IMAGING ADVANCEMENTS APPLIED TO THE AXIAL SKELETON
Thank you for the positive response to our offer of discounted “Farrier” radiographs last month. It’s a reminder of how much we appreciate our client's attentiveness to the finer points of horse health management and your interest in learning “new tricks” as technology advancements bring new and improved veterinary applications. We also appreciate local farriers, eager to learn and apply insights revealed by radiographic imagery to fine tune their podiatry skills.
Staying with the subject of imaging advancements, let’s expand the conversation to include subtleties of lameness pertaining to the equine axial skeleton, specifically problems in the neck and back. As you may recall, equine structural anatomy can be divided into two main functional components, the appendicular and the axial skeleton. The appendicular portion of the skeleton refers to the appendages, including the limbs, the feet, the scapula and the pelvis. The axial skeleton makes up the core of the body, it includes bones of the skull, the spine, rib cage and sternum. Radiography is commonly used to evaluate the appendages, but in the not-so-distant past, it was limited for visualization of the axial skeleton. It required large, heavy machinery and often a horse under anesthesia to adequately image the skull or spine. With the advent of powerful digital radiographic tools and techniques, we can now visualize many parts of the axial skeleton in the standing horse, without need for referral or hospitalization.
The adage, “no foot, no horse” is common knowledge, but equally important, relative to soundness, is the axial skeleton or core of the horse. Problems with the axial skeleton can often be subtle and challenging to diagnose. Signs may range from intermittent lameness, to mild changes in gait, resistance to training or may even manifest as behavioral problems. A thorough physical and performance evaluation with radiography of the neck and back can be just what the doctor orders for a horse with performance limiting issues.
WHEN A PAIN IN THE NECK IS MORE THAN JUST A MARE IN SEASON
One relatively common problem for performance horses is neck pain. A complex group of muscles, ligaments and fascia support the 7 large cervical vertebrae of the horse. The vertebrae do a lot of heavy lifting, acting as cantilever for the heavy skull. They are the conduit for the spinal cord and a myriad of nerves exit their bony casing to extend down into the forelimbs and chest. With the kind of shenanigans that horses can do at liberty or in the cross ties and with the demands we make on them for performance, (collection, quick turns, jumping) it doesn’t come as a big surprise that they may develop pain in their neck. The design of the cervical vertebrae allow for considerable range of motion, flexion, extension and some lateral movement which gives the neck its flexibility. Over time, with the wear and tear of life, due to one big trauma or due to many small ones, the joints between these vertebrae (cervical facets) can develop osteoarthritis. Signs of pain from degenerative osteoarthritis can be quite varied, from obvious stiffness, to a subtle change in attitude or willingness to work. It can present as a front limb lameness, poor performance or unusual resistance to the bridle. Both radiography and ultrasound are useful tools to diagnose cervical facet arthritis.
WHEN A KISS IS MORE THAN JUST A KISS
Another abnormality that affects the axial skeleton is impingement of the dorsal spinous processes of the vertebrae, or “kissing spines”. Overriding spinous processes are most often problematic in the thoracolumbar region of the back (most frequently T13-T18). The diagnosis can be made using radiographic imaging. Number of vertebra involved and what the horse does for a living may determine whether or not impingement is associated with back pain. (Higher incidence of disease in dressage and jumping horses.) The occurrence of kissing spines is thought to be related to conformation and development and while it does not always appear to cause back pain, kissing spines should be considered a predisposing factor. Signs of back pain are often highly variable and by the time a veterinarian becomes involved, the horse has made some compensations for the discomfort making it a challenge to determine one discrete source of pain. (see case report in our
March 2018 newsletter
.) Treatment for painful kissing spines is designed to reduce pain, induce muscle relaxation and eliminate contributing factors, like poor saddle fit. Exercises that encourage a “long and low” frame, stretching and strengthening the back are often effective for long term management.
These are radiographs of two different horses thoracic spines, taken caudal to (behind) the withers. (Horse's head is to the left.) One image shows normal anatomy, can you find the one with evidence of "kissing spines"? Below is an articulated equine skeleton showing the thoracic spine for reference.