In vitro transmission and attenuation of impact vibrations in the distal forelimb

An in vitro model was developed and validated in vivo to quantify the attenuation of impact vibrations, transmitted through the lower equine forelimb and to assess the effects of horseshoeing on this attenuation. The transsected forelimbs of 13 horses were equipped with custom-made hollow bone screws in the 4 distal bones, on each of which a tri-axial accelerometer could be mounted. The limbs were then preloaded while the impact was simulated by dropping a weight on the steel plate on which the hoof was resting. At the hoof wall, the distal, middle and proximal phalanx and at the metacarpal bone, the shock waves resulting from this impact were quantified. To assess the damping effects of shoeing, measurements were performed with unshod hooves, hooves shod with a normal flat shoe and hooves shod with an equisoft pad and a silicone packing between hoof and pad. The in vitro model was validated by performing in vivo measurements using one horse, and subjecting the limb of this horse to the same in vitro measurements after death. Approximately 67% of the damping of impact vibrations took place at the interface between the hoof wall and the distal phalanx. The attenuation of impact vibrations at the distal and proximal interphalangeal joints was considerably less (both 6%), while at the metacarpophalangeal joint 9% of the amplitude of that at the hoof wall was absorbed, leaving approximately 13% of the initial amplitude at the hoof wall detectable at the metacarpus. Compared to unshod hooves the amplitude at the hoof wall is 15% higher in shod hooves. No differences could be observed between shoe types. At the level of the first phalanx and metacarpus the difference between shod and unshod vanished; it was therefore concluded that, although shoeing might influence the amplitude of impact vibrations at the hoof wall, the effect of shoeing on the amplitude at the level of the metacarpophalangeal joint is minimal.