Why Does My Horse Have Kissing Spine? The Science Behind the Condition.

Equine “kissing spine,” or overriding dorsal spinous processes (ORDSP), is a back issue. It occurs when the bony spikes along a horse’s spine grow too close or touch. This crowding can inflame nearby tissues and nerves, causing pain and performance issues. Kissing spine is puzzling. Some horses with concerning X-rays feel fine, while others with minor changes suffer chronic pain. . We’ll discuss why an X-ray alone can’t tell the whole story and offer practical tips for horse owners facing this diagnosis.

A Condition as Old as Time (and Not Just in Horses)

Kissing spines might seem modern, but evidence shows it has existed longer than saddles. During the last Ice Age, an extinct wild horse (Equus occidentalis) showed signs of overriding spinous processes in fossilized vertebrae. Some bones had damage similar to today’s kissing spine cases. This is surprising since those horses never carried a rider. In short, kissing spines is not new; it has likely affected spines across species for millions of years.

Humans have a similar disorder called Baastrup’s disease, or “kissing spines syndrome.” First described in 1933, this condition affects inflamed bursae between adjacent vertebral spines and often leads to low back pain. Dogs and other animals can also develop impinging spinous processes. A 2016 study at the University of Bristol looked at nearly 200 symptom-free dogs. About one-third had impinged spinous processes on X-rays, mainly between the 8th and 11th thoracic vertebrae. Importantly, these dogs showed no signs of pain or neurological issues. The authors warned vets to interpret these findings carefully, as impingement can occur often, even in animals without back pain. This cross-species view tells us two things: kissing spine isn’t just equine, and bony changes on an X-ray don’t always mean pain.

Developmental Disease or Riding Injury?

Many horse owners feel guilt or confusion, wondering if a saddle, training method, or incident caused their horse’s back problem. Research shows that riding can affect back health. However, kissing spines also have strong developmental and genetic factors unrelated to riding.

X-ray images of the mid-back (thoracic spine) in two different horses with kissing spines. Left: A 20-month-old Thoroughbred colt that had never been ridden shows severe crowding and “kissing” of the spinous processes from T12 to T17. Right: A 20-year-old Thoroughbred mare, retired from racing and jumping, has similarly severe kissing spine lesions from T15. These cases show that even young horses can develop significant kissing spine changes before any ridden training, pointing to factors beyond just riding (from Pressanto, M.C. et al. 2023).

A 2023 study at the University of Perugia tested the riding causes theory. Researchers compared two groups of Thoroughbreds: 47 unbroken yearlings and 55 trained horses. All were reportedly free of obvious back pain. Every horse underwent a full spinal radiograph series to check for impinging spinous processes. The result? Young horses straight out of the pasture had just as many kissing spine lesions as adult athletes. There was no significant difference between yearlings and older horses. Narrowed interspinous spaces and impingements were found in about one-third of the examined areas. Additionally, more than half of the yearlings showed some bony changes in their dorsal spines. The authors concluded this points to a developmental cause for kissing spines. In other words, many horses likely develop this condition as they grow, not simply due to wear-and-tear from riding.

These findings align with what some vets have noticed: some young horses seem more likely to get kissing spines, even with little handling. Conformation matters. Horses with short backs or “shark-fin” withers may have spinous processes that are angled or close together, increasing their risk of impingement. Breed statistics suggest a hereditary link: Thoroughbreds, Warmbloods, Quarter Horses, and Paints are more common in kissing spine cases. Many of these are tall, athletic breeds, and one study noted the condition is more prevalent in larger horses.

Can We Prevent Kissing Spine?

Maybe, one day. In 2022, geneticists found a specific gene variant linked to kissing spine. This supports what breeders suspected: there is a heritable component. It opens the door for future genetic tests or selective breeding strategies. As one researcher noted, the identified gene isn’t the sole cause but is a step forward in understanding spinal cartilage cell growth. None of this means that riding and management are off the hook. Environmental and mechanical factors still impact whether a horse with latent kissing spine feels pain. The research team for the yearling study noted that kissing spine is a complex orthopedic disease. Factors like genetics, growth rate, and early-life nutrition play a role. A horse can be born with narrow interspinous gaps or weak muscles. As it grows, these bony processes may crowd together. Then, acquired factors like hard work, poor saddle fit, or inappropriate training can worsen the condition or trigger pain. Repetitive strain and trauma also have an effect. Athletic performance horses experience high stress on their mid-backs, especially during jumping. Some researchers believe this mechanical overload can worsen impingements over time. So while riding didn’t create the bone changes in a 2-year-old, it can certainly aggravate early lesions. Think of genetics and development as loading the gun, and lifestyle as pulling the trigger. This explains why we see it across various horses, from pasture pets to top competitors.

When Kissing Spines Don’t Hurt (and When They Do)

One puzzling aspect of kissing spine syndrome is the inconsistent link between X-rays and how the horse feels. Vets often find overlapping spines on radiographs, yet the horse moves soundly. Conversely, a horse in pain might have only mild narrowing on X-ray. This disconnect between lesions and pain is well-documented and poses a diagnostic challenge.

Why would bony impingement hurt one horse and not another? Pain likely arises not from the bones touching, but from inflammation of nearby ligaments, muscles, and nerves. In people with Baastrup’s disease, the rubbing of spinous processes causes bursitis and damages the ligament between the spines. In horses, we think a similar thing happens. When the tips of the dorsal spines touch, the interspinous ligament can become inflamed or partly torn. This can lead to nearby muscles spasming due to ongoing soreness. If the impingement is slight or if the horse has strong musculature, there may be minimal inflammation and pain. Compensation and individual pain tolerance also play roles. Some horses change their movement to ease pressure from a pinched area. They also have different levels of discomfort. Certain impingements might occur in less sensitive areas, while a small lesion in a bad spot could cause significant pain.

Interestingly, kissing spine pain can come from changes beyond just the bones and local tissues. A 2020 Malaysian study examined the spinal cords of horses with long-term back pain and kissing spine lesions. Their analysis found damage and inflammation in the spinal cord likely due to constant pain signals. The horses’ thoracolumbar spinal cord segments showed bleeding and damage under a microscope. There was also a reactive overgrowth of support cells. The horses’ nervous systems changed due to chronic pain. This is similar to what happens in humans with long-term injuries. This central hypersensitization may explain why some severe kissing spine cases are tough to treat. The problem isn't just a local "sore spot." It becomes embedded in the nervous system's pain pathways.

To assess a horse for kissing spine, we need a holistic approach. The link between lesions and pain is complex. A vet will connect clinical signs to imaging results. They often do diagnostic blocks to check if the pain comes from the spines pressing on nerves. It’s not always straightforward. Many horses with kissing spines also have other back problems, like arthritis in facet joints or muscle strain. This complicates diagnosis. Diagnosis becomes a process of elimination and synthesis. Owners should remember that an X-ray is just one piece of the puzzle. Don't panic if your horse's radiographs show impinging processes. Take it seriously. Work with your vet to interpret the images based on your horse’s performance and behavior.

Practical Advice for Horse Owners

If your horse has kissing spines, it’s normal to feel worried, relieved, or uncertain about the future. The good news is many horses with this condition can be managed well. Some even return to high performance with the right treatment. Here are a few key tips based on veterinary experience and research:

1. Watch for subtle signals. Horses often hide pain well, so signs of discomfort can be subtle. Notice any changes in behavior: Is your horse reluctant to canter or jump? Are they swishing their tail, pinning their ears when saddled, or hollowing their back under saddle? These could signal spinal discomfort. Don’t dismiss them as “bad attitude.” Early intervention can greatly improve outcomes, so have a vet check your horse before the pain worsens.

2. Get proper diagnostics. If kissing spines are suspected, start with quality X-rays of your horse's back, but don’t stop there. Work with an equine veterinarian, preferably a specialist, to conduct a thorough evaluation. This may include ultrasounds of the ligaments or numbing injections to confirm painful areas.

3. Commit to long-term rehabilitation. Whether your horse undergoes shockwave therapy, corticosteroid injections, surgery, or simply conservative management, a structured rehab and conditioning program is key. The goal is to strengthen your horse’s core and back muscles, encouraging them to move in a posture that unloads the impinged areas. This often involves months of groundwork, stretching exercises, and gradual return to ridden work with an emphasis on proper carriage. It’s not a quick fix, but many owners report their horses come out stronger and more comfortable than before. Think of it as an opportunity to rebuild your horse’s back from the ground up.

4. 4. Optimize the horse’s environment and equipment. Make sure your saddle fits impeccably, consult a professional saddle fitter, as even a high-quality saddle can cause issues if it doesn’t match your horse’s shape. Turnout and the ability to move freely are important; movement helps keep the back supple. Some horses benefit from specialized shoeing or hoof trims to ensure their posture isn’t negatively affecting the back. Look at your horse’s diet as well: since developmental bone health is tied to nutrition, ensure youngsters get a balanced diet with appropriate calcium, phosphorus, and other minerals. Avoid overfeeding foals and yearlinds, as rapid weight gain can stress growing bones.

   
   

If you’re seeing some of these signs in your horse, or you simply want a more complete understanding of their back health, now is the perfect time to take the next step. Many horses with kissing spines go on to live happy, productive lives. A thorough chiropractic and acupuncture evaluation can bring clarity, comfort, and a clear plan forward.

Book an appointment with The Zen Vet to give your horse the comfort, mobility, and long-term support they deserve.

Sources:

1. Pressanto, M.C. et al. (2023). JAVMA 261(6):844-851. Radiographic vs. clinical findings in yearling vs. adult Thoroughbreds with “kissing spines”.

2. Thierry, F. et al. (2016). J. Small Anim. Pract. 57(12):698-702. Prevalence of impinged spinous processes in asymptomatic dogs

3. Mayaki, A.M. et al. (2020). J. Equine Vet. Sci. 90:103019. Spinal cord changes (microgliosis, astrogliosis) in horses with chronic back pain and kissing spines

4. Klide, A.M. (1989). Am. J. Vet. Res. 50(4):592-593. Fossil evidence of overriding spinous processes in an extinct wild horse (Equus occidentalis)pubmed.ncbi.nlm.nih.gov.

5. Lesté-Lasserre, C. (2022). The Horse. Report on genetic study linking a Chromosome 25 variant to kissing spine severitythehorse.comthehorse.com.

6. MDPI (2025). Animals 15(18):2679. Narrative review of impinging/overriding dorsal spinous processes in horsesmdpi.commdpi.com.

7. Physio-Pedia. Baastrup Syndrome (“kissing spine” in humans) – overview of pathology and risk factors