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Introduction
  • A form of dwarfism characterized by irregular, delayed ossification at multiple epiphyses
    • spectrum of disorders with a spectrum of phenotypes
  • Epidemiology
    • prevalence approximately 1:10000
    • presents between age 5-14 years of age
      • location
        • caused by failure of formation of secondary ossification center (epiphysis).
  • Pathophysiology
    • delay of epiphyseal endochondral ossification
    • lack of osseous support yields secondary articular cartilage deformity
    • most commonly affects proximal femur and proximal humerus
  • Genetics
    •  autosomal dominant is most common
      • mutation in COMP  (cartilage oligomeric matrix protein) gene on chromosome 19 (most common and most severe form)
      • mutations type IX collagen
        •  COL9A1, COL9A2, COL9A3
        • causing type II collagen dysfunction because of type IX collagen acts as a link protein for type II collagen
          • necessary for healthy articular cartilage
      • Mutation in Matrillin 3
    • may also be autosomal recessive
      • mutation in SLC26A2 (diastrophic dysplasia sulfate transporter gene)
      • presents with at least one finding at birth
        • clubfoot, cleft palate, clinodactyly
    • up to half of patients with clinical diagnosis of MED do not have the typical genetic mutations
Presentation
  • Symptoms
    • short-limbed, disproportionate dwarfism
    • joint pain
    • waddling gait
  • Physical exam
    • joint deformities from joint incongruity
      • hips are most common joint involved
      • valgus knee deformity common
      • early OA
    • joint contractures
    • short, stubby fingers and toes
    • normal neurologic exam
    • normal intelligence
    • spine is normal
    • normal facies
Imaging
  • Radiographs  
    • demonstrate irregular, delayed ossification at multiple epiphyses
    • may also demonstrate multiple osteochondritis dissecans lesions
    • hip 
      • may show bilateral proximal femoral epiphyseal defects   
        •  distinguished from Leg-Calve-Perthes disease by its symmetric and bilateral presentation, early acetabular changes, and lack of metaphyseal cysts
        • when bilateral Leg-Calve-Perthes is suspected, perform skeletal survey of other joints to rule out MED
      • concurrent avascular necrosis of femoral head 
      • acetabular dysplasia 
    • knee
      • valgus knee
      • flattened femoral condyles
      • double layer patella  
    • hand
      • may show short, stunted metacarpals
      • hyperextensible fingers
    • foot
      • short metatarsals

Differential Diagnosis
  • Spondyloepiphyseal dysplasia
    • distinct in that it also involves the spine
    • typically with a sharp curve
    • atlantoaxial instability
    • cervical myelopathy
    • mutation in type II collagen
Treatment
  • Nonoperative
    • NSAIDS and physical therapy
      • indications
        • early OA
    • childhood hip deformities such as acetabular dysplasia often resolve by skeletal maturity
      •  
  • Operative
    • realigning osteotomy or hemiepiphysiodesis at the knee
      • indications
        • progressive genu varum or valgum
    • total hip arthroplasty
      • indications
        • severe arthritis may present by age 30
 

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Questions (2)

(OBQ08.118) A 9-year-old boy presents for evaluation of shortened stature. He denies back or extremity pain. Physical exam is notable for a valgus left knee and a waddling gait. Radiographs of the pelvis, knees, and left hand are provided in figures A-C. Genetic testing reveals a mutation of the cartilage oligomeric matrix protein(COMP). What is the most likely diagnosis? Review Topic

QID: 504
FIGURES:
1

Multiple epiphyseal dysplasia

84%

(1371/1629)

2

Achondroplasia

2%

(39/1629)

3

Diastrophic dysplasia

7%

(113/1629)

4

Perthes disease

1%

(13/1629)

5

Metaphyseal chondrodysplasia

5%

(87/1629)

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