Kissing Spines in Horses: More Than Back Pain

kissing spine

Find out how veterinarians diagnose and treat this complex condition.

By Jackie Hill

In this back X-ray, note the lack of space between the spinous processes and evidence of bone bridging between some of the severely affected processes. | Photo: Courtesy Dr Jackie Hill

If you’ve ever managed a horse with back pain, then you’ve probably heard the term kissing spines floated around. But what exactly are kissing spines, and what does it mean if your horse is diagnosed with them?

Kissing spines, or overriding spinous processes, are reported to be one of the most common causes of back pain in horses. Though the back pain was originally described in the 1960s, it wasn’t until recent years that veterinarians and researchers devoted more attention to it as a primary problem in horses as opposed to secondary to hind-limb lameness. As technology has progressed to produce higher-quality X rays and our knowledge of equine back anatomy’s complexity has expanded, we have a greater appreciation for and understanding of kissing spines.

A horse’s spine is composed of individual vertebrae connected by ligaments and surrounded by muscles. Each vertebra has a bony prominence that sticks up—the spinous process. In a normal horse, the spinous processes are spaced evenly, allowing a horse to both flex and extend his back. With kissing spines, the spinous processes are too close to each other or even touching. The lack of space between processes reduces back mobility and causes pain during movement as the spinous processes interfere with each other.

The underlying cause of kissing spines is still largely unknown. The condition can occur in any horse, but some breeds, such as Thoroughbreds and Warmbloods, seem to develop it more than others. Horses are most commonly diagnosed around 5 to 10 years of age, but younger and older horses can develop it, too. Kissing spines typically occur in the last few thoracic vertebrae—right where a saddle and rider would sit along the horse’s back.

Horses with kissing spines can demonstrate a variety of clinical signs. These can be subtle, such as poor performance or decreased range of motion when asked to flex or extend the back, all the way up to more noticeable behaviours, such as a painful reaction to back palpation, reluctance to be saddled or ridden, cross-­cantering, and bucking under saddle.

Veterinarians typically diagnose kissing spines using a combination of clinical signs and X rays of the horse’s back. X rays are the best way to assess the distance between spinous processes and to look for evidence of problems in the bones, such as increased density or ­cysticlike lesions. The tricky aspect of diagnosing kissing spines is that researchers have shown that 39% of horses have changes on their back X rays consistent with kissing spines, yet they show no signs of back pain. Similarly, the angle from which the veterinarian takes the X rays can influence the apparent spacing between processes and might result in overdiagnosis.

Other diagnostic modalities your veterinarian might use include nuclear scintigraphy (bone scan), ­ultrasonography, and the injection of local anaesthetic around the suspected painful spinous processes. Unfortunately, each of these modalities has its limitations. For example, injecting a local anaesthetic into the area does not produce reliable diagnostic results, meaning veterinarians cannot predict which horses will respond to treatment. Therefore, the most reliable way to diagnose kissing spines continues to be looking at changes on back X rays in conjunction with clinical signs of back pain.

Once a veterinarian diagnoses a horse with kissing spines, he or she can proceed with several treatment options. In mild cases, horses might respond to conservative treatments such as muscle relaxants, chiropractic and acupuncture therapy, shockwave, or local corticosteroid injections. If a horse does not improve with conservative therapy or it’s a more advanced case, the veterinarian might recommend surgery. The surgical treatment might involve either cutting the ligament that runs between each spinous process at the affected sites to allow more space between them or removing part of the spinous process to create more space. The procedure the surgeon elects to perform mostly depends on the severity of the kissing spines. Surgery has been shown to produce more favourable long-term results than medical therapies in horses with this condition.

Back pain in horses can be complex. While kissing spines is the most common cause in horses, the diagnosis should not be made on X rays alone. Rather, the veterinarian should assess X rays in combination with clinical signs of back pain and only after ruling out other causes of lameness. Once your veterinarian makes a diagnosis, there are many treatment options that can help get your horse back on track and moving pain-free.

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