What is the step by step management approach for a patient with an old hip dislocation and a false acetabulum undergoing total hip replacement (THR) surgery?

Management of Old Hip Dislocation with False Acetabulum Using Total Hip Replacement

Total hip replacement (THR) for patients with old hip dislocation and false acetabulum requires a systematic surgical approach with careful preoperative planning and meticulous technique to ensure optimal outcomes in terms of pain relief, function, and implant longevity.

Preoperative Assessment and Planning

• Radiographic evaluation:

  • Standard AP pelvis and lateral hip views
  • CT scan to assess:
    • Location and quality of true acetabulum
    • Extent of false acetabulum formation
    • Femoral head position and deformity
    • Bone stock availability
    • Leg length discrepancy

• Patient-specific considerations:

  • Age and activity level
  • Bone quality (osteoporosis assessment)
  • Previous surgeries
  • Neurovascular status
  • Soft tissue contractures

Surgical Procedure

Step 1: Patient Positioning and Approach

• Position patient in lateral decubitus position
• Use extended posterolateral approach for adequate exposure
• Consider extensile approaches if significant deformity exists

Step 2: Identification of Anatomical Landmarks

• Identify and protect sciatic nerve (at higher risk due to altered anatomy)
• Locate both false and true acetabulum
• Identify anatomical landmarks for reference (tear drop, ilioischial line)

Step 3: Femoral Head Resection

• Perform neck cut at appropriate level based on preoperative templating
• Remove femoral head to improve visualization
• Release contracted soft tissues as needed

Step 4: Acetabular Preparation

• Clear soft tissue from true acetabulum
• Identify true acetabular floor
• Progressively ream the true acetabulum to achieve bleeding bone
• Avoid excessive medialization
• Consider bone grafting if significant bone deficiency exists

Step 5: Acetabular Component Placement

• Use cemented femoral stems as recommended by AAOS guidelines for hip fracture patients 1
• Position cup at anatomic hip center when possible
• Aim for 40-45° inclination and 15-20° anteversion
• Options based on bone deficiency:
  • Medialization technique
  • High hip center placement
  • Structural bone grafting (preferred for younger patients)

Step 6: Femoral Preparation and Component Insertion

• Identify femoral canal
• Sequential reaming and broaching
• Address any femoral deformity
• Insert cemented stem with appropriate version (typically 10-15° anteversion)
• Consider modular stems if significant deformity exists

Step 7: Trial Reduction and Stability Testing

• Perform trial reduction with provisional components
• Assess stability through full range of motion
• Check leg length and offset
• Ensure adequate soft tissue tension

Step 8: Final Component Implantation

• Insert final acetabular component with appropriate bone graft if needed
• Insert final femoral component
• Secure final bearing surface
• Perform final reduction

Step 9: Closure

• Repair capsule if possible
• Repair external rotators
• Close wound in layers with meticulous hemostasis

Postoperative Management

Immediate Postoperative Care

• Administer appropriate thromboprophylaxis:
  • Low Molecular Weight Heparin (LMWH) 12-24 hours after surgery
  • Standard duration of 10-14 days, with extended prophylaxis up to 35 days 2
• Multimodal pain management
• Antibiotics for 24 hours
• Monitor for neurovascular complications

Rehabilitation Protocol

• Protected weight-bearing for 6-12 weeks if bone grafting was performed
• Full weight-bearing as tolerated if stable construct without grafting
• Hip precautions based on approach and stability
• Progressive physical therapy focusing on:
  • Gait training
  • Range of motion exercises
  • Strengthening of hip abductors

Potential Complications and Management

• Dislocation:

  • Higher risk due to altered anatomy and soft tissue imbalance
  • Consider constrained liners for recurrent cases 3
  • Immobilization in "deck chair position" (45° flexion, 10-20° abduction, neutral rotation) for anterior dislocations 4

• Nerve injury:

  • Careful protection of sciatic nerve during exposure
  • Limited lengthening (< 4 cm) to prevent nerve stretch

• Infection:

  • Prophylactic antibiotics
  • Careful soft tissue handling
  • Consider antibiotic-impregnated cement

• Leg length discrepancy:

  • Preoperative planning crucial
  • Intraoperative assessment
  • May require accepting some discrepancy to ensure stability

Follow-up Protocol

• Clinical and radiographic evaluation at 6 weeks, 3 months, 6 months, 1 year, and annually thereafter
• Monitor for:
  • Component position and fixation
  • Bone graft incorporation if used
  • Progressive radiolucent lines
  • Heterotopic ossification

Special Considerations

• In younger patients, structural bone grafting to restore anatomic hip center is preferred to provide bone stock for potential future revisions 5
• Consider prophylactic measures against heterotopic ossification in high-risk patients 6
• For patients with severe bone deficiency, custom implants or augments may be necessary

This approach to managing old hip dislocations with false acetabulum through THR addresses the complex anatomical challenges while providing the best chance for improved function, pain relief, and long-term implant survival.