Adaptation of diaphyseal structure with aging and increased mechanical usage in the adult rat: A histomorphometrical and biomechanical study

Abstract

The experimental increase in mechanical usage or overloading of the left hindlimb was produced by immobilization of the contralateral hindlimb. The right hindlimb was placed in a flexed position against the body and was immobilized using an elastic bandage. Some control animals were sacrificed initially at time zero and increased mechanical usage and age-matched control animals were sacrificed after 2, 10, 18, and 26 weeks of treatment. All animals received double bone fluorochrome labeling prior to sacrifice. Cortical bone histomorphometry and cross-sectional moments of inertia were determined. Marrow cavity enlargement and total cross-sectional area expansion represented the age-related cortical bone changes. Increased mechanical usage enhanced periosteal bone modeling in the formation mode and dampened endocortical bone remodeling and bone modeling in the resorption mode (resorption drift) to create a slight positive bone balance. These observations are in general agreement with Frost's postulate for mechanical effects on bone modeling and remodeling (Frost, H.M. 1987b. Bone "mass" and the "mechanostat." A proposal. Anat. Rec. 219: 1-9). The maximum moment of inertia did not change significantly in either control or overloaded tibial shafts. The minimum and polar moment of inertias in overloaded bones increases over those of controls at 18 and 26 weeks of the experiment.

Activation of bone remodeling after fatigue: Differential response to linear microcracks and diffuse damage

“…For example the coefficient of variation for cortical bone area in rodent long bones is in the range of 10-15% (42, 64). As area weighted moments of inertia, these small differences in bone geometry will lead to different structural stiffnesses among bones such that stresses applied to the ulnae (and resulting local strains) will differ among animals for the same applied load magnitude.…”

Effect of vibration on osteoblastic and osteoclastic activities: Analysis of bone metabolism using goldfish scale as a model for bone

“…In addition, the effect of mechanical strain on bone-resorbing activity and mRNA expression of osteoclast marker enzymes (tartrate-resistant acid phosphatase, TRAP; cathepsin K) was examined using isolated osteoclasts (Kurata et al, 2001). In an isolated osteoclast culture, the bone-resorbing activity was up-regulated (Kurata et al, 2001), although it is known that bone mass increases by mechanical strain (Jee et al, 1991;Turner et al, 1991;Mosley et al, 1997;Srinivasan et al, 2003). Therefore, a suitable in vitro model system will be necessary to analyze osteoclastic function under unloading or loading conditions.…”

Human Masticatory Muscle Volume and Zygomatico-mandibular Form in Adults with Mandibular Prognathism

“…Force exerted by a muscle is proportional to the product of the physiological cross-sectional area and fiber length and thus to muscle volume (Van Eijden et al, 1997). The present findings may be explained by previous animal experiments demonstrating that bone mass increases as an effect of mechanical load on long bones (Jee and Li, 1990;Jee et al, 1991) and that the increase in bone mass has a linear relationship with the magnitude of strain (Rubin and Lanyon, 1985). Although inheritance clearly has a strong influence on facial features (Proffit, 1993), skeletal morphology is modified by the mechanical stresses placed on it.…”