Mechanical stress and morphogenetic endochondral ossification of the sternum.

The possible role of mechanical stress in determining the patterns of endochondral ossification in skeletal anlages was explored using stress-analysis computer models of developing human sterna. It has been hypothesized previously that the normal sequence of proliferation, maturation, degeneration, and ossification of cartilage is accelerated in regions of high cyclic octahedral shear stress and inhibited in regions of intermittent compressive-hydrostatic (dilatational) stress. This hypothesis was investigated using two-dimensional, all-cartilage, plane-stress finite-element models of the three basic shapes of human sterna that were identified by Ashley. A mathematical criterion, which combined the opposing influences of the shear and dilatational stresses into a single net stimulus for ossification, was used successfully to simulate the three basic patterns of sternal endochondral ossification that were previously documented. Our findings support the view that mechanical forces may strongly influence skeletal morphogenesis, growth, and development, beginning at a very early stage.