What is the management approach for a patient with osteonecrosis of the hip in a small area?

Management of Osteonecrosis of the Hip in a Small Area

For small area osteonecrosis of the hip (<30% of femoral head volume), observation with regular monitoring is recommended as the initial approach, as these lesions have <5% risk of progression to collapse, while considering core decompression only if symptoms develop. 1, 2

Diagnosis and Assessment

• Initial evaluation should include plain radiographs (anteroposterior and frog-leg lateral views) to exclude other causes of hip pain such as fracture, primary arthritis, or tumor 1
• MRI without contrast is the gold standard for confirming diagnosis, determining the size of the lesion, and staging the disease 1
• The necrotic volume is the most critical prognostic factor - lesions involving <30% of the femoral head have <5% progression to collapse, compared to 46-83% progression rate for lesions >30% 1, 2
• Additional risk factors for progression include: increased joint effusion, bone marrow edema, patient age >40 years, and BMI >24 kg/m² 1

Management Approach Based on Lesion Size

For Small Lesions (<30% of femoral head)

• Observation with regular monitoring is appropriate for asymptomatic small lesions 2, 3

• Conservative measures include:

  • Weight-bearing restriction (not effective alone but may be useful when combined with other treatments) 4, 5
  • Regular individualized exercise regimen including strengthening exercises for both legs, especially quadriceps and hip girdle muscles 1
  • Appropriate footwear and consideration of walking aids to reduce pain 1
  • Weight loss if overweight or obese 1

• Pharmacological options with limited supporting evidence include:

  • Bisphosphonates (may decrease pain and rate of bone necrosis in early stages) 4, 5
  • Statins (may have protective effects, especially in steroid-induced cases) 4, 6
  • Anticoagulants such as enoxaparin (may curb disease progression in early stages) 4, 5

• Biophysical modalities with limited evidence include:

  • Extracorporeal shock wave therapy 4, 5
  • Hyperbaric oxygen 4, 5
  • Pulsed electromagnetic field therapy 4, 5

For Symptomatic Small Lesions

• Core decompression may be considered for symptomatic small lesions to prevent articular collapse 1, 7
• Core decompression can be supplemented with:
  • Injection of autologous bone marrow cells 1, 2
  • Vascular fibular grafting 1, 2
  • Electric stimulation 1, 2
• Postoperative protected weight-bearing is recommended following core decompression 7, 8

Important Considerations and Pitfalls

• Prophylactic core decompression for asymptomatic small lesions is controversial and may not change the natural history of the disease 9, 6
• A study following asymptomatic very small lesions (<5 cm³, <10% of femoral head) for 11 years found that 88% eventually became symptomatic and 73% demonstrated collapse, suggesting the need for long-term monitoring even with small lesions 3
• Femoral head osteonecrosis is often bilateral (70-80%) in nontraumatic cases, requiring evaluation of both hips 1, 2
• Regular follow-up with radiographic evaluation is essential to monitor for disease progression, as symptoms typically precede collapse by at least 6 months 7, 3
• For lesions that progress to collapse (late-stage), resurfacing hemiarthroplasty or total hip arthroplasty is recommended 1, 2

Follow-up Protocol

• Regular clinical and radiographic follow-up every 3-6 months is recommended for small asymptomatic lesions 7, 3
• Multiple radiographic views may be required to demonstrate small areas of collapse 3
• Consider CT imaging if collapse is suspected but not visible on plain radiographs 7, 8