MRI reveals selective recovery in bone microarchitecture two years following kidney transplantation.

Abstract

To assess longitudinal changes in the microarchitecture and mechanical competence of trabecular and cortical bone over a two-year period following kidney transplantation using high-resolution MRI. MR images at 1.5 T were acquired at the distal tibia and thoracolumbar spine (n = 60, 31 males, ages 20-60 years) at the time of transplantation and six, 12, and 24 months post kidney transplantation. Patients were matched with healthy participants (n = 59) based on age, sex, and body-mass index at baseline. Whole-bone tibia stiffness was estimated using a finite-element model of uniaxial compression tests. Microarchitectural measures of the distal tibia, as well as spine deformity indices of thoracic and lumbar vertebrae, were computed. DXA-derived BMD of the total hip, femoral neck, spine and radius was measured at all time points in kidney transplant recipients. MRI-derived parameters indicate decreased bone quality in kidney transplant recipients compared to healthy participants at baseline. At six months, recipients had a significant deterioration in trabecular thickness (p < 0.001), cortical porosity (p = 0.006), bone volume fraction (BVF, p = 0.005), and tibia stiffness (p < 0.001). However, there were no differences between baseline and 24 months for trabecular thickness (p = 1), BVF (p = 0.19), and cortical porosity (p = 1). Interval glucocorticoid exposure was negatively associated with changes in tibia stiffness (p < 0.0001), BVF (p = 0.049), and trabecular thickness (p = 0.02). By 24 months, total hip BMD increased (p = 0.04), while lumbar spine BMD decreased (p = 0.009). Two years after kidney transplantation and despite sustained low-dose glucocorticoid therapy, MRI noninvasively detected selective and incomplete recovery in some bone microstructural indices while bone stiffness remained persistently reduced.