14 Legg–Calvé–Perthes Disease
Articular cartilage changes observed in deep layer of cartilage.
Cessation of endochondral ossification at the articular cartilage–subchondral bone junction.
Changes in the bony epiphysis include the following:
Necrosis of the marrow space and trabecular bone.
Compression fracture of the trabeculae.
Fibrovascular granulation tissue invasion of the necrotic head.
Physeal changes seen most frequently in the anterior femoral head, areas of cartilage extending below the endochondral ossification line.
II. Pathogenesis of femoral head deformity:
Healing potential better in younger children: better outcomes in children younger than 6 years at age of onset compared to older than 8 years. 7
III. Natural history:
Limited by small sample sizes.
Long-term outcomes better in patients with spherical femoral heads. 4
Degree of femoral head deformity at skeletal maturity is associated with onset of osteoarthritis. 8
Highest documented incidence in Northern European invidivuals. 9
Lower incidence among African Americans versus Caucasians. 9
Multiple studies showing variations within regions of the same country. 9
I. Plain radiographs include weight-bearing anteroposterior (AP) and frog leg lateral views of bilateral hips.
II. May be radiographically silent for the first 3 to 6 months. 13
Group A: less than 50% femoral head involvement.
Group B: greater than 50% femoral head involvement.
Group I: 25% involvement—better outcomes.
Group II: 50% involvement—better outcomes.
Group III: 75% involvement—worse outcomes
Group IV: 100% involvement—worse outcomes.
Simplification into groups I and II and III and IV improves interobserver reliability. 17
Group A: normal height.
Group B: less than 50% height loss.
Group B/C: around 50% height loss.
Group C: greater than 50% height loss.
Stulberg’s classification: applied at skeletal maturity to prognosticate long-term outcome 8 :
I: normal hip.
II: spherical head with enlargement, short neck, or steep acetabulum.
III: nonspherical head, aspherically congruent joint.
IV: flat head, aspherically congruent joint.
V: flat head with incongruent joint.
Simplification proposed: groups I and II with spherical heads have good outcomes, while groups III to V with aspherical heads are much more likely to progress to osteoarthritis. 19
The problem with all the radiographic/prognostic classification systems is that they cannot be applied until fragmentation, although this may be changing with proposed modifications to the Waldenstrom classification. 20
In patients requiring treatment, outcomes may be better if initiated prior to fragmentation.
Type A: early and rapid revascularization.
Centrally located activity or absence of activity in the epiphysis after 5 months.
Higher risk of a poor prognosis.
Type C: regression from a type A to a type B, very rare.
Flat or round femoral head.
Degree of extrusion of the femoral head.
Extent of necrosis.
Not accurate enough to describe stages of healing.
When progressive subluxation of the femoral head is suspected, MRI can be used instead of arthrography.
Dynamic gadolinium-enhanced subtraction MRI allows early detection of ischemia and revascularization patterns, excellent agreement with bone scintigraphy to determine favorable prognosis or not.
VI. Arthrography: useful to evaluate coverage and mobility under direct visualization prior to treatment for containment. 13
VII. Ultrasonagraphy 13 :
Likely will show hip effusion.
III. Salter–Thompson size of crescent sign: strong prognostic factor but only present in one-third of plain radiographs. 15
IV. Epiphyseal involvement (Catterall): strong prognostic factor, only moderate reproducibility. 16
V. Lateral pillar involvement: strong prognostic factor, good reproducibility. 18
VI. Metaphyseal abnormalities (osteoporosis, cysts, widening), poor prognostic indicators. 22
VII. Altered acetabular contour (bicompartmentalization), poor prognostic factor. 22
VIII. Catterall’s “head-at-risk” signs 16 :
Diffuse metaphyseal reaction.
Calcification lateral to the epiphysis: questionable.
Gage’s sign: triangular lucent are on the lateral epiphysis.
Horizontal capital femoral epiphysis: questionable.
IX. Femoral epiphyseal extrusion: most important 22 :
Loss of containment.
Predisposes to femoral head deformation.
When more than 20% of the width of the femoral head extrudes, there is high chance of the femoral head becoming deformed.
More pronounced in older children and with more epiphyseal involvement.
Only modifiable factor.
Femoral head asphericity.
Steepness of the acetabular roof.