DETERIORATION OF CORTICAL BONE MICROARCHITECTURE IN RENAL OSTEODYSTROPHY – UNDER-REPRESENTED IN THE ‘TURNOVER MINERALISATION VOLUME’ (TMV) CLASSIFICATION?

AK SHARMA1,2, ND TOUSSAINT1,2, GJ ELDER3,4, SG HOLT1,2, P ROBERTSON1,2, PR EBELING5, P BALDOCK4, CS RAJAPAKSE6, R MASTERSON1,2   

1The Royal Melbourne Hospital, Parkville, Australia; 2Department of Medicine (RMH), University of Melbourne, Parkville, Australia; 3Westmead Hospital, Westmead, Australia; 4Garvan Institute of Medical Research, Australia; 5Monash University, Clayton, Australia; 6University of Pennsylvania, PA, USA

Aim: To assess trabecular and cortical bone microarchitecture in patients with chronic kidney disease (CKD) by classical histomorphometry and microcomputed tomography (mCT) of iliac crest biopsies.

Background: Cortical bone contributes significantly to mechanical strength of bone and its deterioration is associated with non-vertebral fractures. Recent imaging and histomorphometric studies demonstrate prevalence of thin cortices and increased cortical porosity in CKD which may have diagnostic and therapeutic implications. Changes in bone microarchitecture as measured by TMV classification do not completely reflect deterioration in cortical parameters.

Methods: Iliac crest bone biopsies were performed in 14 patients undergoing kidney transplantation (n=12) and parathyroidectomy (n=2). Trabecular structural parameters were analyzed by histomorphometry and 3D mCT and included trabecular bone volume, thickness, number and separation. Cortical thickness (CtTh) and porosity (CtPo) were measured by 3D mCT. Bone mineral density (BMD) was measured by peripheral quantitative CT (radius) and dual energy x-ray absorptiometry. Associations were determined by analysis with Spearman’s rank correlation coefficients.

Results: Trabecular parameters from bone biopsy were within normally accepted ranges in most patients. In contrast, all patients showed decreased CtTh and significantly increased CtPo at the iliac crest. CtPo was unrelated to turnover status but demonstrated positive relationship with PTH levels (r=0.62; p=0.021) and was inversely related to trabecular thickness (r=-0.60; p=0.024) at the iliac crest and cortical area (r=-0.59; p=0.045) at the radius. CtTh was also associated with lumbar spine (r=-0.72; p=0.013) and femoral neck BMD (r=-0.55; p=0.07)

Conclusions: Marked deterioration of cortical microarchitecture in the setting of relatively normal trabecular parameters in our cohort reinforces the importance of comprehensive cortical bone evaluation in CKD.

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