The Harry M. Zweig Memorial Fund for Equine Research

Back Motion in Horses During Different Gaits:
Effects of Back Injuries

Dr. Kevin Haussler

Back problems are an important and prevalent cause of poor performance in horses. Unfortunately, little is known about how back pain, muscle spasms or restricted back motion affects horses. Therefore, back problems are often overlooked during lameness examinations due to vague signs or poorly understood effects on locomotion. Studying back motion in horses is necessary to expand our understanding of the complex structural and functional interactions normally present. Knowledge of how the back moves is also important for investigating the effects of back injuries. Because a high prevalence of back problems has been reported in performance horses, the focus of this study is to understand the effects of muscle and joint injuries on the back. Direct knowledge of normal and abnormal back motion during different gaits and activities will expand our understanding of the basic causes of back injury in horses. In addition, information from this study will help veterinarians to develop recommendations for rehabilitation and prevention of back problems. The objective of this study is to directly measure three-dimensional back motion in horses and to investigate the effects of pain on back motion.

Our study is divided into three separate portions and we plan to:

1) modify and improve an instrument used to measure back motion in horses that was developed and tested in a prior study (Appendix 1 and 2);
2) determine the normal ranges of back motion in normal horses during different gaits; and
3) investigate how the back responds to specific types of muscle and joint pain.

Previously, we developed and tested a unique instrument for measuring back motion in horses. In this project, we will modify and improve this instrument (Part 1) and use it to comprehensively determine the normal amount and patterns of back motion in horses during different gaits (Part 2). The main focus of this project is to investigate how the back responds to specific types of muscle and joint pain and their effects on back motion and locomotion (Part 3). Ten horses will be used in this study. Surgical screws will be temporarily placed superficially in the vertebrae of the back. A measuring device will be attached to the bone screws which will measure the amount of back motion. This technique was used in a prior study in our laboratory and is used in humans and dogs to measure back motion. Normal back motion will be measured at a walk, trot and canter on the treadmill. The final portion of the project will involve injecting small amounts of a saline solution into the back muscles to produce temporary back muscle discomfort or near the joints of the back to simulate joint pain associated with arthritis. We will test to see how back motion changes due to muscle and joint discomfort. The expected results include reduced muscle activity and restricted back motion. The saline solution has been used before in human patients to measure the short-term effects of induced back muscle pain. The horses are expected to recover from the induced back pain within 15 minutes. One week later, a second treatment and associated measurements will be repeated for evaluating either the muscle or joint pain. Comparisons will be made in the amounts and patterns of back motion before and immediately after the back injections. We propose that back pain will alter normal back and leg motion and that back muscle pain will produce different changes compared to joint pain. The long term goal of this project is to understand the causes back problems in horses and their effects on locomotion and performance. Information from this project will also provide needed and relevant information on how to treat and prevent back problems in horses.