Kissing Spines in Horses

How veterinarians diagnose and rehabilitate horses suffering from kissing spines

Kissing spines is a deceptively sweet nickname for a painful back problem. It occurs when the top “shark fin” or dorsal spinous processes (DSPs) of the thoracic vertebrae—about where the saddle goes—crowd, touch, or overlap one another.

As you might imagine, an equine athlete with an abnormal spinal column can experience quite a bit of discomfort, particularly when ridden. Depending on the individual horse and the severity of the condition, pain manifests in a variety of ways. From mild performance issues and slight discomfort on palpation to massive behavior issues—bucking and refusing to move forward as directed—kissing spines can be surprisingly challenging to recognize. It can also mimic many other causes of back pain (TheHorse.com/185297).

Here’s what you need to know about this condition and what to do when your horse’s vertebrae decide to steal a kiss.

Understanding the Issue

Each vertebra in the thoracic spine has a process projecting upward along its top (or dorsal) aspect. These processes are quite tall in the thoracic region, though heights vary by anatomic location and horse breed. In a perfect world the DSPs align in a neat row along the length of the spinal column without tilting. There should also be an appreciable space between each of the processes’ tips.

In some horses the space between adjacent DSPs narrows over time. When the processes simply approach one another or gently touch, we refer to the condition as impinging DSPs. When they overlap, we refer to them as overriding (ODSPs). In this article kissing spines refers to all types.

The condition primarily affects the 13th to 18th thoracic vertebrae, as well as the first and second lumbar vertebrae. These vertebrae are located about halfway along the top of the rib cage to the middle of the back, where the thoracolumbar junction lies.

“Poor conformation and conditioning, rider-horse mismatch, poor training, and chronic use of an ill-fitting saddle appear to be the predominant predisposing factors associated with overriding DSPs,” says José García-López VMD, Dipl. ACVS, ACVSMR, associate professor of large animal surgery and director of equine sports medicine at Tufts University’s Cummings School of Veterinary Medicine, in North Grafton, Massachusetts. “When the horse is exercising, the ­thoracolumbar spine will dorsi- and ventroflex (bend up and down). If the supporting muscles around the spine, in particular the multifidus and spinalis muscles, are not properly developed or (are) improperly conditioned, then more load and stress is placed upon … bony structures in the back. Over time, changes in the conformation of the back might occur.”

Diagnosing Kissing Spines

If a physical examination points to back pain in the thoracic spine area, radiographs (X rays) will help the veterinarian determine if those spines are kissing. 

“These images provide detailed information regarding the orientation of the dorsal processes, whether they are or are not touching, fused, or overriding, and if there are other changes characteristic of bony inflammation and remodeling,” says García-López.

Regardless of the X ray findings, owners of horses with back pain should expect their veterinarians to conduct X rays and at least one other advanced diagnostic imaging technique.

“X rays alone do not provide sufficient information to determine whether or not ODSP is actually the cause of back pain,” says García-López. “Even horses with ODSP visible on radiographs can actually be clinically normal, with no pain isolated to the back on physical examination. In these cases the ODSP is simply an incidental finding.”

Indeed, about 87% of study horses in one report (Zimmerman, 2015) had radiographic changes consistent with kissing spines, but not all of them had back problems. 

To complicate matters further, because of the condition’s dynamic nature, radiographs taken when a horse is at rest might not reflect what’s happening when the horse works. Those spines could touch or overlap only once a horse gets moving.

García-López says nuclear scintigraphy (bone scan) is a critical imaging tool that many vets deem invaluable when used in conjunction with the physical exam, diagnostic analgesia, and radiographs. It involves injecting a radioactive-laden tracer into a horse’s vein and using a gamma camera to identify where it localizes in the body. Bone with active turnover (metabolism), such as due to injury, will take up the radioisotope more than ­surrounding tissue, showing as “hot spots.”

A positive relationship exists between severity of radiographic findings and intensity of radiopharmaceutical uptake during a bone scan: A higher radiographic grade of kissing spines paired with intense radiation on bone scan supports a DSP diagnosis (Zimmerman, 2015).

Thinking of skipping right to the bone scan? Think again. Just like X rays don’t necessarily correlate with clinical signs, positive scintigraphic findings alone are not always associated with primary bone injury. A supraspinous ligament injury, for example, can also cause uptake in the summits of the DSPs.

Only after appropriate imaging confirms DSPs can the veterinarian consider the many treatment options.

The Therapeutic Toolkit

For best results vets usually pursue a multimodal treatment approach for ODSP, often involving a combination of:

  • Systemic anti-inflammatory drugs (e.g., oral phenylbutazone or “Bute”);
  • Anti-inflammatory corticosteroids, such as methylprednisolone acetate or triamcinolone, injected directly into the interspinous spaces;
  • Physiotherapy;
  • Extracorporeal shock wave therapy (ESWT);
  • Mesotherapy;
  • Off-label bisphosphonates (drugs designed to inhibit bone resorption and labeled to treat navicular pain);
  • Exercise and training implements; and
  • Surgery.

Veterinarians aim to reduce inflammation with these therapies in the areas where the spinous processes either touch or overlap. In turn, inflammation associated with bony remodeling and concurrent soft-tissue damage also diminishes.

Let’s take a closer look at three popular nonsurgical options:

ESWT

Many veterinarians use this modality to treat horses suffering from back pain but, as García-López points out, no objective data exist for it as a treatment for kissing spines.

Andrew Fiske-Jackson, BVSc, MVetMed, FHEA, Dipl. ECVS, MRCVS, is senior lecturer in equine surgery and deputy head of the Royal Veterinary College’s Equine Referral Hospital, in Hertfordshire, U.K. “This technique demands accurate placement of the probes because they only have a small focal area of pulses,” he says. “I recommend using 35-millimeter probes for kissing spines. One thousand pulses are delivered to each side, then horses are rested for two days and returned to work over five days. I would use this treatment for competition horses requiring swift pain relief without the longer withdrawal period required following drug therapies.”

Typically, veterinarians must repeat ESWT approximately every six to 12 months to maintain the horse’s comfort.

Injectables

Medicating the interspinous space between dorsal processes is one of the most common medical modalities. Veterinarians typically use a combination of an anti-inflammatory (e.g., Depo-Medrol) and one or more analgesics (pain relievers), such as Carbocaine or Sarapin. They might also use these medications for mesotherapy, which involves injecting pharmaceuticals into the middle layer of the skin—the mesoderm—on either side of the spine to block pain (nerve) fibers.

Implements

Training and rehabilitation aids such as longeing and band systems can help encourage an affected horse to lower his head and engage his hind limbs, Fiske-Jackson says.

“Rehabilitation should focus on flexing the spine,” he explains.

Actions that flex the spine include forelimb retraction and hind-limb protraction —when the front legs extend backward and the hind limbs move forward. Lowering the head also flexes (arches) the spine by tensing the nuchal ligament at the crest of the neck and rotating the thoracic vertebrae as if the horse were preparing to do a forward roll in gymnastics. 

When used correctly, these tools can help the back flex properly, says Fiske-Jackson. “Training aids are best used in conjunction with trotting poles and raised trotting poles to further encourage hind-limb engagement,” he adds.

Surgical Options

If problems persist despite conservative and medical treatments, vets might then turn to surgery, says Richard Payne, BSc, BVSc, CertES(Orth), Dipl. ECVS, MRCVS, a European veterinary specialist in large animal surgery at Rossdales Equine Hospital, in Newmarket, U.K.

The veterinarian’s goal when performing any DSP surgery is to relieve the ­impingement between adjacent spinous processes. Payne says one approach involves cutting the fibers of the ­interspinous ligament—the band of soft tissue that runs along the top of the spinous processes. This technique, called a desmotomy, serves two purposes:

  1. To increase the interspinous space and stop the impingement.
  2. To relieve tension on pain receptors. 

At the European College of Veterinary Surgeons’ 2014 Scientific Meeting, Payne reported that about 80% of his patients return to athletic function and 60% return to their previous level of work within 12 months of surgery.

García-López and colleague Amanda Prisk, VMD, Dipl. ACVS, report similar results. In their review of 71 horses that underwent interspinous ligament desmotomy, 91.1% returned to some level of performance and just over half reached an equivalent or higher level of performance than before surgery. They noted pain recurrence in some horses that did not return to prior levels of performance, but 82.1% of horse owners said they would recommend the procedure to others.

A desmotomy can only be performed, says Payne, if a solid “bridge” does not exist between adjacent spinous processes. If a bridge has already formed, then the surgeon might elect to perform a partial or total resection of the summit of the affected DSPs—a procedure that can be executed in a standing sedated horse.

Payne says he has seen a wide range of anatomic abnormalities when performing resections, from mild new bone formation on adjacent spinous processes to flaring (i.e., a change in the bone’s shape) and extensive bony callus formation between two or more adjacent spinous processes.

Post-Treatment Steps

Regardless of the medical or surgical approach, García-López says rehabilitation exercises throughout recovery are “critical in order to have a good­ ­outcome.”

In fact, Fiske-Jackson typically advises against simply resting a horse with back pathology, because rest can lead to muscle loss that further complicates and delays the horse’s return to work.

“Large studies of back pain in people have found that strength/resistance and coordination/stabilization exercise improves outcomes over other interventions,” he says.

In his practice Fiske-Jackson manages kissing spines medically using an eight-week program.

  • Weeks 1 and 2 10-20 minutes walking per day.
  • Weeks 3 and 4 Add five minutes of longeing with a training aid such as an Equicore Concepts Equiband or a Pessoa longeing system. Add baited carrot stretches daily.
  • Weeks 5 and 6 Add another five minutes of longeing and trotting poles.
  • Weeks 7 and 8 Add raised trot poles.

At the end of eight weeks the horse can begin ridden exercise.

“This program should be tailored and adjusted according to the athletic ability and fitness of the horse,” he says. “That said, it is intentionally robust in order to strengthen the very core stabilization muscles that we know atrophy in the presence of back pain.”

Take-Home Message

While we’ve provided a road map for diagnosing and treating back pain due to kissing spines, our sources caution owners that the process isn’t always this clear.

“Despite advances in diagnostic imaging techniques, the accurate investigation of back pain in horses remains a problem,” says Payne. 

As diagnostics evolve, he says, veterinarians hope to achieve more pointed diagnoses and specific treatment modalities. In the interim, remember that many causes of back pain can present similarly, and discomfort unrelated to the back can cause classic signs of kissing spines.