Genetically and clinically, heterogeneous group of connective tissue disorders presenting with osteoporosis and fractures

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  90% of cases due to abnormalities in type I collagen

Newer osteogenesis imperfecta (OI) nomenclature further subdivides 5 classic phenotypes

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  Type II (perinatal lethal OI) with most obvious in utero findings

Presence of fractures distinguishes OI from most other skeletal dysplasias

Long bone shortening/angulation secondary to fractures

Callus formation gives bones crumpled appearance

Poor mineralization especially noticeable in skull

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  Skull deformation from normal transducer pressure

  
  
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  Anatomy “seen too well” with no reverberation artifact

Small chest with beaded (fractured) ribs

Hypophosphatasia has generalized demineralization

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  Bones are thin and bowed but true fractures uncommon

Achondrogenesis

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  Unossified spine is key finding, type 1A with rib fractures

1st-trimester endovaginal US in high-risk patients

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  Normal US does not exclude OI in high-risk patients

Measure all long bones/assess for fractures

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  Severe shortening in perinatal lethal form

  
  
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  Pay special attention to femora

  
  
  
  
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    Less severe forms may present with apparently isolated bent femora

  
  

Apply gentle pressure while scanning brain to look for flattening of calvarium

Scan chest in coronal plane to look for beading of ribs

Compare chest to abdominal circumference

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  Small chest → increased risk for pulmonary hypoplasia