Pressure algometry for the detection of induced back pain in horses: a preliminary study

REASONS FOR PERFORMING STUDY: Pressure algometry (PA) is a potential modality for objectively measuring mechanical nociceptive thresholds (MNTs) in horses. Its ability to differentiate musculoskeletal pain sites from nonpain sites is unknown and must be assessed prior to its clinical application. OBJECTIVES: To assess the ability of PA to detect induced musculoskeletal pain. METHODS: Twenty clinically normal mature horses (2 groups of 10 horses, over 2 years) were used to measure MNTs before and after implantation and removal of 2 fixation half-pins in the dorsal spinous processes of 2 adjacent vertebrae. To assess hyperalgesia, MNTs near the surgical sites were pooled and compared to surrounding landmarks. MNTs were also compared on 2 consecutive days immediately after surgical implantation. To assess longer-term adaptation or sensitisation, changes from the beginning to the end of the study were evaluated. RESULTS: The precise surgical sites could be recognised due to substantial and localised decreases in the MNTs compared with surrounding landmarks. At most sites distant to the surgical sites, the distribution of the median percentage change in MNTs was centred around 0 (suggesting unbiased repeatability). MNTs compared from the beginning to the end of this study did not demonstrate obvious adaptation or sensitisation. CONCLUSIONS AND POTENTIAL RELEVANCE: PA provides a quantitative and repeatable method for assessing the presence of musculoskeletal pain. Further studies are needed to evaluate PA clinically for assessing musculoskeletal injuries and pain management strategies in horses.