Functional adaptation of bone to increased stress. An experimental study.

In young pigs walking normally, we recorded the principal compressive strains (epsilon 2) as revealed by strain gauges attached to the shaft of the radius. We found no correlation between the mean principal compressive strain and either age or weight in normal animals over the three-month time span of the experiment. Directly after unilateral removal of the ulnar diaphysis, the principal compressive strain on the radial shaft increased by two to two and one-half times its normal value. The increased level of strain in the radius caused by ulnar ostectomy resulted in a rapid and substantial remodeling response in the radius, but three months after ulnar ostectomy, the area of bone enclosed by the periosteal perimeter of the overstrained radius approached the value for the radius and ulna together in the contralateral limb, as did the cross-sectional area of the bone tissue in the mid-shaft of that radius. Three months after unilateral ostectomy, the principal compressive strain was not significantly different in the left and right radii and approached normal values.