Fig 1.
Load/Strain Calibration Curve.
This figure demonstrates the linear relationship between applied load and resulting tensile strain at the periosteal mid-diaphysis. For all data points, error bars represent the standard deviation from n = 5 mice.
Fig 2.
Timeline for tibial loading study and waveform profile.
A) The right tibia of each mouse was loaded using the waveform to a set force (8.8N, 10.6N and 12.4N) to elicit a desired periosteal mid-diaphyseal tensile strain level (1700 με, 2050 με and 2400 με) over a 14 day period. B) The loading profile consisted of four haversine waveforms followed by 3 seconds of rest repeated 55 times for a total of 220 cycles of loading per day.
Fig 3.
Location of mechanical tests and micro-computed tomography (μCT) regions of interest.
The diaphysis of each bone was loaded using 4-point bending with the medial surface in tension. The bottom support points (green) were located 9mm apart and the top loading points (blue) were located 3mm apart. The metaphyseal region used for trabecular analyses began just distal to the growth plate in the proximal metaphysis and extended distally by 12% of the overall bone length. The cortical standard site was located 45% the total bone length from the proximal growth plate. Strain gauges used for calibration were in the region spanning the cortical standard site on the anteromedial surface.
Table 1.
Cancellous Architecture in the Proximal Metaphysis.
Fig 4.
Schematic Representations of Standard Site Geometric Profiles.
A) 1700 με group. B) 2050 με group. C) 2400 με group. There was a dose-dependent increase in cortical parameters with robust periosteal and endocortical formation, especially at the higher strain levels. D) 2400 με group with the addition of those animals that experiences a woven bone response due to loading.
Table 2.
Cortical Geometry at the Mid-Diaphysis.
Fig 5.
Schematic representations of mechanical testing curves.
A) Representative structural-level force/displacement curves. B) Estimated tissue-level mechanical curves. At 1700 με, there was no mechanical effect noted. Those limbs loaded to 2050 με experienced significant increases in structural- and tissue-level strength and energy dissipation. The 2400 με group also experienced gains. However, when animals that experienced a woven bone response were removed from the analysis, the gains were more modest (especially at the tissue-level) and most failed to reach significance versus the contralateral control limb given the loss in power. For all data points, error bars represent the standard error of the mean (SEM).
Table 3.
Structural Mechanical Properties From 4-Point Bending of the Mid-Diaphysis.
Table 4.
Estimated Tissue-level Mechanical Properties From 4-Point Bending of the Mid-Diaphysis.