What is the significance of bilateral acetabular dysplasia?

Significance of Bilateral Acetabular Dysplasia

Bilateral acetabular dysplasia is a serious condition that can lead to premature osteoarthritis, abnormal gait, decreased strength, and may ultimately require total hip arthroplasty in patients under 60 years if left untreated. 1 This condition represents a significant cause of hip-related pain in young and middle-aged adults that requires prompt diagnosis and management.

Clinical Significance and Pathophysiology

Acetabular dysplasia refers to misalignment between the femoral head and the acetabulum due to changes in their shape, size, and orientation, which results in:

• Instability and overload of the acetabular rim during normal activities 2
• Increased mechanical stress on the cartilage matrix with eventual failure of the acetabular labrum 3
• Progressive joint degeneration leading to early-onset osteoarthritis 4

In bilateral cases, both hips are affected, potentially causing more significant functional impairment than unilateral cases.

Radiographic Features

The primary radiographic findings in acetabular dysplasia include:

• Vertically oriented acetabular roof 2
• Decreased center-edge angle (typically less than 20°) 4
• Increased acetabular angle and acetabular roof angle 5
• Increased head lateralization index 4
• Possible presence of an "os acetabuli" (bone fragment separated from the acetabular rim) 6

The severity of femoral head deformity often correlates with the degree of acetabular dysplasia, with significant correlations between the roundness index and other dysplasia parameters 5.

Clinical Presentation

Patients with bilateral acetabular dysplasia typically present with:

• Hip-related pain, often felt in the groin but may also be experienced in the back, buttock, or thigh 2
• Limitation of hip abduction (most important clinical sign after 3 months of age) 1
• Asymmetrical hip creases in infants 1
• Abnormal gait pattern 1
• Decreased strength and function 1

Diagnostic Approach

Diagnosis requires a combination of clinical examination and imaging:

1. Clinical examination:

   • Limitation of hip abduction test (most important clinical sign after 3 months of age) 1
   • Ortolani and Barlow tests in infants 1
   • Assessment for asymmetry of thigh or gluteal folds 1
   • Evaluation for leg length discrepancy (Galeazzi sign) 1

2. Imaging:

   • For infants 0-4 weeks: Clinical examination only 1
   • For infants 4 weeks-4 months: Ultrasound of the hips 1
   • For patients >4 months: Pelvic radiography with anteroposterior view in neutral position, frog-leg view, and Von Rosen view 1
   • Advanced imaging (CT/MRI) may be needed to assess the 3D nature of the deformity 7

Classification

Recent advances suggest that acetabular dysplasia should be understood as a 3D deformity with multiple patterns of instability 7:

1. Anterior instability
2. Posterior instability
3. Global instability

This classification helps guide appropriate surgical management through targeted acetabular reorientation 7.

Treatment Options

Treatment depends on age and severity:

• Infants: Pavlik harness as first-line treatment (70-95% success rate when applied before 6 weeks of age) 1
• Failed harness treatment: Closed reduction with hip spica cast 1
• Young adults with pre-OA or early-stage OA: Rotational acetabular osteotomy or periacetabular osteotomy 4
• Advanced OA: Total hip replacement 3

Long-term Outcomes and Prognosis

The long-term significance of bilateral acetabular dysplasia depends on timely intervention:

• Untreated dysplasia can lead to up to one-third of total hip arthroplasties in patients under 60 years 1
• Rotational acetabular osteotomy for pre-OA and early-stage OA has shown excellent long-term results at 20 years follow-up 4:
  • 96% survival rate at 20 years for pre-OA cases
  • 78% survival rate at 20 years for early-stage OA cases

Risk Factors for Poor Outcomes

Factors associated with poor outcomes include:

• Fair (rather than excellent or good) postoperative joint congruency 4
• Age older than 46 years at the time of surgery 4
• Delayed diagnosis and treatment 1
• Avascular necrosis (most serious complication of treatment) 1

Clinical Pitfalls to Avoid

• Relying solely on 2D imaging for diagnosis, as acetabular dysplasia is a 3D deformity 7
• Delaying diagnosis and treatment, as early intervention provides better outcomes 1, 4
• Excessive abduction or forceful reduction during treatment, which can lead to avascular necrosis 1
• Failing to continue monitoring through skeletal maturity, as complications can develop during growth spurts 1

Bilateral acetabular dysplasia represents a significant clinical challenge that requires careful assessment and appropriate intervention to prevent long-term disability and premature osteoarthritis.