Osteogenesis imperfecta (OI) is a rare genetic disease characterised by bone fragility [1]. The radiographic hallmarks of OI are bone deformities, bone fractures, and generalized osteopenia/osteoporosis [2]. Dual-energy X-ray absorptiometry (DXA) is currently the most used and available method to assess bone mineral density (BMD), in both children and adults. However, DXA has notable limitations [3]: (1) it is a two-dimensional technique, yielding only areal BMD (aBMD), which is influenced by bone size and can be confounded by fractures, kyphoscoliosis, and metallic hardware; (2) a standard analysis does not allow to discriminate cortical from trabecular bone; and (3) it does not provide any information on bone microstructure. There is evidence that the increased fracture risk observed in OI is not well predicted by DXA-aBMD alone [4]. In fact, an important contribution of deteriorated bone quality is hypothesized.

High-resolution peripheral quantitative computed tomography (HR-pQCT) is an innovative technique that measures volumetric bone mineral density (vBMD), geometry, and microstructure in vivo at peripheral sites, with low radiation exposure (3-5 µSv per scan) and extremely high resolution (61-82 µm) [5]. HR-pQCT provides separate results for cortical and trabecular bone. The potential of HR-pQCT to complement DXA in the characterisation of bone fragility and in the prediction of fracture risk in post-menopausal and senile osteoporosis is supported by sound evidence [6, 7]. However, only a limited number of studies investigated the use of HR-pQCT in OI [8–11] and the relationship between DXA and HR-pQCT in OI remains undefined. The aim of our study is determining how well DXA-aBMD correlates with HR-pQCT parameters in patients affected by OI.