Qualitative bone defect in uremic osteosclerosis.

Osteosclerosis, an increased volume of trabecular bone, is a common but often misinterpreted feature of uremic osteodystrophy. Despite the apparent radiographic density of osteosclerotic bone, pain and fracture may be associated. If accumulated osteoid and woven bone exceed the volume of lamellar bone removed in chronic renal insufficiency, bone density may be reduced despite increased trabecular volume. Concomitant histomorphometric and photon absorption determinations of transileal bone biopsies were done to investigate the relationship between quantity and quality of bone in uremic and non-uremic osteopenic patients. In osteopenic patients with uremia, bone core density had no significant relationship to trabecular bone volume or mineralized bone volume whereas in non-uremic osteopenic patients, these parameters were directly related (r = 0.867 and r = 0.921, respectively, p less than 0.001). The bone core density in the uremic patients was negatively correlated with the total osteoid volume (r = -0.764, p less than 0.05) and positively related to the serum phosphorus concentration (r = 0.739, p less than 0.05). Serum levels of immunoreactive parathyroid hormone (iPTH) and alkaline phosphatase activity were higher in the patients with radiographic osteosclerosis than in the other uremic patients. The lack of correlation between bone volume and density indicates a qualitative defect in uremic bone. It appears that in uremia, elevated iPTH and serum phosphorus levels may augment bone formation, albeit poorly mineralized with woven architecture. While radiographic density paradoxically increases, the amount of normally mineralized bone may be reduced.