Back pain in horses has always been a difficult diagnosis because it is hard to get any objective data on the horse’s back. However, Dr. Cooper Williams said at the AAEP Convention that equine practitioners should be using ultrasound to further examine the muscles in the horse's back. Almost all equine practitioners have access to an ultrasound with sufficient power to image the equine back muscles and can diagnose specific conditions in this area. The multifidus muscle is the major muscle in the horse’s back. It is not a single muscle, but a group of overlapping muscles grouped into five distinct bands. Each muscle originates at the end of a spinal vertebrae and spans two to four vertebrae and it is likely that injuries to these muscles are underdiagnosed. Because these muscles are deep and adjacent to the vertebrae, examining them by palpation, X-rays and even bone scanning is not very effective.
Many of these horses have atrophy of the back muscles and spasms and these muscles can be examined thoroughly with ultrasound. All of the muscles in the back should be examined with ultrasound. It requires measuring the size of the muscles and comparing results to the same muscles on the other side to know if there is a problem, so this procedure does require some time and experience. Changes noted on ultrasound may be the size and shape of the muscles, a decrease in shade of the image, which can indicate a tear in the muscle or injury, and an increase in muscle shade that can indicate inflammation where the muscles are attached to the bone. So, if you have a horse with a suspected back problem causing decreased performance, ask your veterinarian about an ultrasound exam.