Biomechanics and structural adaptations of the rat femur after hindlimb suspension and treadmill running

Abstract

We microscopically and mechanically evaluated the femurs of rats subjected to hindlimb unloading (tail suspension) followed by treadmill training. Female Wistar rats were randomly divided into five groups containing 12-14 rats: control I (118 days old), control II (139 days old), suspended (tail suspension for 28 days), suspended-released (released for 21 days after 28 days of suspension), and suspended-trained (trained for 21 days after 28 days of suspension). We measured bone resistance by bending-compression mechanical tests of the entire proximal half of the femur and three-point bending tests of diaphyseal cortical bone. We determined bone microstructure by tetracycline labeling of trabecular and cortical bone. We found that tail suspension weakened bone (ultimate load = 86.3 ± 13.5 N, tenacity modulus = 0.027 ± 0.011 MPa·m vs ultimate load = 101.5 ± 10.5 N, tenacity modulus = 0.019 ± 0.006 MPa·m in control I animals). The tenacity modulus for suspended and released animals was 0.023 ± 0.010 MPa·m vs 0.046 ± 0.018 MPa·m for trained animals and 0.035 ± 0.010 MPa·m for control animals. These data indicate that normal activity and training resulted in recovered bone resistance, but suspended-released rats presented femoral head flattening and earlier closure of the growth plate. Microscopically, we found that suspension inhibited new bone subperiosteal and endosteal formation. The bone disuse atrophy secondary to hypoactivity in rats can be reversed by an early regime of exercising, which is more advantageous than ordinary cage activities alone.

The osteogenic effects of swimming on bone mass, strength, and microarchitecture in rats with unloading-induced bone loss

“…In this study, hypoactivity secondary to three weeks of tail suspension effectively impaired bone quality, as shown by reduced bone mass, mechanical weakness, and deterioration of trabecular microarchitecture in suspended rats, when compared to the weight‐matched controls. These findings are in agreement with previous reports in literature, which state that hypoactivity due to hindlimb suspension quickly leads to osteopenia (Falcai et al, ; Shimano and Volpon, ). Our histological and BMD data showed severe trabecular bone loss caused by a relatively short duration of suspension.…”

Skeletal Dysplasias Associated with Mild Myopathy—A Clinical and Molecular Review

“…This is known as the Hueter-Volkman law (Figure 1(b)), which was further defined by Frost in the twentieth century and is often used by clinicians in surgical correction of certain limb deformities [4, 17]. Lack of mechanical loading also results in decreased bone formation, as shown by weightlessness and suspension experiments (Figure 1(a)) [19–21]. …”

Altered Cellular Kinetics in Growth Plate according to Alterations in Weight Bearing

“…However, these studies were performed in different experimental environment (spaceflight) and were conducted in short unloading and reloading periods, so it is not appropriate to compare to our study. Some studies19,20 experimented the simulated weightlessness using the method performed in our study. They reported that the skeleton of growing rats is capable of a rapid recovery from the adverse effects of simulated weightlessness.…”