Unexplained Fractures And Bone Density

Bone Density Measurements by Computed Tomography in Osteogenesis Imperfecta Type I

M. E. Miller1 and T. N. Hangartner2

1Department of Pediatrics and 2BioMedical Imaging Laboratory, Wright State University School of Medicine, Dayton, Ohio, USA

Abstract

The objectives of this study were

(1) todetermine whether there are differences in bone density in children versus adults with osteogenesis imperfecta
type I (OI-type I) using computed tomography (CT) bone density measurements,

(2) to determine whether there are differences in bone density between normal infants and infants with OI-type I using CT bone density measurements and

(3) to determine whether CT bone density measurements could be helpful in investigating the infant with unexplained fractures. CT bone density measurements determine both the cortical bone density (CBD) and the trabecular bone density (TBD).

CT bone density was determined using the OsteoQuant in 14 individuals with OI-type I who ranged in ages from 8
months to 45 years. The control groups consisted of over 1000 normal individuals, mostly adults, and included 7
normal infants who ranged in age from 10 months to 27 months. One of the individuals with OI-type I was a 4-
month-old infant with multiple, unexplained fractures who had no other features of OI-type I and whose parents were accused of child abuse. Infants and children with OI-type I had low CBD and low TBD compared with normal controls, whereas adults with OI-type I had low TBD and high CBD when compared with controls.
The one infant with multiple unexplained fractures and no other features of OI-type I had a bone density profile
suggesting OI-type I with a low TBD and low CBD. Subsequent collagen analysis showed biochemical evidence of OI-type I. Individuals with OI-type I have abnormal CT bone density profiles that evolve over time from a low CBD and low TBD during infancy and childhood to a high CBD and low TBD during adulthood. This may explain the decreased frequency of fractures in individuals with OI-type I in adulthood compared with childhood. Individuals with OI-type I can present with only multiple unexplained fractures and have no other clinical features to strongly suggest the diagnosis.

CT bone density measurements can be helpful in these atypical cases of OI-type I and should be considered in the investigation of the infant with unexplained fractures to help distinguish intrinsic bone disease from child abuse.

Osteogenesis imperfecta (OI) is a group of diseases characterized by bone fragility and fractures with minimal trauma. The most common form of OI is OI-type I, which has a frequency of about 1 in 15 000– 20 000. The clinical features of OI-type I also include short stature, blue sclerae, dentinogenesis imperfecta, hearing loss, wormian bones, and a positive family history – although some of these features may not be present [1]. OI-type I is most commonly caused by the underproduction of a qualitatively normal type 1 collagen. Less often it is caused by the production of a qualitatively abnormal type 1 collagen [2]. In either situation the osteoid that is formed is unable to maintain normal mineralization, and this is the basis of the increased bone weakness and fracture susceptibility. Studies measuring bone density in individuals with OI-type I using the techniques of single- and dual-energy

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