Understanding Kissing Spines

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Your once very agreeable horse who loved his job has picked up the habit of stopping at fences and missing changes. He seems to flinch every time you put the saddle on, so you decide to ask your vet to take a look at him to see what might be going on. After a series of questions and diagnostics, “kissing spines” is the final diagnosis. 

Also known as Dorsal Spinous Process Impingement or Overriding (ORDSP), kissing spines is the most common cause of back pain in horses. It occurs when two or more of the spinous processes are so close together that they touch or rub. As explained by Dr. Mark Donaldson of Unionville Equine Associates, it is when “bones in the back are closer together than they should be, which forms a blister.” Over time, this can form what is essentially a callus, which is why older horses may have less pain than a younger horse.

Back pain can be a product of poor conformation, lack of conditioning, mismatch of rider and horse, or chronic use of a poorly fitting saddle. Though it is most commonly seen as a change in head and neck carriage, unwillingness to bend, and overall poor performance, it can also present as a fore or hind limb lameness, change in disposition, and pain upon firm palpation.

Dr. Donaldson stresses the importance of exploring ill behavior as a result of back pain noting that, “When a horse has a foot abscess it limps, but when a horse has back pain it can manifest in a variety of ways that can be confused with other problems.”

Fortunately, a wide variety of treatments are available for this seemingly daunting condition, with both medical and surgical management options. Medical treatments are generally explored first, as they are less invasive, allow the horse to return to work faster, and are considerably less expensive. Local injections of anti-inflammatories, physiotherapy, mesotherapy, and shockwave therapy are the most common treatments for kissing spines and have shown promising results. The exact treatment—or combination of treatments—used often depends on the vet who is caring for the horse, as well as the horse’s age, stage of training, and whether or not they are competing. 

Horse’s back immediately after mesotherapy. Photo courtesy of Dr. Mark Donaldson

Injection of anti-inflammatories is used in a way which is very similar to joint injections, and is often able to make a horse more comfortable in his work for a length of time. The exact drugs which are used will vary, mainly depending on whether or not the horse will be showing, or how quickly they are expected to compete after treatment. 

Physiotherapy includes a rehab program which strengthens the horse to allow them to carry themselves better, relieving stress that was once placed on the back. This plan may include hand walking, lunging, and pole or cavaletti work, and is created in conjunction with the vet to ensure the horse is safe and comfortable. 

Mesotherapy is essentially a series of injections which prevent the nerves from deep within the back from transmitting painful messages. 

Shockwave is most commonly completed as a series of 3-4 treatments spaced 2-3 weeks apart, though as few as one treatment may be necessary. Shockwave acts as analgesic-a painkiller- and allows the damaged area to begin the healing process. 

If medical treatments fail to produce the desired results, surgical options may be explored. Though these come at a greater expense, they can produce very positive results for many horses. The most common surgical choice is Interspinous Ligament Desmotomy, which is a minimally invasive technique in which the horse stands under mild sedation and local anesthesia. It has been effective in increasing interspinous space to stop the “kissing”, eliminating the sensation of pain for the horse. A more invasive method, a Wedge Ostectomy, reduces the width of the impinging bones, therefore creating a space between the spinous processes. 

Standing lateral radiograph of the thoracic spinous process of a normal horse. The green arrows show adequate space between the spinous processes. Photo courtesy of Dr. Mark Donaldson
Standing lateral radiograph of a horse with impingement of the spinous processes (kissing spines). The red arrows show areas of impingement and sclerosis (scarring) of bone. Photo courtesy of Dr. Mark Donaldson

As with any condition, kissing spines requires maintenance work to keep your horse feeling their best. It is important to keep up with any treatments as described by your vet; however, maintenance will also depend on the severity of the condition, how much the horse’s performance is affected, and the horse’s intended use. Kissing spines can be aggravated if the horse is asked to use its back extensively, especially if they are not correctly conditioned to do so. Dr. Donaldson states that “one of the worst things for these horses is the ‘weekend warrior’ life” because it is best for horses with kissing spines to be in a consistent program. This will ensure that the horse is fit enough for the work it will be doing by strengthening the core and reducing stress on the back. 

If treated and maintained properly, kissing spines does not have to be a scary condition for you or your horse. Many horses are able to return to their career feeling more comfortable than ever. 

Haylie Kerstetter is currently attending Centenary University, where she is the captain of the Hunter/Jumper Team and is majoring in Equine Studies: Communications for the Equine Industry. She has been riding for 15 years and enjoys showing Centenary’s horses during the school year, but particularly appreciates riding Off the Track Thoroughbreds as they make their transitions to their second careers. Following her graduation, she hopes to work as a writer for equestrian-focused publications. 

Mark T. Donaldson received his Bachelor of Science from Villanova University and graduated from the University of Pennsylvania, School of Veterinary Medicine in 1993. After completing an internship at the University of Georgia he returned to the University of Pennsylvania for a residency in Internal Medicine. He is a member of the American College of Veterinary Internal Medicine. Before joining Unionville Equine Associates in 2005, he was an Assistant Professor of Medicine at the University of Pennsylvania’s New Bolton Center. He is currently a partner at Unionville Equine Associates. His clinical focus is sports medicine.  In his spare time he enjoys photography and spending time with his wife, Emily and daughter, Lucy.