- Osteogenesis imperfecta (OI) is a common heritable disorder of collagen synthesis that results in weak bones that are easily fractured and often deformed.
- The primary pathology in OI is a disturbance in the synthesis of type I collagen, which is the predominant protein of the extracellular matrix of most tissues.
- Besides bone, type I collagen is also a major constituent of dentin, sclerae, ligaments, blood vessels and skin.
- Several distinct subtypes have been identified. All of them lead to variable degrees of micromelic dwarfism (shortening of the entire limb).
- Depending on severity, the bone fragility may lead to perinatal death or cause severe deformities into adulthood.
- Four distinct types are identified. In general, type I is the mildest form of disease, whereas types IV, III, and II indicate increasing severities of disease.
- Type I, or dominantly inherited form with blue sclerae
- Type II, or perinatal lethal form
- Type III, or progressively deforming form with normal sclerae
- Type IV, or dominantly inherited with normal sclerae.
 Imaging Findings
 Plain film
- Sine qua non of OI is generalized osteoporosis of both the axial and appendicular skeleton.
- Milder forms of OI result in thin, overtubulated bones with thin cortices, and relatively few fractures. The short tubular bones are also affected, though they are less frequently fractured.
- More severe forms of OI, such as in types II and III, feature thickened, shortened long bones with multiple fractures; these forms are often complicated by hyperplastic callus formation.
- Radiographs of the skull may reveal normal skull development in milder forms of disease. With increasing disease severity, the skull demonstrates poor mineralization and multiple wormian, or intrasutural, bones.
- The chest may be small. Multiple rib fractures are often found; these can cause the ribs to become broad and deformed.
- Spinal abnormalities in all subtypes include basilar invagination, platyspondyly, and scoliosis.