CIM Case: Perthes Disease

Clinical Scenario

Patient: 6-year-old boy Presentation: 3-month history of progressive limp and intermittent left hip pain, referred to groin and anterior thigh, worse with activity Relevant history: No trauma, no recent illness, previously active and healthy, pain sometimes wakes him at night, no fever, no weight loss Examination findings:

• Antalgic gait with shortened stance phase on left
• Left leg held in slight flexion and external rotation
• Reduced hip flexion (100° vs 130°), limited internal rotation (10° vs 40°), limited abduction (20° vs 45°)
• Positive log roll test (pain with rotation)
• No leg length discrepancy currently
• Trendelenburg negative
• No muscle wasting
• Knee examination normal bilaterally

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Investigations Provided

Laboratory Results

Imaging

Image 1: AP Pelvis and Frog-leg Lateral Radiographs

Radiological features:

• Left femoral epiphysis smaller and denser than right (sclerosis)
• Widening of medial joint space (lateral subluxation)
• Crescent sign visible on lateral (subchondral fracture)
• Metaphyseal lucency present
• Physis appears horizontal
• Lateral pillar involvement - partial collapse (Herring B)
• Catterall Group III (50-75% head involvement)

Image 2: MRI of Pelvis (if obtained)

MRI findings:

• Low signal on T1 in anterolateral femoral epiphysis
• High signal on T2/STIR indicating oedema and revascularisation
• Extent of necrosis more clearly defined
• No physeal bar
• Labral changes minimal

Questions & Model Answers

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Key Teaching Points

Pattern Recognition

This pattern suggests Perthes Disease:

• School-age boy (4-8 years) with insidious limp
• Groin/thigh pain worse with activity
• Limited internal rotation and abduction
• Radiographs: small, dense, fragmented femoral head

Distinguish from Transient Synovitis:

Critical Management Points

1. Age is the most important prognostic factor - younger is better
2. Herring classification at fragmentation - determines treatment and prognosis
3. ROM must be restored before surgery - stiff hip cannot be contained
4. Disease is self-limiting - treatment optimises outcome, doesn't cure
5. Head-at-risk signs indicate need for containment - lateral subluxation, Gage sign
6. Long-term OA depends on Stulberg class - aspherical heads fare poorly

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Common Examiner Follow-ups

Q: "When would you do an MRI?"

MRI indications in Perthes:

• Early diagnosis: X-ray equivocal but clinical suspicion high
• Extent of necrosis: Planning treatment, assessing lateral pillar
• Atypical presentation: Exclude other pathology (tumour, infection)
• Bilateral involvement: Consider MED or other skeletal dysplasia
• Poor response to treatment: Assess for complications

MRI provides earlier detection than X-ray and better defines extent of involvement.

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Q: "This child is 9 years old with Herring C. What would you do?"

This is a "bad" Perthes with poor prognosis regardless of treatment:

• Expectation setting: Counsel family about likely outcome (Stulberg IV-V)
• ROM maintenance: Priority is preventing stiff hip
• Containment role limited: Evidence does not show containment helps Herring C at this age
• Observe: Serial X-rays, physiotherapy, activity modification
• Salvage surgery later if needed: Shelf acetabuloplasty, Chiari osteotomy, valgus osteotomy for hinge abduction, or eventual hip replacement

Surgery for poor prognosis Perthes is controversial - may not change outcome.

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Q: "What is the evidence for containment surgery?"

Key evidence:

• Herring Prospective Study (2004, JBJS):
  • Age >8 with Herring B/C: surgical containment better than non-operative
  • Age <8 or Herring A: no benefit from surgery
• Systematic reviews: Weak evidence overall, no clear superiority of one surgical method
• Recent trends: Moving away from bracing, selective surgery based on age and classification

Bottom line: Surgery helps selected patients (older children with Herring B) but doesn't change outcome for very good or very poor prognosis groups.

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Q: "What if this child has bilateral involvement?"

Bilateral Perthes (~10-12%):

• Usually asynchronous (different stages)
• Treat each hip according to its stage and classification
• If synchronous and symmetrical - consider MED or other skeletal dysplasia
• Order lateral spine X-ray (vertebral changes in MED)
• Consider genetics referral

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Related Topics

• Developmental Dysplasia of the Hip
• Slipped Upper Femoral Epiphysis
• Transient Synovitis
• Paediatric Hip Fractures
• Proximal Femoral Osteotomy
• Pelvic Osteotomies