Comparison of Histomorphometry and Computerized Tomography of the Spine in Quantitating Trabecular Bone in Renal Osteodystrophy

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Abstract
Computerized tomography (CT) has the advantage of allowing the isolation of trabecular bone of the axial skeleton, which is the more sensitive to metabolic changes. By means of single-energy X-ray CT we have devised a method for assessing trabecular bone mass (TBM) at L-4 vertebral body, which has an acceptable reproductibility (CV = 2.76%). Normal values where obtained after studying 29 normal individuals from both sexes and different ages. In order to know if the method is accurate, TBM was assessed in 17 patients (6 with creatinine clearance < 6 ml/min and 11 on chronic hemodialysis), and in all of them the results were compared with the histomorphometry of the iliac crest bone biopsy. TBM assessed by CT correlated with trabecular bone volume (TBV; mineralized bone + osteoid) (r = 0.82; p < 0.001) and this correlation was not improved after adding the volume of marrow fibrosis to TBV. TBM assessed by CT also correlated with mineralized bone volume but at a lower level of significance (r = 0.72 ;p = 0.001), and no correlation was found with relative osteoid volume alone. These findings suggest that final CT value is an integral of mineralized bone and osteoid but with a higher influence of mineralized bone. Osteomalacia and osteitis fibrosa were seen in situations of normal, decreased, or increased TBM assessed by CT, although the 2 patients with severe osteosclerosis suffered osteomalacia. We conclude that the assessment of TBM by CT at the axial skeleton of uremic patients has an acceptable reproducibility and accuracy. Its potential role in the management of renal osteodystrophy by noninvasive means must be stablished with repetitive studies in the same subjects, as is suggested by preliminary reports.