Kinetics of trabecular bone resorption and formation in hypothyroidism: evidence for a positive balance per remodeling cycle.

Using a recently described model for reconstruction of the entire remodeling sequence in trabecular bone after tetracycline double labeling, bone remodeling was investigated in 18 hypothyroid female patients and 11 age- and sex-matched controls. In the hypothyroid group, the final resorption depth was reduced to 42 microns vs 53 microns in the control group (P less than 0.01). The total resorption period was increased to 76 days vs 32 days in the control group (P less than 0.001), and the resorption rate was lowered to 0.8 micron/day vs 2.1 microns/day in the control group (P less than 0.001). The function period for preosteoblast-like cells was 22 days compared to 14 days in normals (P less than 0.05). The total bone formation period was prolonged to 620 days in the hypothyroid group compared to 151 days in the control group (P less than 0.001), and the matrix and mineral appositional rates were lowered to 0.7 and 0.5 micron3/micron2 per day compared to 1.8 (P less than 0.001) and 1.4 (P less than 0.001) micron3/micron2 per day, respectively. The mineralization lag time in the hypothyroid group was 48 days vs 25 days in the control group (P less than 0.001), and at the start of bone formation this difference was even more pronounced (63 and 16 days, respectively, P less than 0.001). The mean completed wall thickness was increased in the hypothyroid group to 59.5 microns compared to 54 micron in the control group (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)