Understanding of the diversity of skeletal loading regimes in vertebrate long bones during locomotion has been significantly enhanced by the application of planar strain theory (PST) to in vivo bone strain data. PST is used to model the distribution of longitudinal strains normal to the bone's transverse cross-section and the location of the neutral axis of bending. To our knowledge, the application of this theory to skeletal biomechanics has not been experimentally validated. We evaluated the accuracy of PST using strain measurements from emu tibiotarsi instrumented with four strain gauges and loaded in ex vivo four-point bending. Using measured strains from three-gauge combinations, PST was applied to predict strain values at a fourth gauge's location. Experimentally measured and predicted strain values correlated linearly with a slope near 1.0, suggesting that PST accurately predicts longitudinal strains. Additionally, we assessed the use of PST to extrapolate shear strains to locations on a bone not instrumented with rosette strain gauges. Guineafowl tibiotarsi were instrumented with rosette strain gauges and in vivo longitudinal and shear strains were measured during treadmill running. Individual-specific and sample-mean ratios between measured longitudinal strains from the medial and posterior bone surfaces were used to extrapolate posterior-site shear strain from shear strains measured on the medial surface. Measured and predicted shear strains at the posterior gauge site using either ratio showed trends for a positive correlation between measured and predicted strains, but the correlation did not equal 1.0 and had a non-zero intercept, suggesting that the use of PST should be carefully considered in the context of the goals of the study and the desired precision for the predicted shear strains.
The authors declare no competing or financial interests.
K.A.V., R.P.M. and L.P.L. designed the experiments and test protocols. K.A.V., R.P.M., and M.L. conducted the experimental tests. K.A.V. conducted primary data analysis. K.A.V., L.P.L. and R.P.M. drafted and revised the manuscript.
This work was supported by the National Science Foundation [NSF GRF to K.A.V., DGE-1333468] and The Company of Biologists (JEB travelling fellowship to L.P.L.).
- Received November 9, 2015.
- Accepted July 22, 2016.
- © 2016. Published by The Company of Biologists Ltd