What are the considerations for a total hip replacement (THR) in a patient with a dysplastic hip?

Total Hip Replacement in Dysplastic Hip

For patients with dysplastic hip requiring total hip replacement, reconstruction should place the acetabular component at the anatomic hip center (low and medial) while addressing femoral abnormalities, which may require specialized implants or femoral shortening osteotomy in severe cases. 1

Anatomical Challenges in Dysplastic Hip

Acetabular Abnormalities

• Shallow, elongated acetabulum with deficient bone stock
• Superior and lateral migration of the femoral head
• Decreased acetabular coverage and depth
• Potential for significant bone deficiency 1, 2

Femoral Abnormalities

• Hypoplasia of the femur
• Excessive femoral neck anteversion (forward rotation)
• Valgus neck-shaft angle
• Metaphyseal-diaphyseal mismatch
• Posteriorly displaced greater trochanter
• Narrowed femoral canal 3

Preoperative Planning

Imaging Requirements

• Standard radiographs (AP pelvis, lateral hip)
• CT scan to assess:
  • Acetabular bone stock
  • Femoral version
  • Leg length discrepancy
  • Three-dimensional anatomy 1

Classification

Use Crowe classification to guide surgical approach:

• Type I: <50% subluxation
• Type II: 50-75% subluxation
• Type III: 75-100% subluxation
• Type IV: Complete dislocation 2

Surgical Considerations

Acetabular Reconstruction

1. Position the cup at anatomic hip center (low and medial) 1
2. Options for acetabular coverage:
   • Medialization of the component
   • Use of smaller acetabular components
   • Lateral bone grafting for severe deficiency
   • Augmentation with autograft from femoral head 2, 4
3. Component selection:
   • Uncemented porous-coated hemispherical components preferred
   • Supplemental screw fixation often necessary
   • Avoid oversizing the acetabular component 1, 4

Femoral Reconstruction

1. Standard stems for mild dysplasia (Crowe I-II)
2. Specialized implants for moderate dysplasia with:
   • Modularity to address version issues
   • Smaller sizes to accommodate narrow canals
   • Options to decouple metaphyseal fit from stem version 1, 3
3. Femoral shortening osteotomy for severe dysplasia (Crowe III-IV):
   • Subtrochanteric shortening osteotomy
   • Metaphyseal resection with greater trochanteric osteotomy and advancement 5, 1

Potential Complications

Specific to Dysplastic Hip THR

• Nerve injury (particularly sciatic) due to limb lengthening
• Instability due to abductor insufficiency
• Component malposition
• Leg length discrepancy
• Higher rates of mechanical failure compared to primary THR 1, 2

General THR Complications

• Infection (19.3% of revisions)
• Instability/dislocation (17.4% of revisions)
• Aseptic loosening (15.8% of revisions)
• Periprosthetic fracture
• Venous thromboembolism 6

Postoperative Management

Pain Management

• Multimodal approach including:
  • Paracetamol
  • NSAIDs/COX-2 inhibitors
  • Opioids as rescue medication 7, 6
• Consider regional anesthesia techniques:
  • Single-shot fascia iliaca block or local infiltration analgesia 7

Rehabilitation

• Early mobilization (postoperative day 0-1)
• Focus on weight-bearing exercises and hip abductor strengthening
• Careful progression to avoid complications from excessive early loading 6

Outcomes

The results of total hip arthroplasty in dysplastic hips demonstrate high rates of pain relief and functional improvement. However, long-term durability of cemented total hip arthroplasty in these patients is inferior to that in the general population. Uncemented implants show promising results, but only limited early and midterm data are available 5.

When performed with proper technique and attention to the unique anatomical challenges, THR can yield excellent results in this complex patient population 1.