Kissing spine in horses shows up as bony projections along the top of the spine that have moved too close together, touching or even overlapping instead of maintaining healthy spacing. On X-rays, a normal gap between these projections (called spinous processes) measures at least 4 millimeters. When that gap narrows below 4 mm, or disappears entirely, the horse has what veterinarians formally call overriding dorsal spinous processes. The name “kissing spine” comes from the way adjacent bones appear to “kiss” on imaging.
What It Looks Like on X-Rays
Radiographs are the primary way kissing spine is identified, and the condition follows a grading scale from mild to severe. At Grade 1, the interspinous spaces are simply narrower than normal. You can still see daylight between the bones, but the gap is tighter than it should be. Grade 2 shows the edges of the spinous processes becoming denser and more opaque on the film, a sign that the bone margins are thickening in response to repeated contact.
Grade 3 is where things start looking more alarming. The X-ray reveals areas of bone loss (lysis) along the margins where the processes meet, appearing as dark, irregular patches eating into the bone edges. By Grade 4, the spinous processes have undergone severe remodeling. Their shapes are distorted, with irregular contours, new bone growth, and sometimes complete fusion. At this stage, the original smooth, evenly spaced profile of the spine is replaced by a crowded, jagged silhouette.
The condition most commonly affects the mid-back region, roughly where the saddle sits. The thoracic vertebrae in this area have the tallest spinous processes, which makes them more prone to crowding and contact.
What It Looks Like on the Horse
From the outside, kissing spine doesn’t always produce visible changes, especially in early stages. But as the condition progresses and causes pain, you may notice a combination of physical and behavioral signs that paint a recognizable picture.
Muscle atrophy along the topline is one of the more visible clues. A horse with back pain often stops engaging the muscles along its spine, and over weeks or months those muscles visibly shrink. The spine may appear more prominent, with a “peaked” or bony look along the back rather than the smooth, rounded muscling of a healthy topline. Some horses develop a dipped or hollow back posture, carrying themselves with their head up and their back dropped away from the rider.
Girthiness is another hallmark. When you tighten the girth or cinch, the horse may pin its ears, swing its head around to bite, or flinch and shift away. Sensitivity to grooming or pressure along the back is common too. Running your hand firmly along either side of the spine might cause the horse to dip sharply, flinch, or tense visibly. In more severe cases, horses resist saddling altogether or become difficult to mount.
What It Looks Like Under Saddle
Ridden behavior often changes before anything is visible on the horse’s body. A horse with kissing spine may resist collection, refuse to round its back, or become stiff and unwilling to bend. Bucking, especially during transitions or when asked to canter, is a classic behavioral sign. Some horses simply feel “off” without showing obvious lameness, performing below their usual level with a shortened stride or reluctance to move forward.
Cross-cantering, difficulty with lead changes, and resistance to lateral work can all point to back pain from impinging spinous processes. These signs are easy to mistake for training issues or attitude problems, which is one reason kissing spine sometimes goes undiagnosed for months.
What Ultrasound and Bone Scans Add
X-rays show the bone changes, but they don’t tell you whether those changes are actively causing pain right now. That’s where additional imaging comes in. A bone scan (nuclear scintigraphy) highlights areas of active inflammation or bone remodeling as bright “hot spots.” If the spinous processes light up on a bone scan, it suggests the area is currently inflamed and likely painful, not just an old finding.
Ultrasound offers a different view. It can reveal changes in the soft tissue between and around the spinous processes, particularly the ligament that runs along the top of the spine. On ultrasound, this ligament normally appears as a smooth band that changes in brightness as it passes over each vertebra. When kissing spine is present, the ligament may look thickened, irregular, or show signs of mineralization (bright, dense spots within the tissue). The spaces between the processes may appear compressed or filled with abnormal tissue rather than showing the normal, clean gap.
Radiographic Signs Without Symptoms
One important nuance: X-ray findings alone don’t confirm a diagnosis. Some horses show narrowed or even touching spinous processes on radiographs but perform perfectly well with no signs of discomfort. This means that what kissing spine “looks like” on film doesn’t always match what it looks like in real life. The diagnosis depends on connecting imaging findings with clinical signs, often using local anesthetic injections between the spinous processes to confirm the area as the pain source.
What Recovery Looks Like After Treatment
Treatment ranges from conservative management (rest, targeted exercises, corticosteroid injections between the affected processes) to surgery. Surgical options include cutting the ligament between the spinous processes to relieve tension or removing portions of the bone itself to recreate space. Studies show that 72 to 91 percent of horses that undergo surgery return to some level of performance, though the timeline varies. A survey of equine veterinarians found that among those who followed horses after surgery, about a third reported that fewer than half showed immediate improvement in clinical signs. Recovery is often gradual, with rehabilitation exercises playing a major role in rebuilding the topline muscles that support the spine long-term.
After successful treatment, the visible signs reverse over time. The topline fills back in, the horse moves more freely, and the reactivity to grooming and saddling fades. On follow-up X-rays, surgically treated spaces appear wider, and the bone margins may smooth out as inflammation resolves.