Musculoskeletal Imaging

Osteogenesis imperfecta

an inherited disorder of connective tissue in which various structures are affected (skeleton, ligaments, skin, sclerae and denting), expressed either as an abnormal synthesis (quantity) or abnormal structure (quality) of procollagen I. Osteogenesis imperfecta has four major clinical criteria, the presence of two of which are required to make the diagnosis:

  • osteoporosis with abnormal fragility of the skeleton;

  • blue sclera;

  • dentinogenesis imperfecta; and

  • premature otosclerosis.

    Among the other manifestations of osteogenesis imperfecta are ligamentous laxity, easy bruisability, constipation, hyperplastic scars and premature vascular calcifications. Although classically two forms have been recognized (the congenita form, which has a high infant mortality rate, and the tarda form, in which life expectancy is normal), a newer classification system based on a combination of clinical, radiographic and genetic factors has largely replaced these terms (Table 1).

    Osteogenesis imperfecta, Table 1. Classification of osteogenesis imperfecta.

    Type I
    Most common and mildest phenotypic form
    Bone fragility with an increased number of fractures
    Dwarfing or bowing deformities not present
    Type II
    Lethal form
    Severe bone fragility leads to dwarfing and fractures in utero
    Type III
    Rare phenotypic variety
    Fractures generally present at birth
    Severe bone fragility; surviving patients exhibit the most dramatic dwarfing among osteogenesis imperfecta cases
    Type IV
    Most variable bone findings

    The most characteristic radiographic finding of osteogenesis imperfecta is a diffuse decrease in bone density of variable degree involving the axial and appendicular skeleton equally. In the extremities, patients may exhibit one of three radiographic patterns:

  • thin, gracile bones;

  • short, thick limbs; and

  • bones with cystic changes.

    Sometimes the radiographs change from one appearance to another during periods of active bone growth. The fractures are usually transverse and occur most often in the lower extremities; avulsion injuries are also common. Although fracture healing is usually normal, tumoural callus, sometimes mimicking osteosarcoma, and pseudarthrosis may occur. Children may reveal multiple scalloped radiolucent areas with sclerotic margins (popcorn calcifications) in the metaphyses or epiphyses of the long bones.

    Other radiographic features include enlargement of the frontal and mastoid sinuses, overtubulation of tubular bones, wormian bones, platybasia with or without basilar impression, flattening of the vertebral bodies, severe kyphoscoliosis and multiple thoracic deformities (fractured and beaded ribs, pectus carinatum). In the pelvis, a triradiate pelvis, compression fractures, protrusio acetabuli and shepherds crook deformity of the femora may be present.

    Various treatment procedures have greatly improved the outlook in this disease, including the Sofield procedure, multiple osteotomies and intramedullary rodding techniques used since 1959.

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