Kissing Spines in Sport Horses: What the Radiograph Can't Tell You

Few phrases end a vetting faster than "kissing spines." The radiographs come back, the veterinarian points to two spinous processes sitting too close together under the saddle, and a buyer who was ready to wire the money starts asking about the next horse on the list. Owners hear the same words at the end of a poor performance workup and, sometimes, hear a surgical recommendation in the same breath. The research on this condition is now deep enough to say something firm about both moments. The film alone should decide neither.

A Finding Before It Is a Diagnosis

The term describes the dorsal spinous processes of the thoracic and lumbar vertebrae, the bony fins that rise from the spine beneath the saddle, crowding, touching or overlapping. A 2025 narrative review in the journal Animals, written by researchers at the University of Camerino and the Sports Horse Research Center at the University of Perugia, sets the working definition at an interspinous space narrower than 4 mm (0.16 in), and notes that Warmbloods, Thoroughbreds and Quarter Horses appear particularly susceptible.

The difficulty is that horses with no back trouble at all routinely meet that definition. At the Norwegian School of Veterinary Science, a team led by C. Erichsen radiographed and scanned the backs of 33 apparently normal riding horses for a 2004 study in the Equine Veterinary Journal. Only 11 of them had normal spacing between the spinous processes, wider than 4 mm (0.16 in), and only 7 had no scintigraphic or radiographic findings whatsoever. The authors concluded that changes within the range they found in normal horses cannot be interpreted as clinically significant when they turn up in a horse with a complaint.

A much larger clinical study points the same way. Researchers at the Animal Health Trust in Newmarket examined 582 horses presented for suspected back pain and poor performance, with nerve blocks of the limbs, back and sacroiliac region alongside radiography and scintigraphy. Radiographic grade was associated with back pain, but horses with arthritis of the small joints between the vertebrae were more likely to be painful than horses with spinous process lesions alone, and limb lameness or sacroiliac pain could mimic a sore back. Their conclusion was blunt: diagnostic analgesia is crucial for an accurate diagnosis. More than a decade later, the Italian review reached the same place, reporting that a definitive cutoff grade separating a sound horse from one with clinical disease has yet to be established, and suggesting that such a cutoff may never exist.

A narrowed space on a radiograph tells a buyer where to look, and on its own it says very little about whether the horse is in pain.

The Case for the Scalpel

The surgical argument deserves its full weight, because it rests on real data. In 2012, Richard Coomer and colleagues at Cotts Equine Hospital in Wales published a controlled case series in Veterinary Surgery comparing interspinous ligament desmotomy, a minimally invasive procedure performed on the standing, sedated horse, with corticosteroid injected directly into the affected spaces. Every horse followed the same controlled exercise plan. Initially, 34 of the 38 medically treated horses (89 percent) and 35 of the 37 surgical horses (95 percent) showed resolution of back pain. The difference came later: back pain returned in 19 of the medical cases and in none of the surgical ones, and horses that had the surgery were 24 times more likely to achieve long-term resolution.

Racing data add an objective outcome. A 2019 study in The Veterinary Journal, from University College Dublin, Fethard Equine Hospital and the University of Tennessee, followed 159 Thoroughbreds that had the same desmotomy and compared their race records with matched controls of the same age and sex, trained by the same trainers at the same time. The operated horses improved significantly more than their controls. A broader owner survey of 260 ridden horses, led by Rebecca Brassington at University Centre Bishop Burton and published in Equine Veterinary Education, found that horses treated surgically had twice the odds of returning to their previous level of performance compared with horses that were not.

Where the Evidence Thins

Each of those studies carries a limit that the enthusiasm around the surgery tends to skip. The Coomer series was retrospective and the horses were not randomized to treatment. The Bishop Burton data came from owners recruited through social media, a design its authors acknowledge is open to self-selection and recall bias. None of the outcome studies described here randomized horses to treatment, and none was a trial in ridden sport horses designed to compare surgery, medication and rehabilitation head to head.

The procedure is also not free of consequence. Eight of the 159 racehorses in the Dublin study developed one-sided neurogenic atrophy of the back muscles after surgery. In a 2021 review in the Equine Veterinary Journal, the same Dublin group, with colleagues from Tennessee and the Royal (Dick) School of Veterinary Studies in Edinburgh, proposed that a branch of the dorsal spinal nerve supplying the longissimus muscle was the likely casualty, and warned that the literature on the neuroanatomy of the equine back is thin even though local anesthesia, medication and surgery in the region are relatively common.

The clearest sign that the field has not converged comes from the veterinarians themselves. When a team at the Freie Universität Berlin surveyed 353 equine orthopedic specialists for a 2024 paper in Veterinary Record, the authors report that 71 percent preferred conservative management, reserving surgery for horses that failed to respond. Surgery as a first-line treatment was recommended mainly by specialists in the United States, the United Kingdom and Ireland, and manual therapy was on the table for 42 percent of European specialists against 25 percent of American ones. The authors concluded that treatment is shaped by professional specialization and regional preference. Put plainly, the plan a horse receives can depend on which side of the Atlantic it is examined.

The Variable That Matters Most

The most striking number in the recent literature has nothing to do with a scalpel or a needle. In the Bishop Burton survey, 49.6 percent of horses returned to their previous level of performance, and horses whose owners described a tailored exercise rehabilitation plan had 10 times the odds of doing so. That group emerged from write-in answers rather than a predefined category, so the figure is a signal worth testing rather than a settled effect size, but it is a large one. Horses with at least one additional musculoskeletal problem, reported in 60.8 percent of the sample and most often involving the hocks or the sacroiliac region, fared worse: 43.7 percent returned to level, against 58.8 percent of horses with no second diagnosis. That pattern matches what the Animal Health Trust found more than a decade earlier. A sore back is frequently one part of a larger problem, and a horse treated only at the spine is often a horse treated incompletely.

The researchers behind the survey are now trying to measure rehabilitation properly. Tracy Bye, a senior lecturer in equine science at the Royal Agricultural University, is the principal investigator on an international study, with Brassington leading the work, that follows horses diagnosed with kissing spines or thoracic facet joint arthritis within the previous two months, with an initial owner survey followed by further surveys at three and six months after diagnosis.

What Buyers and Owners Should Do

The position here is straightforward. A buyer should never walk away from a horse on the strength of back radiographs alone, and an owner should never book surgery on the same basis. When a vetting turns up narrowed spaces, the useful question is whether the horse shows back pain on examination and under saddle, and whether that pain changes when the area is blocked. When a horse with a confirmed sore back is headed for treatment, the hocks, the sacroiliac region and the small joints of the spine deserve the same scrutiny as the spinous processes, and the rehabilitation program deserves as much planning as the procedure.

The profession owes riders more as well. A condition this common, treated this often and argued over this widely should have an agreed radiographic grading system and a randomized trial comparing surgery, medication and structured rehabilitation in ridden sport horses. Until both exist, the shadow on the film is a reason to examine the horse more closely and nothing more.