Adult Developmental Dysplasia of the Hip

Typical Deformities

Acetabulum

Primary deformity in hip dysplasia is the acetabulum:

1. Lateralised

2. Shallow

3. Retroverted

4. Deficient anteriorly and superiorly

Femur

  1. Valgus neck
  2. Anteverted neck
  3. Small head
  4. Posterior greater trochanter (GT)
  5. Narrow canal
  6. Shortened leg

Consequences

  • Lateralised centre of rotation
  • Increased body weight lever arm
  • High contact pressures
  • Premature osteoarthritis (OA)
  • Tendency for superolateral migration

Assessment

History

  • Previous surgeries
  • Impingement symptoms
  • Family history
  • Childhood history

Examination

  • Signs of impingement
  • Leg lengths
  • Range of motion (ROM)
  • Other deformities (e.g., spine)

X-Ray (XR)

  • Lateral CE angle:
    Normally > 25 degrees; <20 means a dysplastic acetabulum
  • Anterior CE angle:
    Should be >25 degrees (anteverted)
  • Acetabular index
  • Crossover sign:
    Indicates retroverted acetabulum
  • Tönnis Angle:
    Top of femoral head and slope of acetabular roof should be <15 degrees

CT Scan

  • Useful in planning treatment (e.g., osteotomy)

Classification - Crowe and Tönnis Grades

Crowe Classification

Based on the ratio of the distance between the inter-teardrop line and the head-neck junction with the opposite femoral head diameter. If the opposite femoral head is deformed, substitute 20% of pelvic height.

  • Type 1: <50% proximal migration
  • Type 2: 50-75% proximal migration
  • Type 3: 75-100% proximal migration
  • Type 4: >100% proximal migration

Management

Non-Arthroplasty Options

Aim is to resolve pain and slow progression of OA:

1. Analgesia and activity modification

2. Arthroscopy

3. Periacetabular osteotomy

4. Femoral osteotomy

5. Arthrodesis

6. Resection arthroplasty

Arthroscopy and Labral Debridement

  • Indicated for Crowe type 1 with minimal acetabular or femoral deformity
  • Results poor if bony deformities are left uncorrected

Pelvic Osteotomy – Corrective or Salvage

Aims to provide a congruent joint with femoral head coverage and redistribute contact pressures.

  • Corrective Osteotomy:
    • For mild to moderate dysplasia with minimal OA
    • Preferred over femoral osteotomy as acetabulum is the primary problem
    • Bernese Periacetabular Osteotomy:
      • Large corrections possible
      • Extra-articular
      • Single incision
      • Good results by multiple authors
    • Other corrective osteotomies:
      • Salter: For children; relies on supple symphysis
      • Triple innominate: Risk of AVN of acetabulum
  • Salvage Osteotomy:
    • Rare due to success of Bernese osteotomy
    • Indicated in severe dysplasia with insurmountable deformity
    • Types: Chiari or Shelf

Femoral Osteotomy

Indicated if:

- Acetabular development in children depends on head reduction

- Predominant femoral deformity and minimal acetabular deformity (rare)

- Coverage of head not achieved with pelvic osteotomy

Arthrodesis

  • Rare; for severe dysplasia, advanced OA, and poor arthroplasty candidates
  • Indications: Cerebral palsy or polio
  • Pain relief at the expense of function; only for unilateral dysplasia

Resection Arthroplasty

  • Indications similar to arthrodesis but for non-ambulatory patients
  • Lower morbidity surgery
  • Complications:
    • Shortening
    • Chronic pain
    • Difficulty ambulating

Arthroplasty in Hip Dysplasia

Aims

  • Restore normal hip centre of rotation
  • Provide adequate acetabular coverage
  • Ensure long-lasting fixation

Potential Problems

Soft Tissue Contracture

  • Hamstrings, adductors, and rectus femoris
  • Abductors are more transverse and less functional
  • Thickened capsule and iliopsoas
  • Shortened sciatic nerve (palsy more common if >4cm lengthening)
  • THR instability

Approach

  • Acetabular exposure is difficult:
    • Consider trochanteric osteotomy
    • Consider subtrochanteric osteotomy if femur needs shortening

Acetabulum

  • Difficult to identify the true acetabulum
  • Small components required due to underdeveloped acetabulum
  • Poor medial bone stock
  • Lateral acetabular erosion (especially in Crowe type 2 and 3 hips)

Options:

  • Superolateral bone grafting
  • High hip centre (undesirable)
  • Medialisation of cup through the medial wall
  • Crowe type 1 and 4 hips usually have good lateral bone

Femur

Deformities include:

- Narrow canal (affects stem selection)

- Posterior GT (may require osteotomy and reattachment)

- Valgus neck (requires low neck cut)

- Anteverted neck (avoid using native femur as a guide to version)

Stem Selection

  • Narrow canal requires small stems
  • DDH stems have reduced metaphyseal flare
  • Uncemented stems preferred in younger patients
  • Modular stems help correct version
  • Risk: Placement in anteversion

Femoral Shortening

  • Necessary for Crowe type 3 and 4:
    • Contractures prevent reduction into the normal hip centre
    • Options:
      • Subtrochanteric osteotomy (better but more difficult)
      • Metaphyseal resection and distalisation of GT (easier but risks non-union)

Results

  • Worse than standard THR due to complexity
  • More complications and younger, active patients
  • Uncemented results generally better
  • Crowe type 1 outcomes are better than type 3 and 4
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