The multifidus muscles, a series of overlapping muscle bundles in a horse’s back, play a significant role in stabilizing segments of the horse’s spine, which is important for countering daily destabilizing forces. Horses with back pain commonly experience atrophy and dysfunction of the multifidus muscles and, therefore, reduced flexion and extension of the spine, as well as decreased lateral (side-to-side) flexion.

“Osseous pathology can cause loss of the multifidus muscle size, resulting in pain, instability, and weakness,” said Melissa King, DVM, PhD, Dipl. ACVSMR, associate professor of equine sports medicine and rehabilitation at Colorado State University, in Fort Collins. She presented on the subject at the inaugural American College of Veterinary Sports Medicine and Rehabilitation conference, held April 27-29 in Charleston, South Carolina. “Evidence in people demonstrates that smaller cross-sectional area of the multifidus muscle in the lumbar spine increases the risk for distal (lower) limb injury, and similar results may occur in the horse.”

Study results have shown that 74% of horses with back pain exhibit limb lameness, while 32% of limb-lame horses also experience back pain, King added. In a study of horses presenting with unilateral (one-sided) fore- and hind-limb lameness, researchers saw a direct correlation between forelimb lameness and multifidus muscle atrophy bilaterally (on both sides) at multiple spinal levels in the thoracolumbar region (the part of the spine that runs from the withers to the pelvis), and many horses had signs of long-term multifidus muscle adaptation in relation to chronic lameness.

Multifidus muscle atrophy can lead to poor core strength, which often causes inappropriate balance, poor performance, and increased risk of injury, said King. “Targeting the multifidus muscles during recovery can reduce the rate of re-injury in people and would be expected to have similar results in the horse.”

Cervical (neck) dynamic mobilization exercises, such as carrot stretches, can help increase multifidus muscle size, said King. Controlled exercise in an elastic resistance band system can help improve thoracolumbar dynamic stability and, as the horse progresses to ridden work, adding gymnastics to the horse’s routine builds the multifidus muscles and increases stride length, she added.

“Neuromuscular stimulation (which uses low-level electrical current to allow contraction of specific muscle groups) combined with elastic bands might also help to increase the multifidus muscle,” said King. Using these exercises to increase core strength and multifidus muscle size increases the horse’s chance of a successful rehabilitation and, if continued, potentially decreases the risk of re-injury.