Exploring the use of a standing pressure plate for limb pain detection in high-intensity trained Thoroughbred racehorses

Abstract

Background: In Thoroughbred racing loss of training days due to musculoskeletal injuries (MSI) is a significant threat to the industry. In humans, it is reported that postural sway, as measured from the Centre of Pressure (CoP) displacement, is altered by MSI even before gait adaptations are apparent; the use of pressure plates for that purpose has not been evaluated in horses yet. Aim of the study: To measure the effect of a period of high-intensity workload on the CoP displacement and the static pressure distribution under the fore hooves of Thoroughbred racehorses. Methods: CoP data were captured using a 0.5m Footscan pressure plate over an 8-week period from 15 Thoroughbred racehorses. The horses were from one single training stable where they were trained with a high workload. The horses stood with both forelimbs on the pressure plate. Data were collected at 15 Hz for three sequential one minute recordings per week. The CoP data were filtered using a discrete wavelet transformation with a cut-off frequency of 3.75 Hz and velocity, amplitude and frequency of the CoP displacement were calculated. Pressure scans were collected and analysed to determine the static pressure distribution. Significance level was set at p<0.05. Results: At week 8 there was a significant increase in the frequency of the CoP displacement in the mediolateral axis compared to week 1 (0.28±0.01 vs. 0.30±0.01 Hz, p<0.05). There was no difference in velocity (1.88 ±0.32 vs. 1.87±0.28 mm/s) or amplitude (27.31± 5.09 vs. 22.60±3.77mm). Percentage of the total pressure was consistently greater under the right than the left limb (59.94±1.44% vs. 40.06± 1.44%, p <0.05). More pressure was located under the cranial half of the hoof than the caudal half of the hoof (61.1±1.34% vs. 38.8±1.34%, P<0.05). For left limbs the pressure was higher under the medial side of the hoof than on the lateral side of the hoof (24.1 ±0.88% vs. 21.6±0.8%, p<0.05). Conclusions: The frequency of the CoP displacement seems the easiest reproducible parameter and it changes during eight weeks of training with a high workload and thus might be an indicator of painful limbs. The unloading of the left limb and the lateral side of the left hoof might be due to the counter clockwise training regimen where these areas sustain the most strain. The pressure plate still needs to be validated for CoP measurements.