Pressure algometry to quantify muscle pain in racehorses with suspected sacroiliac dysfunction

Summary Reasons for performing study: Despite the prevalence of orthopaedic injuries to horses, there is no objective means of quantifying the intensity of musculoskeletal pain. Hypotheses: Mechanical nociceptive thresholds (MNT) can be measured repeatably by pressure algometry in horses and MNTs are correlated with both severity of clinical signs and subjective scores of muscle pain on palpation in horses with suspected sacroiliac dysfunction (SID). Methods: The technique of pressure algometry and its repeatability was tested at 4 anatomical sites on either side of the thoracolumbar and pelvic region in 12 Thoroughbreds in training. In a second series of 15 racing Thoroughbreds, using a different set of landmarks, pain on palpation was assessed by pressure algometry. Horses were grouped based on clinical scores of SID as normal (n = 5), mild (n = 5), moderate (n = 4) and severe (n = 1) suspected SID and scored for muscle pain response by manual palpation. Results: Pressure algometry was shown to be a repeatable measure of MNTs. Horses with suspected SID had significantly lower mean MNT when sites and horses were pooled and showed greater differences in mean algometer measurements between left and right sides, compared to control horses. A significant correlation was found between mean pressure algometry measurements and both suspected SID grade and muscle pain response on palpation. Conclusion and potential relevance: Horses with suspected SID displayed lower MNTs compared to control horses, especially in the pelvic region. This supports a potential role for pressure algometry in providing an objective means of quantifying musculoskeletal pain reflected as a reduced MNT associated with SID and its response to physiotherapy or other treatments.