When a horse shows signs of poor performance, rearing or bucking under saddle, sensitivity when grooming, and being cold-backed, the owner often jumps to the conclusion that he has a sore back. When is an issue truly back pain, however, and when is it secondary to another orthopedic issue?
Andrew Fiske-Jackson, BVSc, MVetMed FHEA, Dipl. ECVS, MRCVS, senior lecturer in equine surgery at the Royal Veterinary College’s Equine Referral Hospital, in the U.K., tried to answer this question during the 2018 British Equine Veterinary Association Congress, held Sept. 12-15, in Birmingham.
When diagnosing back pathology in horses, there is no gold standard test or objective system of quantifying that pain, he said. “It’s as much about ruling things out as it is in.”
Diagnostic limitations include the horse’s large size in comparison to imaging machines and the cost to the owner of running those tests.
Often, said Fiske-Jackson, what manifests as a “sore back” is actually secondary to a fore- or hind-limb lameness. He explained that forelimb lameness can change the kinematics (movement) of the thoracolumbar (upper back) region, and the increased head movement at the trot associated with that lameness can also affect the cranial thoracic vertebrae—about where the saddle sits. Hind-limb lameness reduces the range of motion in the lumbosacral (lower back) region, the site where most movement normally occurs.
“Seventy-four percent of horses with back pain are also lame,” said Fiske-Jackson. “Resolve the lameness first.”
Then, he said, the veterinarian can use diagnostic analgesia to “block” the back and spinous processes and assess the horse’s response. For rider safety reasons, said Fiske-Jackson, he uses a weighted surcingle, rather than a person, to compare the horse’s response to blocking.
The next challenge, he said, is measuring back movement and pain objectively. He noted that optical motion capture (using markers on the horse’s body and high-speed cameras) has historically been the gold standard for assessing 3-D back movement and orientation in horses, but it’s not practical for use in the field.
It’s more feasible, he said, for veterinarians to use inertial measurement units (IMUs, lightweight sensors placed on the horse’s body, pictured below) to gather repeatable data in a horse’s normal environment. These “show acceptable accuracy and good levels of consistency for assessment of back movement,” Fiske-Jackson said. Using these sensors, researchers have determined that horses with back pain show reduced movement between the withers and pelvis.
Another indicator of back pain is muscle asymmetry. In humans with back pain, for instance, atrophy (muscle wasting) occurs very quickly—even within days—he said.
Fiske-Jackson has studied the multifidus muscles (located around the vertebral column) of 11 horses with impinging spinous processes (kissing spines) and found the multiple asymmetries correlated with the grade of impingement.
In summary, he said, lameness affects back movement—address this first. Veterinarians can then use IMUs to measure back movement and ultrasound to measure muscle asymmetries.