Photoelastic stress analysis of strain patterns in equine hooves after four-point trimming

Abstract

Objective - To evaluate changes in strain patterns in normal equine hooves following 4-point trimming, using photoelastic stress analysis. Sample Population - 15 equine front limbs with normal hoof configuration. Procedure - Limbs were disarticulated at the carpometacarpal joint. Weight-bearing surfaces of each hoof were trimmed level to ensure 100% ground contact. Hoof walls were coated with a custom-made strain-sensitive plastic, and limbs were loaded to a third of body weight. Using a polariscope, strain distribution, magnitudes, and directions were evaluated in level hooves as well as before and after standardized 4-point trimming. Repeated-measures ANOVA was used to compare strain magnitudes and directions before and after trimming. Results - In leveled specimens, strain fields were symmetrically distributed above the heels and at quarter-toe junctions along a line between the middle and distal thirds of the hoof wall. After 4-point trimming, strain epicenters localized above the contact points, whereas strain magnitudes significantly increased by approximately 50%. Decreasing contact area by 50% resulted in an additional significant increase (32%) in strain magnitude. Trimming did not have a significant effect on strain orientations. Conclusion and Clinical Relevance - This study documents that 4-point trimming results in strain concentration above the hoof contact points and that strain magnitude is dependent on contact area.