= severe short-limbed dwarfism

• metaphyseal flaring (Erlenmeyer flask deformity) extending into diaphysis

1. Schmid type (most common)
   autosomal dominant
   • waddling gate
   
   Distribution: more marked in lower limbs; mild involvement of hands + wrists
   • shortened bowed long bones
   • widened epiphyseal growth plates
   • irregular widened cupped metaphyses
   • coxa vara
   • genu varum
   
   DDx: vitamin D–refractory rickets
2. McKusick type
   autosomal recessive (eg, in Amish)
   • sparse brittle hair, deficient pigmentation
   • normal intelligence
   • shortening of long bones with normal width
   • cupped + widened metaphyses with lucent defects
   • short middle phalanges + narrow distal phalanges becoming triangular and bullet-shaped (more frequent in hands than feet)
   • widened costochondral junctions + cystic lucencies
3. Jansen type (less common)
   sporadic occurrence with wide spectrum
   • intelligence normal / retarded
   • serum calcium levels often elevated
   
   Distribution: symmetrical involvement of all long + short tubular bones
   • widened epiphyseal plates
   • expanded irregular + fragmented metaphyses (unossified cartilage extending into diaphyses)
   
   DDx: rickets
4. Pyle disease = Metaphyseal dysplasia
   • often tall
   • often asymptomatic
   
   Distribution: major long bones, tubular bones of hands, medial end of clavicle, sternal end of ribs, innominate bone
   • splaying of proximal + distal ends of long bones with thinned cortex
   • relative constriction of central portion of shafts
   • craniofacial hyperostosis
   • genu valgum