By Christa Lesté-Lasserre
If we’re observant, and we have the science behind our investigations, we can better determine the reason for lameness based on how a horse is lame. And, said a French researcher, we’re one step closer to characterizing neck-related lameness associated with osteoarthritis (OA) and related nerve impairment.
“A lot of times when we can’t find the source of pain in the limbs, we just have to start looking for other sites with expensive imaging exams,” said Gwenola Touzot-Jourde, DVM, PhD, Dipl. ACVAA, ECVAA, a veterinary anesthesiologist at Oniris Nantes-Atlantic National College of Veterinary Medicine, Food Science and Engineering. “But if we could recognize signs of lameness that are typical of certain conditions like cervical joint degenerative diseases, we could better determine which cases are more likely to need attention to this particular area.”
Touzot-Jourde sought to better understand lameness associated with OA in the C6-C7 cervical vertebrae—a site known for nerve compression due to bone disorders (especially articular process joint arthropathy). That’s why she and her fellow researchers chose to experimentally create nerve root dysfunction at the level of C6-C7 vertebrae in four healthy French Trotters and then observe how it affected their gaits.
“This is a very focused part of the lower neck, and it’s a difficult area to navigate,” she said during her presentation at the 15th annual conference of the International Society for Equitation Science (ISES), held Aug. 19-21 in Guelph, Ontario, Canada.
“The featured area has articular processes that form two articular process joints on either side of the adjacent vertebral bodies,” Touzot-Jourde said. “These bodies are very interesting because they allow a lot of rotational movements to the cervical spine, but they can also end up receiving a lot of stress in ridden horses (due to various influences of the rider and exercises).”
Repeated stress on joints can lead to the development of OA, she added.
Osteoarthritis in the C6-C7 joint can cause compression on the seventh cervical nerve, which is associated with shoulder and foreleg sensation, she said. This compression isn’t to be confused with spinal cord compression, which causes hind-limb weakness and ataxia (incoordination) typical of wobbler’s syndrome, for example.
To demonstrate the kind of lameness associated with seventh cervical cord compression at the C6-C7 joint, Touzot-Jourde and her fellow researchers temporarily anesthetized this nerve root in their four study horses. They identified the nerve, guided the injection process by ultrasound, then used contrast radiography (X ray with a special dye) to identify local anesthetic diffusion in the tissue.
They found that these horses had shortened strides and tightened gaits, Touzot-Jourde said. The horses also tended to exhibit a general lack of shoulder tone. “It’s like the shoulder wasn’t stuck to the body anymore,” she said. The horse would swing its shoulder out laterally and keep it deviated out while standing and would place the foot too far out to the side while stepping at the walk. The clinical signs were similar to a motor impairment of the suprascapular nerve known as “Sweeney shoulder.”
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