Skeletal strain induced by planar orbital shaking

The measurement of bone cell response to mechanical stimuli has typically required surgical intervention or administration of anesthetic to deliver skeletal loading. A new noninvasive method of skeletal loading, planar orbital shaking, has been reported to cause an osteogenic response in the preosteoblasts of mice. The purpose of this research was to compare the surface strains induced by planar orbital shaking with ordinary behavioral activities in rats. This information was used to test the hypothesis that orbital shaking delivers greater surface strains than volitional activities. Orbital shaking results of four rats indicate that this new noninvasive method of loading the skeleton did not produce strain magnitudes or strain rates larger than volitional activities. For each animal, strain magnitudes measured during orbital shaking at speeds ranging from 0 to 220 RPM were lower than wheel running. The strain magnitudes during hindlimb suspension, a model of disuse, were evaluated for the rat femur. Stationary hindlimb suspension of two rats reduced the strain magnitudes measured on the rat femurs below strain magnitudes recorded for volitional activities. Ambulation of the animal during hindlimb suspension resulted in strain magnitudes comparable to wheel running, thus suggesting that soft tissues may exert skeletal forces during non-weightbearing activities.