Adaptation of diaphyseal structure to aging and decreased mechanical loading in the adult rat: A densitometric and histomorphometric study

Abstract

Nine-month-old female rats were subjected to right hindlimb immobilization or served as controls for 0, 2, 10, 18, and 26 weeks. They were double-labeled with bone markers prior to sacrifice. Experimental unloading was produced by immobilizing the right limb against the abdomen with an elastic bandage. Single-photon absorptiometry was performed on the intact femurs; static and dynamic histomorphometry were performed on 20-micron thick toluidine blue-stained, undecalcified cross sections of the tibial shafts. Changes in the continuously immobilized tibiae were compared to those in both tibiae of age-matched controls. Unloading shut off nearly all periosteal bone formation and accelerates bone marrow expansion over that which occurs in age-related controls. The effect of unloading appeared to be mediated by recruiting fewer osteoblasts which showed inhibited activity. Furthermore, unloading increased endocortical percentage eroded surface. These histological changes lowered cortical bone mass by inhibiting diaphyseal cross sectional expansion and enlarging the bone marrow cavity. The results support Frost's suggestion that decrease mechanical usage depresses bone modeling-dependent bone gain by decreasing activation of modeling in the formation mode. It also stimulates bone remodeling-dependent bone loss by increasing activation of remodeling in the resorption mode.

Three-point bending and acoustic emission study of adult rat femora after immobilization and free remobilization

“…So, it seems that side-to-side comparison to contralateral bone is more valuable for analyzing any local changes induced by limb immobilization, than comparison to controls. After 3 weeks of hindlimb immobilization (I3) a significant drop of mass in immobilized femora was found in relation to the contralateral bone which was consistent with results of previous experiments on adult rats (Ijiri et al, 1995;Inman et al, 1999;Li and Jee, 1991;Maeda et al, 1993). Taking into account that neither the external size of the femur nor the mineralization of the bone tissue was significantly influenced in our experiment, the decrease of mass may be caused by an increase of marrow cavity and cortical porosity in bone diaphysis as well as by an increase of porosity of cancellous tissue in bone epiphyses.…”

“…Taking into account that neither the external size of the femur nor the mineralization of the bone tissue was significantly influenced in our experiment, the decrease of mass may be caused by an increase of marrow cavity and cortical porosity in bone diaphysis as well as by an increase of porosity of cancellous tissue in bone epiphyses. Such changes are predicted by the theory of structural adaptation of bone to mechanical usage (Frost, 1990), and were proved histologically (Ijiri et al, 1995;Inman et al, 1999;Li and Jee, 1991;Maeda et al, 1993). Variations of crosssectional geometrical properties are mainly responsible for the differences in bending behavior of femur, both from theoretical considerations and as a result of mechanical testing (Martens et al, 1986;Martin, 1991;Strømsøe et al, 1995).…”

Perspectives: A vital biomechanical model of the endochondral ossification mechanism

“…8, middle column). These responses increase resorption and loss of trabecular bone during growth and adult life, and also loss of endocortical bone in adults (Jaworski et al, 1980;Li et al, 1991;Minaire, 1973;Uhthoff and Jaworski, 1978;Weinreb et al, 1989;Wronski and Morey, 1982). Acute partial disuse tends to cause effects between those in total disuse and normal mechanical usage.…”

From Wolff's law to the Utah paradigm: Insights about bone physiology and its clinical applications

“…That should help to explain why strong muscles usually do make strong bones, and chronically weak muscles usually do make weak bones** (Doyle et al, 1970;Frost and Schönau, 2000;Jee, 1999Jee, , 2000Jee and Li, 1990;Jee and Frost, 1992;Li et al, 1990;Li and Jee, 1991;Snow-Harter et al, 1990;Yao et al, 2000). For example, most women have weaker muscles than most men, so they should have less bone strength (and "mass") too.…”