Changes in adipose bone marrow and bone morphology in X-linked hypophosphatemic rickets

Introduction: X-linked hypophosphatemic (XLH) rickets causes significant bone deformities in the lower limbs resulting from a bone mineralization defect. According to Frost's Mechanostat theory, compensatory modeling of the bones takes place during increased mechanical loads. In addition, mechanical stimuli modulate the differentiation of mesenchymal stem cells; common precursors to bone marrow adipocytes and osteoblasts.Hypothesis: Bone deformities of the lower limbs lead to increased femoral bone mass and decreased fatty infiltration of the bone marrow (FIBM) in children with XLH rickets compared to a control group.Patients and methods: Eleven children (10.3 years [6-17]) with XLH rickets and 22 healthy children (10.2 years [5-15.5]) underwent lower limb Magnetic Resonance Imaging. A calculation of FIBM was performed at the mid-femur, as well as a calculation of the total bone cross-sectional area (CSA), the cortical CSA, the anteroposterior and mediolateral axes of the femur, bone marrow and the thickness of the femoral cortices.Results: Total bone CSA, total cortical CSA and bone marrow CSA were higher in the XLH group than in the control group (p < 0.05). The mid-lateral diameters of the femur and bone marrow were more elongated than those of the control group (p < 0.001). Only the anterior cortex was thinned in the XLH group (p = 0.001), while there was no difference with the control group for the posterior, medial and lateral cortices. The total percentage of FIBM was 72.81% [& PLUSMN; 3.95] and 77.4% [& PLUSMN; 5.52] for the XLH and control groups respectively (p < 0.001).Discussion: The increase in bone mass in the XLH population reflects an adaptation of bone tissue to the bone deformities present in this pathology. The decrease in FIBM indicates a lower risk of osteoporosis in the XLH population and may constitute a new monitoring parameter in this pathology. Level of study: III; Case-control study.& COPY; 2022 Elsevier Masson SAS. All rights reserved.