Summary

Perthes Disease is an idiopathic Avascular Necrosis (AVN) of the capital femoral epiphysis in children (typically boys aged 4-8). It is a self-limiting condition with four distinct radiological stages (Waldenström): Initial, Fragmentation, Re-ossification, and Healed. The prognosis is primarily determined by the Age of Onset (<6 years is good) and the Extent of Necrosis (Herring Lateral Pillar Classification). Management relies on the principle of "Containment"—keeping the soft, biological "plasticine" femoral head inside the spherical mould of the acetabulum to prevent flattening (Coxa Plana). [1,2,3]

Key Facts

• Demographics: Male:Female = 4:1. Age 4-8.
• The "Head at Risk": Signs that predict poor outcome (Gage sign, Lateral calcification, Lateral subluxation).
• Bilateral?: 10-15% are bilateral, but usually asynchronous (one hip starts after the other). If occurring simultaneously, suspect Multiple Epiphyseal Dysplasia or Hypothyroidism.

Clinical Pearls

"The Painless Limp": The classic presentation is an intermittent limp that worsens with activity. Pain is often mild and referred to the Knee (Obturator nerve). Always examine the hip in a child with knee pain!

"6 is the Magic Number": Children under 6 years almost always do well without surgery because they have huge biological potential to remodel. Children over 8 do poorly because they have less time before skeletal maturity.

"Abduction is Key": Loss of abduction is the first sign of "Hinge Abduction" (the head is no longer round and catches on the socket).

1. Gait Analysis

• Watch them run. The limp often becomes more obvious.

2. Range of Motion

• Prone Internal Rotation: The most sensitive test. Patient lies on front, knees bent 90 degrees. Rotate feet outwards. The affected side will have significantly restricted internal rotation.

3. Trendelenburg Test

• Stand on one leg. The pelvis drops on the unaffected side (due to weakness of abductors on the standing/affected leg).

X-Ray (AP and Frog-Leg Lateral)

• Herring Lateral Pillar Classification (The Gold Standard):
  • Based on the height of the Lateral Pillar (the outer 1/3 of the femoral head) during the fragmentation stage.
  • Group A: No loss of height. (Good outcome).
  • Group B: <50% loss of height.
  • Group C: >50% loss of height. (Poor outcome - the "tent pole" has collapsed).
• Catterall Classification (Historical): Based on head involvement (I-IV). Less reproducible than Herring.

MRI

• Used in the "Initial" stage if X-rays are normal but suspicion is high. Shows marrow edema and loss of perfusion.

"Head at Risk" Signs (Catterall)

• Predict poor outcome:
  1. Gage Sign: A V-shaped defect in the lateral epiphysis.
  2. Calcification: Lateral to the epiphysis.
  3. Lateral Subluxation: The head slipping out.
  4. Horizontal Physis: Growth plate angle changes.
  5. Metaphyseal Cysts.

                 PERTHES DIAGNOSIS
                        ↓
                 AGE AT ONSET?
          ┌─────────────┴─────────────┐
      < 6 YEARS                   > 6 YEARS
          ↓                           ↓
     OBSERVATION              LATERAL PILLAR?
    (Physio/Rest)             ┌───────┴───────┐
                              A               B/C
                              ↓               ↓
                           OBSERVE      CONTAINMENT SURGERY
                                      (Pelvic/Femoral Osteotomy)

Principles (The "Containment" Concept)

The acetabulum acts as a spherical mold. The femoral head is soft (fragmenting). If we keep the head deeply inside the socket while it moves, it will heal round. If it subluxes, it will heal flat (Mushroom shape).

Methods

1. Observation: For age <6 or Herring A.
2. Physiotherapy: Maintain Abduction and Internal rotation. Hydrotherapy.
3. Activity Modification: Avoid impact sports (trampoline, jumping) during fragmentation stage (12-18 months).
4. Bracing (Toronto/Scottish Rite): Historically used to hold legs in abduction. Evidence suggests it is ineffective and socially stigmatizing. Mostly abandoned.

Indications

• Age > 6 years (onset).
• Herring B or C.
• "Head at Risk" signs.
• Loss of containment (Subluxation).

1. Femoral Varus Osteotomy (VDRO)

• Technique: Cut the femur and tilt the neck downwards (Varus).
• Effect: Points the head deeper into the socket.
• Pro: Addresses the femur directly.
• Con: Shortens the leg, causes limp (abductor weakness).

2. Pelvic Osteotomy (Salter / Triple)

• Technique: Cut the pelvis and rotate the acetabulum over the head.
• Effect: Better coverage (roof).
• Pro: Does not shorten the leg.
• Con: bigger surgery.

3. Shelf Acetabuloplasty

• Technique: Adding a bone graft "shelf" to the edge of the socket to extend it if the head is extruded. Salvage procedure.

Stulberg Classification (Final Outcome)

• Assessed at skeletal maturity.
• Class I/II: Spherical head. Good joint.
• Class III/IV: Ovoid/Flat head (Coxa Plana). Mismatch.
• Class V: Congruent but flat.
• Consequence: Class III-V leads to early osteoarthritis (age 40-50).

Long Term

• Most patients do well until 40s.
• Early Total Hip Replacement is the endpoint for severe deformities.

Herring et al (2004) - The Definitive Study

• Multicenter prospective study.
• Findings:
  • Age < 8 + Herring B/C: Surgery (Osteotomy) had significantly better outcomes than non-op.
  • Age > 8 + Herring B/C: Outcomes were poor regardless of treatment (Salvage only).
  • Herring A: Did well regardless of treatment.

British Orthopaedic Association (BOA)

• "Children < 6 years require symptomatic treatment only unless there is clinical/radiological evidence of progressive head deformity or subluxation."

What is Perthes?

The blood supply to the ball of the hip joint has temporarily stopped. This causes the bone to soften and crumble, like a biscuit in tea.

Will it heal?

Yes. The blood supply always comes back. The bone will regrow. The process takes 2-3 years.

What is the risk?

While the bone is soft, it can get squashed flat ("Mushroom shape"). A flat ball doesn't roll well in a round socket, which causes stiffness and arthritis later in life. Our goal is to keep the ball round while it regrows.

Does my child need surgery?

It depends on their age. Young children (<6) heal very well and rarely need surgery. Older children (>8) heal less well and often need operations to guide the bone into the right shape.

Q1: What are the 4 radiological stages of Perthes (Waldenström)? A: 1. Initial (Necrosis). 2. Fragmentation (Resorption). 3. Re-ossification (New bone). 4. Healed (Remodelling).

Q2: Describe the "Gage Sign". A: A radiolucent 'V' shaped defect in the lateral part of the epiphysis. It is a "Head at Risk" sign indicating potential for lateral extrusion.

Q3: Why is Age the most important prognostic factor? A: Younger children have a longer period of remodeling remaining before skeletal maturity. They also have a thicker cartilage cartilage model which protects the spherical shape. The cutoff is generally 6 years.

Q4: Differentiate Perthes from SUFE clinically. A: Perthes: Younger (4-8), Painless Limp, Loss of Abduction/Int. Rotation. SUFE: Older (10-14), Painful groin/knee, Leg lies effectively Externally Rotated.

(End of Topic)