Bone Abstracts

Although X-linked hypophosphatemic rickets (XLH) is characterized by hypophosphatemia leading to a generalized mineralization defect with rickets (and/or osteomalacia), densitometric studies point towards a tendency towards an elevated bone mineral density (BMD). The aim of this cross-sectional in vivo study was to assess bone geometry, volumetric BMD (vBMD), microarchitecture and estimated bone strength using high-resolution peripheral quantitative computed tomography (HR-pQCT) in patients with XLH. After receiving the Regional Ethical Committee approval, 28 patients with genetically proven XLH aged 45.5±16.2 years (21 females, 7 males) were matched with respect to age and gender with 31 healthy subjects aged 46.6±16.4 years. Eleven patients were currently receiving therapy with calcitriol and phosphorus with a median duration of treatment of 29.1 years (12.0 to 43.0 years). Due to the disproportionate short-stature in XLH, HR-pQCT images at the distal radius and tibia were obtained at a region of the bone in a constant proportion to the entire length of the bone, in both, patients and healthy volunteers. In age and weight adjusted models, XLH patients had a significantly enlarged mean total bone cross-sectional areas (radius 33%, tibia 18%; both P<0.001) with significantly higher trabecular bone areas (radius 39%, tibia 18%; both P<0.001). There was a reduction in total vBMD (radius −13%, tibia −12%; both P<0.01), cortical vBMD (radius −5%, P<0.01), trabecular number (radius −14%, tibia −16%; both P<0.01) and cortical thickness (radius −16%; P<0.01), while the trabecular thickness (radius 13%, P=0.05) and trabecular spacing (radius 21%, tibia 23%; P<0.01) were increased. Estimated bone strength was similar between the groups. In conclusion, the negative impact of a reduction in volumetric density and trabecular number on bone strength, was compensated by an overall increase in bone size and thickness of the individual trabeculae, resulting in patients with XLH having similar estimates of bone strength as healthy subjects.