The daily habitual in vivo strain history of a non-weight-bearing bone

Daily mechanical loading strongly influences the architecture and composition of bone tissue. Throughout the day, the amplitudes, rates, frequencies, and the dispersion over time of these loads vary. Nevertheless, most experimental and descriptive studies on the aforementioned relationship consider only cyclic loading and, in addition, focus on weight-bearing bones. A more complete assessment of the daily loading of bone might lead to a better understanding of the natural everyday stimulus for bone maintenance or adaptive responses. In the present study, we measured the daily habitual strain history of the non-weight-bearing mandible bone in the rabbit. Long-term continuous strain recordings were made using an implantable telemetry device able to read out bone-bonded strain gauges. The lateral surface of the rabbit mandibular corpus was chosen as the bone surface of interest. During the recordings, which lasted up to 33 h, the rabbits (N = 7) were able to move unrestrictedly in their cages, performing their habitual behaviours. Analysis of the recordings revealed that the measured bone surface was subjected to 2.9 (± 1.4) × 103 strain events per hour of which 1.8 (± 1.0) × 103 had amplitudes ≤ 10 microstrains (μɛ). Larger strain amplitudes occurred less often and principal strains fell within the range of −517 (± 118) μɛ to 298 (± 81) μɛ. Strain rates never exceeded 10,000 μɛ/s and only 8.9% (± 7.2%) of the habitual strain rates were higher than 1000 μɛ/s. Strain frequency spectra displayed clear peaks at 4–5 and 9 Hz. The wirelessly recorded daily strain history of the rabbit mandible featured peak strain amplitudes resembling those of other mammalian mandibles, but much smaller than those found in many long-bone strain measurements.