ESPE Abstracts

Background: Hypophosphatemic rickets (HR) are rare, inheritable disorders caused by excessive renal phosphate wasting. Despite a generalized mineralization defect, patients with HR are reported with a lower risk of fracture.

Objective and hypotheses: The aim of this study was to evaluate the effect of bone -geometry, -microarchitecture and volumetric BMD (vBMD) on the estimated bone strength in adult patients with HR using high-resolution peripheral quantitative computed tomography (HR-pQCT). As evaluations of BMD in children with HR may be confounded by differences in bone size and bone maturation challenging comparisons with either age- or height matched normal children, only adults with HR were studied.

Method: A total of 29 patients with HR (21 women and eight men, median age 46, range 19–79 years), of which 26 had genetically proven X-linked HR, were included. Patients with HR were age and gender matched with 29 healthy controls.

Results: The patients with HR had significantly higher total bone cross-sectional areas (radius 36%, tibia 20%; both P<0.001) with significantly higher trabecular bone areas (radius 49%, tibia 14%; both P<0.001) compared with controls. In addition, the patients with HR had lower total vBMD (radius −20%, tibia −14%; both P<0.01), cortical vBMD (radius −5%, P<0.001), trabecular number (radius −13%, tibia −14%; both P<0.01) and cortical thickness (radius −19%; P<0.01) compared with controls. The patients with HR had greater trabecular spacing (radius 18%, tibia 23%; P<0.01) and a more inhomogeneous trabecular network (radius 29%, tibia 40%; both P<0.01) compared with controls. Estimated bone strength at both sites was similar between the groups.

Conclusion: In conclusion, in patients with HR, the negative impact of lower vBMD and trabecular number on estimated bone strength seemed compensated by an increase in bone cross-sectional area resulting in HR patients and controls having similar estimates of bone strength.