A method for determination of equine hoof strain patterns using photoelasticity: an in vitro study

During impact, equine hooves undergo viscoelastic deformations which may re sult in potentially harmful strains. Previous hoof strain studies using str ain guages have been inconclusive due to arbitrary guage placement. Photoel astic stress analysis (PSA) is a full-field technique which visually displa ys strains over entire loaded surfaces. This in vitro study identifies norm al hoof strain patterns using PSA. Custom-made photoelastic plastic sheets were applied to the hoof surface. T he hooves were axially loaded (225 kg) under level and varus/valgus conditi ons. Strain patterns were video-recorded through a polariscope. Strains wer e concentrated between middle and distal thirds of the hoof wall regardless of the loading conditions. This strain distribution appears to result from the differential expansion of the hoof wall under load. Increasing load re sulted in higher strains and asymmetric loading resulted in an ipsilateral increase in strain magnitudes without altering strain locations. This study shows that PSA is a reliable method with which to evaluate hoof strains in vitro and is sensitive enough to reflect subtle load-related str ain alterations.