The Effect of Chiropractic Treatment on Biomechanical Imbalances and Pain Response in Horses by Taylor Prichard A THESIS Submitted to Oregon State University Honors College in partial fulfillment of the requirements for the degree of Honors Baccalaureate of Science in Biology (Honors Scholar) Presented December 4, 2019 Commencement June 2020 AN ABSTRACT OF THE THESIS OF Taylor Prichard for the degree of Honors Baccalaureate of Science in Biology presented on December 4, 2019. Title: The Effect of Chiropractic Treatment on Biomechanical Imbalances and Pain Response in Horses Abstract approved: ______________________________________________________________ Katja F. Duesterdieck-Zellmer Chiropractic treatment is used to reduce stiffness and pain. While more thoroughly studied in humans, it has been shown to be effective in horses, but relatively little evidence exists to quantify the benefits. To address this shortcoming, four methods were used to assess the effects of chiropractic treatment in horses in this study. Pressure algometry was used to assess pain by applying pressure at predetermined landmarks, proximately 10 cm lateral to the midline. The Lameness Locator was used to assess lameness by applying three sensors to the horse to determine relative asymmetry of the poll and croup. Video analysis was used to quantify performance by measuring the hock amplitude throughout the stride as an approximation for hock flexion, and gait evenness was measured by comparing diagonal limb pairs in the trot when the limbs were fully extended. Finally, owner surveys were used to assess general attitude, soreness and willingness to perform. Manually applied chiropractic treatment was effective at increasing mechanical nociceptive thresholds and quality of gait at a trot 6-8 days after treatment. However, it does not appear as though lameness, as detected by the Lameness Locator, changed 6-7 days post-treatment. Furthermore, the owner survey also revealed that owners did not notice a significant change in their horses’ attitude, appetite, soreness, swelling, willingness to perform under saddle or on the ground in hand. Key words: equine, chiropractic, spinal manipulation, gait analysis, lameness locator, pressure algometry Corresponding email address: [email protected] ©️Copyright by Taylor Prichard December 4, 2019 All Rights Reserved The Effect of Chiropractic Treatment on Biomechanical Imbalances and Pain Response in Horses by Taylor Prichard A THESIS Submitted to Oregon State University Honors College in partial fulfillment of the requirements for the degree of Honors Baccalaureate of Science in Biology (Honors Scholar) Presented December 4, 2019 Commencement June 2020 Honors Baccalaureate of Science in Biology project of Taylor Prichard presented on December 4, 2019 APPROVED: ______________________________________________________________________________ Katja F. Duesterdieck-Zellmer, Mentor, representing Department of Clinical Sciences ______________________________________________________________________________ Jacob A. Mecham, Committee Member, representing Department of Clinical Sciences ______________________________________________________________________________ Stacy Semevolos, Committee Member, representing Department of Clinical Sciences ______________________________________________________________________________ Toni Doolen, Dean, Oregon State University Honors College I understand that my project will become part of the permanent collection of Oregon State University, Honors College. My signature below authorizes the release of my project to any reader upon request. ______________________________________________________________________________ Taylor Prichard, Author Acknowledgements I would like to thank my mentor, Dr. Zellmer, for her continued support throughout the entirety of this project, and her willingness to step up to the task of becoming my mentor when the situation arose. This project wouldn’t have been possible without her patience and guidance. Thank you to Dr. Mecham, who agreed to take on this project despite his limited time and experience with research. This was my first introduction to both research and the clinical side of chiropractic care, and I appreciated learning from someone so compassionate. Thank you to Dr. Kutzler, who helped organize the beginning phases of this project. Without her support, this project likely would have never begun. Thank you to Kim Veldman, Sofia Vega and Kuilei Kramer for helping with data collection. I don’t know how we would have done so much in such a short period of time without their help. Thank you to the OSU Department of Clinical Sciences for allowing the use of equipment that made data collection possible for this research. Thank you to Summer Undergraduate Research Experience (SURE) for funding my work over the summer. Table of Contents Introduction……………………………………………………………………………………………………………………………………..……1 Literature Review……………………………………………………………………………………………………………………………..……2 History of Chiropractic Adjustments.……………………………………….………………………………………………..2 Application of Chiropractic Care………………………………………………………………………………………………..3 Pressure Algometry…………………………………………………………………………………………………………………..6 Lameness Locator……………………………………………………………………………………………………………………..7 Assessment of Gait Quality……………………………………………………………………………………………………….9 Objectives and Aims…………………………………………………………………………………………………….………………………..15 Materials and Methods…………………………………………………………………………………………….……………………………11 Horses………………………………………………………………….……………………………………………………………………11 Experimental Set-up.………………………………………………………………………………………………………………..12 Treatment………………………………..……………………………………………………………………………………….……..13 Mechanical Nociceptive Thresholds………………………………………………………………………………..………..14 Lameness Locator……………………………………………………………………………………………………………………..16 Analysis of Hock Angle and Stride Symmetry…..………………………………………………………………………..19 Owner Survey……………………………………………………………….…………………………………………………………..22 Statistical Analyses…………………………………………………………………………………………………………………...22 Results…………………………………………………………………………………………………………………………………………………..24 Treatment…………….…………………………………………………………………………………………………………………..24 Pressure Algometry…………………………………………………………………………………………………………………..25 Lameness Locator……………………………………………………………………………………………………………………..30 Video Analysis…………………………………………………………………………………………………………………………..32 Owner Survey……………………………………………………………………………………………………………………………36 Discussion……………………………………………………………………………………………………………………………………………..41 Conclusion…………………………………………………………………………………………………………………………………………….48 References…………………………………………………………………………………………………………………………………………….49 Abbreviations………………………………………………………………………………………………………………………………………..57 Appendices……………………………………………………………………………………………………………………………………………58 Appendix 1: Horse Variability………………………………………………………………….………………………………..58 Appendix 2: Treatment……………………………………………………..………………………………………………………60 Appendix 3: Pressure Algometry…………………………………………………..…………………………………………..62 Appendix 4: Lameness Locator………………………………………………………………..………………………………..83 Appendix 5: Gait Analysis………………………………………………………………………………..………………….…….84 Appendix 6: Owner Survey…………………………………………………………………………..……………………………90 Appendix 6: Owner Survey Data .………………………………………………………………..……………………………91 Table of Figures Figure 1 – Joint mechanics relating to the active and passive range of motion of the joint (Haussler 2010)…………………………………………………………………………………………………………………………………………………….…4 Figure 2 – Approximate location of pressure algometry readings marked by blue circles………………………15 Figure 3 – Location of lameness locator sensors (Equinosis LLC 2017)………………………………………..…………17 Figure 4 – Determination of forelimb lameness using data from the Lameness Locator…………………………18 Figure 5 – Determination of hindlimb lameness using data from the Lameness Locator……………….………19 Figure 6 – Scaling of video for analysis…………………………………………………………………………………………………..21 Figure 7 – Determining hock amplitude…………………………………………………………………………………………….…..21 Figure 8 – Determining stride evenness………………………………………………………………………………………….……..22 Figure 9 – Pressure Algometry (Pooled measurements from left and right sides for all horses)………….…26 Figure 10 – Difference in Pressure Algometry Readings (Pooled measurements from left and rights sides for all horses)……………………………………………………………………………………………………………….……………………..…27 Figure 11 – Pressure Algometry (Pooled measurements from left and right sides for last nine horses)...28 Figure 12 – Difference in Pressure Algometry Readings (Pooled measurements from left and rights sides for the last nine horses)…………………..………………………………………………………………………….……………………..…29 Figure 13 – Hock amplitude (Pooled measurements from left and right sides for all horses, normalized to horse height)……………………………………………………………………………………………………………………….…………..……32 Figure 14 – Difference in Hock Amplitude (Pooled measurements from left and right sides for all horses, normalized to horse height)………………………………………………………………………………………………..…………..……33 Figure 15 –Gait Evenness (Pooled measurements from left and right sides for all horses, normalized to horse height)………………………………………………………………………………………………………………………………………...34 Figure 16 – Difference in Gait Evenness (Pooled measurements from left and right sides for all horses, normalized to horse height)………………………………………………………………………………………………..…………..……35 Figure 17 – Owners’ perceived change in attitude after chiropractic treatment compared to before treatment………………………………………………………………………………………………………………………………………..……36 Figure 18 – Owners’ perceived change in appetite after chiropractic treatment compared to