Disuse-induced deterioration of bone strength is not stopped after free remobilization in young adult rats.

The effect of unilateral hindlimb immobilization and subsequent free remobilization on mechanical properties of femur was examined in young adult rats. Right hindlimb of 17 weeks old male rats was immobilized for 2 weeks. Rats were sacrificed either directly after immobilization (E0) or after 4 weeks of free remobilization (E4). Mechanical properties in three-point bending as well as dry mass (m(dry)), geometry, apparent density (d(app)), and mineralization of dry bone tissue were measured post mortem in right and left femora of experimental rats (E0, E4) and in right femora of age-matched controls (C0, C4). Differences between right femora of experimental and control animals and between right and left femora of experimental animals were analyzed. After immobilization only d(app) in E0 was significantly lower than in C0. Side-to-side differences in E0 were present only in m(dry) and d(app). Surprisingly, 4 weeks after remobilization the differences between experimental and control femora were more pronounced. Mineralization, d(app), maximum bending moment (M(max)), yield bending moment (M(y)) and stiffness of the right femur were lower in E4 than in age-matched C4. Side-to-side differences in remobilized rats (E4) were still significant for m(dry) and d(app). Additionally, the medullary area was larger, and M(max), M(y), stiffness and work to failure were lower in the right femur than in the left. It is concluded, that the processes of bone deterioration initiated during immobilization do not cease immediately after resumption of normal mechanical loading.

Ultrasound velocity and attenuation in cancellous bone samples from lumbar vertebra and calcaneus.

We report a study of ultrasound velocity and broadband ultrasound attenuation (BUA) in human cancellous bone samples. The influence of density and microarchitecture on ultrasound propagation in cancellous bone was examined. A total of 20 samples from vertebra L1 and 21 from calcanei were studied. The direction of ultrasound propagation was anteroposterior in the vertebra and lateromedial in the calcaneus. The relationships between ultrasonic parameters and density of bone samples, apparent ash density, trabecular bone volume (BV/TV) and trabecular thickness (Tb.Th) were analyzed using a simple linear model and a multiple regression model. Velocity of ultrasound and BUA were positively correlated with density and morphometric parameters, in both vertebra and calcaneus. The best correlation was found between velocity and bone sample density in vertebra (r = 0.961, p < 0.0001) and the worst between velocity and trabecular thickness in calcaneus (r = 0.632, p = 0.002). The best correlation for BUA was with BV/TV in vertebra (r = 0.960, p < 0.0001). Using the stepwise regression procedure, BV/TV only was selected as significant for BUA and apparent ash density with Tb.Th for velocity, in both vertebra and in calcaneus. The possible influence of trabecular configuration on ultrasonic parameters is discussed, emphasizing the different slopes of regression lines obtained for vertebra and calcaneus, sites with different architecture of trabecular bone.