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Finite element model

The biomechanic forces at work within the bovine claw, important factors in the development of lameness in the cow, are impossible to measure directly. We developed computer models that simulated these forces and their effects in the normal claw form and in three diseased claw forms, a flat claw, a contracted claw and a laminitis-type claw.

Measurements of important mechanical characteristics including elasticity modulus values were used to construct the model. Elasticity modulus values in the dorsal region of the claw were higher than in the bulbar region and the sole. This could point to a key biomechanic role that the claw has to play in motion. As it lands on its more elastic palmar/plantar region, the claw assumes a shock absorbing function. As the claw rolls onto the toe and pushes off, the stiffer lateral and dorsal wall allows for a more efficient force transfer.

The correlation of the modulus of elasticity to dry matter levels was proven in the physiological claw, but could not be shown in the material of the pathological claw forms. These results suggest that the obvious deterioration in the horn quality of claws affected by chronic laminitis (grooves, loss of shine, deformation, and discolouration) also led to the significant reduction of the modulus of elasticity, with the moisture content having little effect.

The computer models of the claw were based on so-called finite elements, a technique used often in engineering and architecture. These models were used to evaluate the way normal and pathological forms of bovine feet are loaded when standing on different flooring systems. The finite element model of the normal bovine claw under a load of 756 N (a value representing a normal cow's weight on one foot) showed only minimal deformation, most of which took place at the inner wall. Highest stresses were evident in the proximal inner wall, the outer edge of the weight-bearing surface and under the heels.

The claw-floor contact image showed a pressure distribution resembling the distal rim of the claw wall. On a hard surface, the maximum stresses were three times higher than those on the soft surface. Analyses of the laminitic claw model showed altered stress and strain distributions compared to the sound claw model, with higher burdens on the dorsal margin, the solear surface and the inner wall. The flat dorsal wall angle of the flat claw shifted the major part of the loading to the back part of the claw capsule in the finite element model, leaving the dorsal aspect of the claw showing less stress and strain. The finite element model of the contracted claw indicated mechanical changes especially in the distal outer wall, where the turned-in (contracted) claw wall compresses the underlying soft and hard tissue structures. High stresses were predominately seen in the areas where most horn and claw defects are found in clinical research.

While previous simulations could only calculate stress and strain in the horn capsule, the new full foot model included bone and connective tissue. Deformation seen in the model calculation was seen primarily in the softer tissues of the foot. High levels of strain in the region distal to the tuberculum flexorum correspond to the typical location of sole ulcers in diseased claws.

The possibility of being able to visualise deformation and material stress in the bovine claw on hard and soft surfaces and of using physiological and pathological claw forms, has opened up new perspectives in the study of claw biomechanics. Testing and virtual validation of claw trimming techniques as well as the testing of precisely-defined flooring designs such as slatted or grooved flooring with or without rubber mats could be attempted with this model in the future.

Reported by

Equine Clinic, Orthopedics in Ungulates
Veterinaerplatz 1
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