Acoustic Myography: Its Assessment of Ground Reaction Forces as Measured through Forelimb and Hind Limb of the Horse during Mild Exercise

Abstract

Background: Fractures in the limbs of racehorses are common, resulting among other factors, as the result of repeated ground reaction forces on bones and joints, leading to catastrophic failure. Aim: To quantify ground impact transmission through the limb bones of un-shod healthy horses using the non-invasive technique of acoustic myography (AMG). Methods: Four sites were selected for AMG measurements at the walk and trot, hoof wall (site 1) and sites 2 - 4, metacarpal 3, carpals and the radius of the left forelimb of two healthy horses. Measurements were on both rubber and concrete. AMG of the equine hind limb suspensory system was made and analyzed (amplitude and timing) for the proximal suspensory ligament (PSL) and the SDFT/DDFT. Results: AMG signal amplitude at site 1 (1.5 ± 0.2 versus 1.1 ± 1.5) was not found to be significantly different at the trot compared to the walk; however, sites 2, 3 and 4 were all significantly different when compared between the two gaits; site 2 P = 0.008; site 3 P = 0.006; site 4 P = 0.005. AMG signals recorded on the rubber surface had smaller amplitude than the equivalent signal and site on the concrete surface. Ground Reaction Force (GRF) transmission in the equine forelimb was 22 m/sec, whilst that of the hind limb suspensory system was 25 m/sec. Conclusion: Findings indicate that GRFs are transmitted proximally along the limb at considerable speeds, that they are dampened by tissues and structures in the limb, and that the GRFs are present and detectable proximal to the fetlock joint.