Micro-CT in the Assessment of Pediatric Renal osteodystrophy by Bone Histomorphometry

Background and objectives Computed tomography (CT) measurements can distinguish between cortical and trabecular bone density in vivo. High-resolution CTs assess both bone volume and density in the same compartment, thus potentially yielding information regarding bone mineralization as well. The relationship between bone histomorphometric parameters of skeletal mineralization and bone density from microcomputed tomography (mu CT) measurements of bone cores from patients on dialysis has not been assessed. Design, setting, participants, & measurements Bone cores from 68 patients with ESRD (age =13.9 +/- 0.5 years old; 50% men) and 14 controls (age =15.3 +/- 3.8 years old; 50% men) obtained as part of research protocols between 1983 and 2006 were analyzed by bone histomorphometry and mu CT. Results Bone histomorphometric diagnoses in the patients were normal to high bone turnover in 76%, adynamic bone in 13%, and osteomalacia in 11%. Bone formation rate did not correlate with any mu CT determinations. Bone volume measurements were highly correlated between bone histomorphometry and mu CT (bone volume/tissue volume between the two techniques: r=0.70; P<0.001, trabecular thickness and trabecular separation: r=0.71; P<0.001, and r=0.56; P<0.001, respectively). Osteoid accumulation as determined by bone histomorphometry correlated inversely with bone mineral density as assessed by mu CT (osteoid thickness: r=-0.32; P=0.01 and osteoid volume: r=-0.28; P=0.05). By multivariable analysis, the combination of bone mineral density and bone volume (as assessed by mu CT) along with parathyroid hormone and calcium levels accounted for 38% of the variability in osteoid volume (by histomorphometry). Conclusions Measures of bone volume can be accurately assessed with mu CT. Bone mineral density is lower in patients with excessive osteoid accumulation and higher in patients with adynamic, well mineralized bone. Thus, bone mineralization may be accurately assessed by mu CT of bone biopsy cores. Additional studies are warranted to define the value of high-resolution CT in the prediction of bone mineralization in vivo.