The influence of equine hoof conformation on the initiation and progression of laminitis.

BACKGROUND: The health and performance of horses are significantly affected by diseases associated with the hoof. Laminitis is a critical hoof disease that causes pain and, potentially, severe hoof and bone pathology. OBJECTIVE: To generate an equine hoof finite element (FE) model to investigate the impact of normal and toe-in hoof conformations on the degeneration (decrease in elastic modulus) of the laminar junction (LJ), as occurs in chronic laminitis. STUDY DESIGN: Computer software modelling. METHODS: A hoof FE model was generated to investigate the biomechanics of hoof laminitis. A 3D model, consisting of nine components, was constructed from computed tomography scans of an equine left forelimb hoof. The model was loaded with 100 cycles of trotting. Two different centres of pressure (COP) paths representing normal and toe-in conformations were assigned to the model. LJ injury was modelled by degenerating the tissue's elastic modulus in the presence of excessive maximum principal stresses. RESULTS: FE models successfully showed findings similar to clinical observations, confirming third phalanx (P3) dorsal rotation, a symmetric distal displacement of the P3 (2 mm at the lateral and medial sides) in the normal model, and an asymmetric distal displacement of the P3 (4 mm at the lateral and 1.5 mm at the medial side) in the toe-in model. The proximal distance between P3 and the ground after LJ degeneration in the current model was significantly different from experimental measurements from healthy hooves (P < 0.01). MAIN LIMITATIONS: The inability to account for variations in population geometry and approximation of boundary conditions and system relations were the limitations of the current study. CONCLUSIONS: The distribution of LJ tissue degeneration was symmetric at the quarters in the normal hoof and in comparison, there was a lateral concentration of degeneration in the toe-in model.

HISTORIAL: La salud y el desempeño atlético de los caballos son afectados por patologías asociadas al casco. La laminitis es una enfermedad critica del casco que causa dolor y, potencialmente, patología severa del casco y ósea. OBJETIVO: Generar un modelo finito del casco equino para investigar el impacto de la conformación normal y del dedo-hacia-adentro sobre la degeneración (reducción del módulo elástico) de la unión laminar (UL), como ocurre en la laminitis crónica. DISEÑO DEL ESTUDIO: Modelado por computadora. MÉTODOS: Un modelo de elemento finito (EF) de casco fue generado para investigar la biomecánica de la laminitis en el casco. Un modelo 3D, que consistía de nueve componentes, fue construido a partir de imágenes de tomografía computarizada de un casco equino izquierdo. El modelo fue cargado con 100 ciclos de trote. Dos vías con centros de presión (VCP) distintos representando la conformación normal y dedo-hacia-adentro fueron asignadas al modelo. La lesión de la UL fue modelada degenerando el modelo elástico del tejido en la presencia de estrés principales excesivos máximos. RESULTADOS: Los modelos EF mostraron exitosamente hallazgos similares a las observaciones clínicas, confirmando que la rotación dorsal de la tercera falange (F3), con un desplazamiento distal simétrico de F3 (2 mm por medial y lateral) en el modelo normal, y un desplazamiento distal asimétrico de F3 (4 mm por lateral y 1.5 mm por medial) en el modelo dedo-hacia-adentro. La distancia proximal entre F3 y el suelo después de la degeneración de la UL en el modelo actual fue significativamente diferente de las mediciones experimentales de casco saludables (P < 0.01). LIMITACIONES DEL ESTUDIO: La inhabilidad de tomar en cuenta las variaciones en la geometría de la población y la aproximación de condiciones marginales, y relaciones de sistemas fueron las limitantes de este estudio. CONCLUSIONES: La distribución de la degeneración del tejido de la UL fue simétrico en los cuartos en el casco normal, hubo una concentración lateral de la degeneración en el modelo dedo-hacia-adentro. PALABRAS CLAVE: laminitis, conformación del casco del caballo, centro de presión, método de elemento finito, modelo hiperelástico.

The influence of equine limb conformation on the biomechanical responses of the hoof: An in vivo and finite element study.

Hoof conformation plays a key role in equine locomotion. Toe-in conformation is an abnormal condition characterized by inward deviation of the limb from its frontal axis. Several studies have documented differences in hoof deformation and hoof kinematics in horses with toe-in and normal hoof conformations. However, the reason behind this has yet to be understood. The present study hypothesizes that a different center of pressure (COP) path underneath the hoof is the cause of different deformation patterns and hoof kinematics in toe-in hooves. In vivo measurements and finite element (FE) analysis were conducted to test the hypothesis. A normal and a toe-in limb were considered for in vivo strain measurements. Strains were measured at three different sites on the hoof wall, and the stride characteristics were investigated using video recording. The magnitude of the minimum principal strain measured at the medial aspect of the toe-in hoof was much lower relative to the normal hoof. Furthermore, the toe-in hoof had a different movement pattern (plaiting) compared to the normal hoof. In the second study, an entire hoof model was simulated from computed tomography (CT) scans of an equine left forelimb. The Neo-Hookean hyperelastic material model was used, and the hoof was under dynamic loading over a complete stride at the trot. Two different COP paths associated with normal and toe-in conformations were assigned to the model. The FE model produced the same in vivo minimum principal strain distributions and successfully showed the different kinematics of the toe-in and normal hooves.

Linear elastic and hyperelastic studies of equine hoof mechanical response at different hydration levels.

Most simulation studies on equine hoof biomechanics employed linear elastic (LE) material models. However, the equine hoof wall's stress-strain relationship is nonlinear and varies with hydration level. Therefore, it is essential to investigate the accuracy of the LE model compared to more advanced material models, such as hyperelastic (HE) or viscoelastic models. The current research investigated performances of LE and three HE models (Mooney-Rivlin, Neo-Hookean, and Marlow) in describing equine hoof's mechanical behavior using finite element (FE) analysis. In the first attempt, a rectangular tissue specimen was simulated using the previously published experimental data. The Marlow HE model predicted the hoof wall stress-strain curve more accurately than the LE, Mooney-Rivlin, and Neo-Hookean models. The LE model accuracy, compared with the experimental results, varied within the reported range of the strain. However, the Marlow HE model perfectly matched the experimental data for a wide range of strains. In the second attempt, the entire hoof, including nine associated tissues, was modeled from computed tomography (CT) scans of an equine forelimb, and analyzed at trotting and standing modes of locomotion. The effect of environmental humidity on the hoof wall material properties was incorporated at four hydration levels; 0%, 53%, 75%, and 100%. The simulation results of the LE and HE models indicated that the minimum principal strain distribution on the hoof wall remained under 2% for various hydration levels and gait conditions. The numerical results of the Marlow HE model demonstrated better agreement with published experimental data compared to the LE, Mooney-Rivlin, and Neo-Hookean models. Higher hydration levels significantly increased the strains - a potential explanation could be the fact that the higher hydration levels decreased stiffness of the hoof wall tissues and ultimately increased strains. Higher ground reaction forces increased the von Mises stress at various points in the hoof wall, especially in the quarter regions and close to the coronet, where cracks and fractures are found more often in the physiological conditions.