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Does suppression of bone turnover impair mechanical properties by allowing microdamage accumulation?

One plausible purpose of bone turnover is to repair bone microdamage. We hypothesized that suppression of bone turnover impairs bone quality by allowing accumulation of microdamage. We investigated the effect of high-dose etidronate (EHDP) on bone's mechanical properties and microdamage accumulation. Skeletally mature beagles, 1-2 years old at the beginning of the study, were treated with daily injections of vehicle or EHDP at 0.5 mg/kg per day or 5.0 mg/kg per day for 1 year. X-rays were taken at baseline and monthly from 7 to 12 months. Bones were taken upon sacrifice and biomechanical tests, histomorphometry, and microdamage analyses were performed. Fractures of ribs and/or thoracic spinous processes were found in 10 of 11 dogs treated with the higher dose EHDP. Only one fracture of a thoracic spinous process was found in dogs treated with the lower dose EHDP, and no fractures were found in the vehicle controls. Biomechanical tests showed reduced mechanical strength in ribs and lumbar vertebrae, but not in the femoral diaphysis or thoracic spinous process in the higher dose EHDP group. Histomorphometric measurements showed a significant reduction of cancellous bone turnover in both EHDP-treated groups compared with controls. In dogs treated with the higher dose EHDP, activation frequency was reduced to zero in both cortical and cancellous bone. Osteoid volume increased significantly, especially in trabecular bone, resulting in reduced mineralized bone volume in the higher dose EHDP group. Microcrack numerical density (Cr.Dn) increased significantly only in the lumbar vertebral body in the higher dose EHDP group, but not in the rib or thoracic spinous process where fractures occurred. These findings show that suppression of bone turnover using high doses of EHDP is associated with fractures of the ribs and spinous processes in dogs. This is most likely the result of excessive amounts of unmineralized bone produced by the inhibition of mineralization at these high doses, rather than by the accumulation of microdamage.

Animals↗

Annual injection of vitamin D and fractures of aged bones.

In order to investigate the effect of a supplementation of vitamin D in the prophylaxis of fractures of the bones of aged people, an annual intramuscular injection of ergocalciferol (150,000-300,000 IU) was given to two series of aged subjects: first to 199 (45 male) of 479 subjects (110 male) aged more than 85 years who were living in their own home, and second to 142 (29 male) of 320 (58 male) subjects aged 75-84 and living in a home for aged people. This prospective series was divided into treatment groups according to month of birth. These injections were given annually from September to December in the years 1985-1989, two to five times to each participant. The fracture rates, laboratory values, vitamin D levels, possible side effects, and mortality were followed until October 1990. A total of 56 fractures occurred in the 341 vitamin D recipients (16.4%) and 100 in 458 controls (21.8%) (P = 0.034). The fracture rate was about the same in both outpatient and municipal home series. Fractures of the upper limb were fewer in the vitamin D recipients, 10/341 = 2.9% (P = 0.025), than in the controls, 28/458 = 6.1%, during the follow-up. A similar result was obtained in fractures of ribs, 3/341 = 0.9% and 12/458 = 2.6%, respectively. Fractures of the lower limbs occurred almost as frequently, 31/341 = 9.1%, among the vitamin D recipients as among the controls, 49/458 = 10.7%. The fracture rate was higher in females (22.2%) than in males (9.5%). The fractures were fewer in the vitamin D recipients only in females.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗