Measurement of Motion During Manipulation of the Equine Pelvis

Introduction Manipulation of the equine ilium and sacrum is utilised to assess range of motion at the SIJ. Motion of the ilium and sacrum during manual force application to the equine pelvis has been measured previously in vitro. The aim of this study was to measure the amount and direction of motion in vivo including comparison of bone fixated and skin mounted sensors. Methods Orientation sensors were skin-mounted over tuber sacrale (TS) and 3rd sacral spinous process (SP) of six standing Thoroughbred horses. Orientations of each TS and sacrum were recorded by one investigator during six trials of manual force applied to the pelvis, inducing cranial, caudal and oblique rotations. The study was repeated with the sensors mounted onto pins implanted into TS and SP. Mean values were reported in Euler angles for the three orthogonal planes lateral bend (LB), flexion-extension (F-E) and axial rotation (AR). Correlation between skin and bone fixated markers (Spearman R) was determined with significance set at P<0.05. Results The largest mean values recorded during rotations applied to the pelvises were for F-E (2.08 ± 0.35o) with bone fixated sensors. Axial rotation gave the largest values recorded with skin-mountings (1.70 ± 0.48o). There was poor correlation between skin-mounted and bone implanted markers. Conclusions Bony kinematics during external movement applied to the pelvis cannot be predicted from skin-mounted sensors, due to differences between skin- and bone-mounted sensors. Manipulation of the equine pelvis can be expected to produce motion in the plane of F-E, but axial movement should be interpreted with caution due to the potential effects of skin motion. Ethical Animal Research Ethical approval for animal use was obtained by the institutional animal ethics committee (University of Queensland). Sources of funding: Rural Industries Research and Development Council, Australia. Competing interests: none.