Quantifying the strain history of bone: spatial uniformity and self-similarity of low-magnitude strains

We hypothesize that when a broad spectrum of bone strain is considered, str ain history is similar for different bones in different species. Using a da ta collection protocol with a fine resolution, mid-diaphyseal strains were measured in vivo for both weightbearing and non-weightbearing bones in thre e species: dog, sheep. and turkey, with strain information collected contin uously while the animals performed their natural daily activities. The dail y strain history was quantified by both counting cyclic strain events (to q uantify the distribution of strains of different magnitudes) and by estimat ing the average spectral characteristics of the strain (to quantify the fre quency content of the strain signals). Counting of the daily (12-24 h) stra in events show that large strains ( > 1000 microstrain) occur relatively fe w times a day, while very small strains ( < 10 microstrain) occur thousands of times a day. The lower magnitude strains (< similar to 200 microstrain) are found to be: more uniform around the bone cross-section than the highe r magnitude, peak strains. Strain dynamics are found to be well described b y a power-law relationship and exhibit self-similar characteristics. These data lead to the suggestion that the organization of bone tissue is driven by the continual barrage of activity spanning a wide bur consistent range o f frequency and amplitude, and until the mechanism of bones mechanosensory system is fully understood, all portions of bone's strain history should be considered to possibly play a role in bone adaptation. (C) 2000 Elsevier S cience Ltd. All rights reserved.