Trabecular bone remodeling and balance in primary hyperparathyroidism

Abstract

The total remodeling sequences in 19 primary hyperparathyroid patients and 16 approximately age-matched and sex-matched controls were reconstructed from histomorphometric analyses of bone specimens obtained after intravital tetracycline double labeling. In the primary hyperparathyroid group the total amount of work performed by resorptive cells was reduced, as indicated by the significantly lower three-dimensional mononuclear and preosteoblast-like cell resorption depths (35.8 μm vs 44.5 μm in normals, P < 0.01 and 45.3 μm vs 56.6 μm in normals, P < 0.01, respectively). The active resorption period (i.e., the function period for osteoclasts and mononuclear cells) was reduced to 19 days compared to 29 days in normals ( P < 0.05), but no difference with respect to bone resorption rates could be demonstrated between the two groups. The median bone formation period (Sigma f) in primary hyperparathyroid patients was not different from the value obtained in normals (172 days vs 134 days, respectively), and the matrix appositional rate (A ma), as well as the mineralization lag time (t m), were also unchanged. The initial mineralization rate (A mi(i)) was not significantly different from the value obtained in normals, but averaged over the total bone formation period, a reduced mineralization rate could be demonstrated (0.32 μm 3 μm 2 per day vs 0.46 μm 3 μm 2 per day in normals, P < 0.01). The measured final three-dimensional thickness of bone formed during Sigma f (mcwT m) was reduced in the primary hyperparathyroid group (51.1 μm vs 55.9 μm in normals, P < 0.02). The balance between resorption and formation was analyzed using measured as well as growth curve-based estimates for mean thickness of completed walls (mcwT m and mcwT c, respectively). Dependent on the values used, a zero to slightly positive balance between resorption and formation was calculated. The birth rate of new remodeling cycles (μ), defined as the frequency by which a given point on the trabecular surface undergoes new remodeling, was increased in the group of primary hyperparathyroid patients (19 × 10 −4 days −1 vs 12 × 10 −4 days −1 in normals, P < 0.05).