
      • Indicated for small- to medium-sized precollapse lesions
      • Weightbearing should be protected for 5 weeks after surgery to avoid fracture.
      • Variable satisfactory outcomes have been reported (range, 40-90%).
    • Osteotomy: Rotates the affected area of the head away from the weightbearing portion.
    • Vascularized fibular grafts: 1 study indicated an 83% success at 17-year follow-up in specialized centers.
    • Nonvascularized bone-graft:
      • Dead bone is removed and replaced with bone graft through a trapdoor in the femoral neck.
      • Reported success rate of 80-83% at 2.5-5 years follow-up
  • Arthroplasty options:
    • Resurfacing arthroplasty:
      • Indicated for patients with severe femoral head collapse and minimal acetabular changes
      • Variable results have been reported.
    • Total hip arthroplasty:
      • Indicated for patients with femoral head collapse and acetabular involvement
      • A lower success rate is reported for patients with osteonecrosis than patients with osteoarthritis.
Follow-up
Prognosis
  • <50% of asymptomatic hips progress to end-stage disease requiring hip arthroplasty.
  • Nonoperative treatment of symptomatic lesions result in 79% failure rate.
  • Patients with diagnoses or risk factors thought to contribute to the development of osteonecrosis have worse outcomes with head-preserving procedures.
Complications
  • Progressive collapse of the hip can lead to debilitating arthritis and the need for total hip arthroplasties.
  • Risk of fracture exists with weightbearing after core decompression.
    • Risk is increased if the core tract is made through diaphyseal bone.
  • Risk of donor site morbidity exists with vascularized fibular grafting.
  • Hip arthroplasty in patients with osteonecrosis has a higher failure rate, owing to loosening, than in patients with osteoarthritis (20% versus 5%, respectively, at 10 years).
    • With modern implants, bearing surfaces may become the limiting factor of replacements in younger patients.
Patient Monitoring
  • Serial radiographs are used to note any progression of joint involvement every 3-4 months.
  • Clinical symptoms are equally important, especially if nonoperative management is selected with the end point of total hip arthroplasty.
Miscellaneous
Codes
ICD9-CM
733.42 Osteonecrosis (aseptic necrosis), femoral head
 
Patient Teaching
Patients are counseled on the natural history of the disease and are asked to call the physician’s attention to bone or joint pain.
 
FAQ
Q: Will osteonecrosis of the hip get better?
A: Spontaneous resolution occurs more often in patients with small lesions. Larger lesions and those that have collapsed are unlikely to improve spontaneously.
 
Q: Which patients should have total hip replacement?
Collapse of the femoral head and arthritic changes in the joint are indications for arthroplasty.

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