New Instrument Helps Diagnose Back Pain

Photo: Kevin Haussler's newly designed instrument -- made of a series of spinal transducers—allows scientists, for the first time, to measure the motion of individual back joints in the live horse.

Just as in humans, back pain is a common and significant problem among performance horses. Although back problems in horses have been identified as a significant cause of chronic poor performance, they are still poorly understood and therefore not recognized and treated as well as they might be.

"Back problems are often overlooked during lameness evaluations because veterinarians don't have objective measures to assess spinal dysfunction," says Kevin Haussler DVM, DC, PhD, a lecturer in biomedical sciences.

"We also have very little information about how a spinal dysfunction might affect locomotion."

Haussler says that veterinarians often have a difficult time identifying exactly where aback problem is and what caused it. As a result, most veterinarians try to relieve stiff, painful backs or muscle spasms with rest or medication, without actually addressing the cause of the injury.

Meanwhile, researchers are beginning to recognize just how prevalent the back problems might be. In a survey of 36 Thoroughbred racehorses that died of unrelated injuries, Haussler found that every horse had evidence of spinal pathology.

To better understand the effects of muscle and joint injuries on the equine back, Haussler will use a new Zweig grant to improve an instrument he helped to develop that can assess back motion. He plans to use the instrument in 10horses to determine the normal variability of thora columbar (chest and lower back) spinal kinematics (the mechanics of motion) in horses during locomotion at different gaits. And then he will investigate how the back responds to specific types of muscle and joint pain.

The grant will allow Haussler to improve upon a measuring device, which has six different gauges that measure changes in back motion. The instrument is capable of measuring three-dimensional movements: two gauges assess flexion-extension, two others measure lateral bending, and the third set evaluates axial rotation. The measuring device was used successfully in three horses in a prior study to measure the amount of back motion.

Haussler will attach the instrument with surgical screws that will be temporarily and superficially placed in the vertebrae of the back. The horses will be sedated and medicated during the surgical procedures.

In the first phase of the study, launched in May, spinal movements were measured while the horses were standing (for a baseline), walking, trotting, and cantering on a treadmill.

In the second phase of the study, Haussler will induce temporary back muscle pain or joint discomfort to simulate joint pain associated with arthritis; he will then look at the effects of muscular and articular (joint) pain on spinal motion and the functional mechanisms of acute back pain in horses.

"The induced back pain, which the horses should recover from within 10 to 15 minutes, will allow us to see how back motion changes with muscle and joint discomfort. We expect to measure reduced muscle activity and restricted back motion," Haussler explains.

To simulate the back problems, he will inject a saline solution that makes the muscles in the area temporarily spasm or abnormally tense. In one group of horses, the solution will be injected into the superficial back muscles to simulate a muscle injury. These back muscles extend between the vertebrae in the thoracic and lumbar regions and aid in the support and extension of the back. In the remaining horses, the injection will be made into the deeper back muscles near the joints to simulate an articular injury.

The amount and patterns of back motion will be compared before and immediately after the back injections. Such injections have been used before in humans to similarly measure the short-term effects of induced back muscle pain. Haussler and his collaborators will repeat the treatment and measure spinal motion one week later to evaluate the longer-term-effects of the back pain on back-movements.

"We suspect that the back pain will alter normal back and leg motion and that the superficial muscle pain will produce different changes compared to the deeper joint pain," Haussler explains.

The long-term goal of the project is not only to better understand the causes of equine back problems and their effects on locomotion and performance, but also to develop ways to objectively evaluate treatments for back problems. These might include the use of anti-inflammatory medications, muscle relaxants, physiotherapy, chiropractic, and even acupuncture modalities.