14 Legg–Calvé–Perthes Disease

Brian D. Lewis, Robert C. Kollmorgen

14 Legg–Calvé–Perthes Disease

Introduction

I. Pathophysiology:
1. Generally accepted that disruption of the vascular supply to the femoral head is the key pathogenic event. ¹ , ² , ³
2. Pathologic processes affect articular cartilage and the osseous epiphysis and, in some patients, the metaphysis and the physis ⁴ , ⁵ :
  1. Articular cartilage changes observed in deep layer of cartilage.
  2. Cessation of endochondral ossification at the articular cartilage–subchondral bone junction.
  3. Changes in the bony epiphysis include the following:
    1. Necrosis of the marrow space and trabecular bone.
    2. Compression fracture of the trabeculae.
    3. Osteoclastic resorption.
    4. Fibrovascular granulation tissue invasion of the necrotic head.
  4. 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:
1. Mechanical: femoral head begins to deform when forces applied are greater than the ability to resist deformation. ⁴ , ⁶
2. 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:
1. Limited by small sample sizes.
2. Long-term outcomes better in patients with spherical femoral heads. ⁴
3. Degree of femoral head deformity at skeletal maturity is associated with onset of osteoarthritis. ⁸
IV. Epidemiology:
1. Males are five times more likely to be affected. ⁵ , ⁹
2. Highest documented incidence in Northern European invidivuals. ⁹
3. Lower incidence among African Americans versus Caucasians. ⁹
4. Multiple studies showing variations within regions of the same country. ⁹
5. Significant variation even found within small areas (variations between children in different social classes within Merseyside, UK). ⁹ – ¹¹
6. Variation patterns indicate environmental influence on cause of disease. ⁹ , ¹²

Imaging

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
III. Classifications:
1. Waldenstrom’s classification: defines stages, no prognosis ⁴ , ¹⁴ ( Fig. 14.1 ):
  1. Initial stage.
  2. Fragmentation stage.
  3. Reossification stage.
  4. Residual stage.
2. Salter–Thompson classification: prognostic based on extent of subchondral fracture (crescent sign) ⁴ , ¹⁵ :
  1. Group A: less than 50% femoral head involvement.
  2. Group B: greater than 50% femoral head involvement.
3. Catterall’s classification: prognostic based on extent of epiphyseal involvement, recognized during the fragmentation stage ¹³ , ¹⁶ ( Fig. 14.2 ).
  1. Group I: 25% involvement—better outcomes.
  2. Group II: 50% involvement—better outcomes.
    
    Fig. 14.1 Waldenstrom chronological stages of Perthes: I, sclerosis of epiphysis; II, fragmentation; III, early healing; IV, complete healing. (Source: Femoral Neck Fractures, In: Mullis B, Gaski G, eds. Synopsis of Orthopaedic Trauma Management. New York, NY:. Thieme; 2020.)
  3. Group III: 75% involvement—worse outcomes
  4. Group IV: 100% involvement—worse outcomes.
  5. Simplification into groups I and II and III and IV improves interobserver reliability. ¹⁷
4. Lateral pillar classification: based on the femoral head of the lateral pillar (the lateral 15–30%) radiolucency during fragmentation ¹⁸ ( Fig. 14.3 ):
  1. Group A: normal height.
  2. Group B: less than 50% height loss.
  3. Group B/C: around 50% height loss.
  4. Group C: greater than 50% height loss.
5. Stulberg’s classification: applied at skeletal maturity to prognosticate long-term outcome ⁸ :
  1. I: normal hip.
  2. II: spherical head with enlargement, short neck, or steep acetabulum.
  3. III: nonspherical head, aspherically congruent joint.
    
    Fig. 14.2 Schematic representation of femoral head involvement in the Catterall classification. (Source: Articular Osteochondroses. In: Bohndorf K, Anderson M, Davies E, et al., eds. Imaging of Bones and Joints: A Concise, Multimodality Approach. Stuttgart, Germany: Thieme; 2016)
    
    Fig. 14.3 (a-c) Schematic representation showing the lateral pillar involvement during the fragmentation phase. (Source: Herregods N, Vanhoenacker FM, Jaremko JL, et al. Update on Pediatric Hip Imaging. Seminars in Musculoskeletal Radiology 2017;21(05):561-581)
  4. IV: flat head, aspherically congruent joint.
  5. V: flat head with incongruent joint.
  6. 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
6. 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
  1. In patients requiring treatment, outcomes may be better if initiated prior to fragmentation.
IV. Conway’s classification using bone scintigraphy at diagnosis and again 4 to 5 months later: precedes radiographic changes by 3 months ¹³ , ²¹ :
1. Type A: early and rapid revascularization.
2. Type B:
  1. Centrally located activity or absence of activity in the epiphysis after 5 months.
  2. Higher risk of a poor prognosis.
3. Type C: regression from a type A to a type B, very rare.
V. Magnetic resonance imaging (MRI): can provide a good anatomic picture ⁵ , ¹³ :
1. Flat or round femoral head.
2. Degree of extrusion of the femoral head.
3. Extent of necrosis.
4. Not accurate enough to describe stages of healing.
5. When progressive subluxation of the femoral head is suspected, MRI can be used instead of arthrography.
6. 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 :
1. Likely will show hip effusion.
2. Nonspecific.

Prognostic Factors

I. Age at onset of symptoms: strong prognostic factor with best prognosis in children younger than 5 years. ²² , ²³
II. Gender: conflicting results on whether outcomes are worse in girls. ¹⁶ , ²² – ²⁴
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 :
1. Diffuse metaphyseal reaction.
2. Calcification lateral to the epiphysis: questionable.
3. Gage’s sign: triangular lucent are on the lateral epiphysis.
4. Horizontal capital femoral epiphysis: questionable.
5. Epiphyseal extrusion.
IX. Femoral epiphyseal extrusion: most important ²² :
1. Loss of containment.
2. Lateral subluxation.
3. Predisposes to femoral head deformation.
4. When more than 20% of the width of the femoral head extrudes, there is high chance of the femoral head becoming deformed.
5. More pronounced in older children and with more epiphyseal involvement.
6. Only modifiable factor.
X. Long-term factors associated with poor outcomes in adulthood/development of osteoarthritis ⁸ , ²² :
1. Femoral head asphericity.
2. Steepness of the acetabular roof.