Perthes

Perthes Disease

Epidemiology

  • More common in boys than girls.
  • Typically affects children aged 4-8 years, with an age range of 2-15 years.
  • Predominantly affects White or Asian populations.
  • Often occurs in thin, small, skeletally immature children.
  • Bilateral involvement occurs in 10% of cases but is never concurrent.

Aetiology

  • Idiopathic avascular necrosis (AVN) of the proximal femoral epiphysis.
  • Some children may have an underlying coagulopathy.
  • Theories include:
    1. Repeated ischemic episodes.
    2. Increased hydrostatic pressure due to venous congestion.
    3. Association with fibrinolytic coagulopathy (currently favored theory).

Clinical Presentation

  • Symptoms include a limp, hip or knee pain, and stiffness.

Investigation

  • Blood tests if an abnormal condition is suspected.
  • Plain X-ray usually sufficient.
  • MRI can provide early diagnosis but does not impact management or outcome.

Differential Diagnosis

Unilateral 1. Infection 2. Sickle cell infarct 3. Synovitis, inflammatory arthritis 4. Traumatic causes

Bilateral 1. Spondyloepiphyseal Dysplasia (SED) 2. Multiple Epiphyseal Dysplasia (MED) 3. Gaucher’s Disease 4. Hypothyroidism

Stages of Disease

  1. Necrotic (Initial) (6 months)
    • AVN is evident but no collapse.
    • Signs include the crescent sign (Caffey’s sign) and sclerosis.
  2. Fragmentation (Resorption) (6 months)
    • Femoral head fragmentation, primarily of the lateral epiphysis.
    • Damage occurs, and it is too late to alter the disease course.
  3. Re-Ossification (Healing) (18 months)
    • Bone resorption and re-ossification of the femoral head.
  4. Remodeling (Residual) (3 years)
    • Femoral head fully remodels, with residual Perthes deformities.

Classification

Herring’s Lateral Pillar Classification - Considered the best prognostic indicator and offers good inter- and intra-observer reliability. Outcome worsens with increasing grade.

Group Description
A Lateral pillar height is normal
B Lateral pillar height >50%
B/C Lateral pillar height 50% with a narrowed physis
C Lateral pillar height <50%

Catteral Head-at-Risk Signs - Associated with a worse prognosis: - Gage Sign: Triangular lucency on the lateral physis. - Horizontal orientation of physis. - Lateral Subluxation of the femoral head (most important). - Calcification lateral to the physis. - Metaphyseal cysts.

Reimer’s Migration Index - Indicates the degree of femoral head extrusion, useful for assessing when intervention is necessary.

Problems with Classification

  • Best intervention time is before collapse and extrusion.
  • Existing classifications focus on the degree of collapse, making it too late to change the disease’s natural course.
  • No classifications directly address femoral head extrusion, the most significant alterable factor surgically.

Prognostic Factors

Factor Prognosis
Age <5 years: generally good prognosis with high remodeling potential
Degree of Extrusion >20% extrusion associated with poor prognosis
Hip Stiffness Poor prognosis with stiff hips, regardless of treatment
Gender Girls tend to have worse outcomes due to shorter remodeling time

Management

Head Deformation in Perthes & Containment Rationale

  • Head deformation, which occurs in the late fragmentation or early re-ossification phase, is the primary issue.
    • Leads to coxa magna, trochanteric overgrowth, hip impingement, and early osteoarthritis.
    • Deformation also causes premature physeal arrest and neck shortening, which results in Trendelenburg gait.

Prevention Strategy: Prevent lateral extrusion of the epiphysis through containment to avoid deformation.

Non-Operative Management

  • Focus on maintaining range of motion (ROM).
  • Avoid sports but allow weight-bearing.
  • Close follow-up to monitor for extrusion.
  • Approximately 60% of children manage without surgery.

Factors for Surgical Containment

  • Age: Low threshold for surgery in children >8 years due to the likelihood of extrusion.
  • Timing: Containment is only effective in the initial or fragmentation stages.
  • Hip Stiffness: Poor outcomes with surgery if the hip is stiff; pre-operative traction may improve ROM.

Femoral (VDRO) vs. Pelvic Osteotomy - Femoral osteotomy is generally more effective and simpler. - Pelvic osteotomy is reserved for salvage procedures.

Trochanteric Advancement or Epiphysiodesis - Prevents trochanteric overgrowth and Trendelenburg gait. - Suitable for older children with limited femoral head remodeling potential.

Management by Age

Age Range Management Strategy
Under 5 years Observe if no extrusion; use abduction brace if extrusion is present
5-8 years Watch if no extrusion; perform VDRO if extrusion is present
>8 years Aggressive treatment recommended due to poor prognosis
Late Presentation with Deformity Options include trochanteric advancement, Chiari/shelf osteotomy, valgus osteotomy, cam excision, or hip fusion (convertible to THR later)

Long-Term Outcome

  • Few symptoms under 40 years of age, but most individuals over 40 years with Perthes disease develop symptoms.
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