The effect of a reverse shoe and polystyrene padding on the biomechanics of the front hoof of the horse

Abstract

The aim of this study was to investigate the effect of reverse shoes, partial dorsal hoof wall removal and polystyrene solar support on the biomechanics of the front hoof of the horse. Laminitis is a systemic syndrome that ultimately affects the sensitive lamellae and papilla of the hoof, causing severe pain, and often leading to disruption of the lamellae-hoof wall interface. Degeneration of the lamellar interdigitation occurs and the distal phalanx (P3) separates from the hoof wall. This can cause P3 to rotate towards the sole and, in more severe cases, P3 separates totally from the hoof wall and sinks downwards. Chronic laminitis usually results in the end of the animal’s athletic career and may lead to humane destruction During an in vitro study, three clinically healthy horses were euthanased and their dismembered forelimbs were used. A reverse shoe was applied and three polystyrene pads with a density of 32 kg/m3, thickness of 60mm and wedges of 66%, 50% and no wedging, respectively, were used in this study. Fuji Prescale Super and Ultra Super Low-Pressure film was used to indicate the pressure distribution of the polystyrene on the solar surface of the hoof. Two load cells were used to measure the load borne by the hoof wall and the solar area, respectively. A constantly increasing force with a maximum of 66% of the bodyweight of the horse was applied to the amputated limb by means of a tensile testing machine. A total of four experiments were done on each limb. The results of this investigation showed that for all three of the polystyrene paddings, approximately 75 - 80% of the total load applied was borne by the solar area. The colour changes on the pressure film showed that most of the load of the 50% and 66% wedged polystyrene was borne by the palmar half of the solar surface, and less pressure by the dorsal half. For no wedging, the pressure distribution over the solar surface was even. The reverse shoe with the 66% and the 50% wedged polystyrene pads was shown to be useful in distributing the pressure to the palmar area of the sole. During an in vivo study, the effect of different densities (32 kg/m3, 24 kg/m3 and 16 kg/m3) and different thicknesses (100mm and 60mm) of polystyrene padding, with a wedge of 50%, on the load distribution of the solar surface and the hoof wall was investigated. Compression of polystyrene over time and the effect thereof on the load distribution was determined. The front hooves of three clinically healthy horses with a mean bodyweight of 551 kg, were trimmed and shod with reverse shoes. Reference data was recorded with only the reverse shoes on the hooves. Further data recording was done for the different polystyrene pads. Data was recorded for 4 seconds with a frequency of 50Hz. Between the treatments, the horses walked for 5 minutes on a concrete surface. This procedure was repeated 5, 10 and 15 minutes after application of the pads. All the results of the solar pads used in the in vivo study showed a hyperbolic tendency in which the initial load was high and then diminished with time. Initially, treatments 5 (32 kg/m3 x 60 mm) and 3 (16 kg/m3 x 60mm) proved to be the better treatments, but after 15 minutes no significant different was found between the treatments. From the observations made during the experimental procedure, the 32 kg/m3 x 60mm (treatment 5) compressed to a more dense and rigid end-product than the 16 kg/m3 x 60mm (treatment 3). The compressed pad of treatment 3 was more elastic and may have contributed positively to reducing the compression of the pads on the blood vessels underneath P3. Observations made during the experimental procedures indicated that polystyrene with a thickness of 100mm, is not recommended. This polystyrene was very uncomfortable for the horse immediately after application. Some polystyrene compressed outside the solar surface and was therefore not adequate for the object of the study. It was concluded that polystyrene pads with densities of 32kg/m3, 24kg/m3 and 16kg/m3 and thicknesses of 100mm and 60mm would prove similar support for the remainder of the period that they were applied follow a variable compression phase of less than 15 minutes. Further research need to be done to investigate the effect of the polystyrene pad on the solar surface for a longer period. Copyright