The relationship of functional stress and strain to the processes of bone remodelling. An experimental study on the sheep radius

In both growing and adult animals the more highly strained caudal cortex had a lower ash content and a lower elastic modulus than the less highly strained cranial cortex, and the differences between cortices in modulus and ash appeared to be closely related to the greater degree of osteonal remodelling in the morehighly strained cortex.

Abstract

Changes in bone strain were recorded from the cranial (longitudinally convex) and caudal, (longitudinally concave) surfaces of the radial mid-shaft in a number of sheep. These recordings confirmed that during locomotion the cranial surface of this bone was subjected to longitudinal tension and the caudal surface to longitudinal compression. During walking, the peak compression strain on the caudal surface was 1.8 times as great as the peak tension strain on the cranial surface. In both growing and adult animals the more highly strained caudal cortex had a lower ash content and a lower elastic modulus than the less highly strained cranial cortex. Values of elastic modulus and ash content were highly correlated both between cortices and between age groups. The differences between cortices in modulus and ash appeared to be closely related to the greater degree of osteonal remodelling in the more highly strained cortex. The ratio of peak walking stress between the caudal and cranial cortices was calculated to be 1.6:1. The stress values suggest that at every stride during walking, the cranial and caudal cortices of the sheep radius are loaded to within the same proportion of their respective yield stress.