Correlation of quantitative ultrasound of bone with biochemical markers of bone resorption in women with osteoporotic fractures.

The purpose of this study was to examine the correlation of parameters of bone quality assessed by quantitative ultrasound (QUS) with biochemical indexes of bone resorption. QUS of the calcaneus and the hand phalanges, and biochemical parameters (urinary excretion of pyridinoline [Pyr] and deoxypyridinoline [D-Pyr]) were measured in a group of 30 well-characterized postmenopausal women with established osteoporosis and fragility fractures. All patients were treatment free. QUS data significantly correlated with both urinary Pyr and D-Pyr (p < 0.001 for speed of sound [SOS], broadband ultrasound attenuation [BUA], and stiffness at the heel; p < 0.001 for amplitude-dependent SOS at the proximal phalanges of the nondominant hand). No significant correlation was observed between spine and femoral bone mineral density and the urinary excretion of Pyr and D-Pyr. Results of this study suggest that QUS of bone evaluates characteristics of bone influenced by the bone resorption rate.

Immobilization-dependent bone collagen breakdown appears to increase with time: evidence for a lack of new bone equilibrium in response to reduced load during prolonged bed rest.

The purpose of this study was to evaluate the effect of prolonged immobilization on bone, in order to investigate how skeletal turnover adapts to bed rest. We examined indices of bone formation and bone resorption in the serum and urine of fifty-four patients (26 males and 28 females) immobilized after an episode of paralytic stroke. The length of immobilization ranged from 30 to 180 days. A significant, time-dependent increase in markers of resorption - urinary pyridinoline (Pyr) and deoxypyridinoline (D-Pyr), serum Type I collagen cross-linked C-telopeptide (ICTP) - was observed in immobilized patients, as compared to free-living healthy subjects. The positive correlation between resorption markers increase and the length of immobilization suggests that the rate of bone resorption did not decrease with time. On the other hand, the levels of markers of bone formation - bone-specific alkaline phosphatase (B-ALP), and the carboxyl-terminal propeptide of Type I procollagen (PICP) - remained within the normal range in all patients, regardless the length of immobilization. Our results would indicate an uncoupling between bone formation and bone resorption during bed rest, and suggest that the bone collagen break-down was not a self-limiting process in immobilized patients, and that a new equilibrium or "steady state" in response to the reduced load was not reached in the skeleton.