= TREVOR DISEASE = TARSOEPIPHYSEAL ACLASIS

= uncommon skeletal developmental disorder representing an epiphyseal osteochondroma

Prevalence: 1÷1,000,000

Age: 2–4 years; M÷F = 3÷1

Cause: failure of normal progression of cellular cartilage breakdown (= aclasis); spontaneous occurrence

Path: lobulated mass protruding from epiphysis with a cartilaginous cap

Histo: normal bone + hyaline cartilage with abundant enchondral ossification (= abnormal cellular activity at cartilaginous ossification center)

Types:

1. Localized form = monostotic involvement: usually hindfoot and ankle
2. Classic form (>66%) = more than one area of involvement in a single extremity with characteristic hemimelic distribution: talus, distal femur, distal tibia
3. Generalized / severe form = disease involving the whole lower extremity
   • pelvic involvement: femoral head, symphysis pubis, triradiate cartilage
   • hypertrophy of ipsilateral iliac bone

• antalgic (= pain-avoiding) gait; palpable mass
• varus / valgus deformity; limb length discrepancy
• limited joint mobility and function

Location: lower extremity (tarsus, knee, ankle); rare in upper extremity (humerus, ulna, scapula)

Site: restricted to medial OR lateral side of limb (= hemimelic), ie, medial÷lateral = 2÷1

• Infant & toddler
  • premature appearance of an eccentric, lobulated, overgrown, asymmetric ossification center
  • stippled calcification of anomalous cartilage
• Childhood
  • disorganized epiphyseal calcification accompanied by irregular ossification
  • osteochondroma-like growth from one side of epiphysis
  • premature closure of physis results in limb deformity and limb length discrepancy
  • irregular articular surface combined with angular deformity
  • undertubulation of bone as a consequence of secondary involvement of metaphysis

Cx: premature secondary osteoarthritis

DDx: osteochondroma