Kissing spine is a skeletal abnormality in horses in which bony projections on the vertebrae of the spine touch or “kiss”. These projections are called dorsal spinous processes.
This condition is caused by multiple factors including conformation issues, genetic predispositions, poor posture, improper conditioning, and training under saddle at a very young age.
Horses with kissing spine do not always develop symptoms, but many horses with this condition experience back pain. Afflicted horses may exhibit extreme back tightness, bucking, pain on palpation and an inability to stretch and raise the back while under saddle.
Most horse owners dread having their horse diagnosed with kissing spine. For a long time, it was thought that horses with symptomatic kissing spine could no longer be ridden and had to be retired.
However, surgical advances and modern rehabilitation techniques give new hope to owners of horses with kissing spine. There are many therapies available to keep your horse comfortable and to re-establish mobility.
Have your veterinarian examine your horse if you think they are experiencing back pain. If left untreated, horses with kissing spine can act out under saddle, putting themselves and their riders at risk.
Kissing Spine: An Emerging Concern
Kissing spine is sometimes referred to as dorsal spinous process impingement syndrome.
Kissing spine commonly affects multiple vertebrae of the thoracic spine, in particular T14- T18. This is the area around the anticlinical vertebrae or the area of the spine where the dorsal spinal process change orientation. This is also the area under the saddle and the rider. However, it can occur along the entire length of a horse’s back. 
This condition is diagnosed by a veterinarian upon radiographic detection of overriding dorsal spinous processes (ORDSP). Kissing spine diagnosis has increased significantly in recent years due to the increased use of digital radiographs (x-rays). 
Your veterinarian will perform x-rays along the spine to determine whether the vertebrae in the spine are too close or touching. When examining an x-ray of the back, veterinarians look for reductions in the space between dorsal spinous processes and changes to the boney areas.
Ultrasound imaging can also be used to assist with diagnosis. It can be combined with the information in the x-rays to give information of changes the dorsal spinous process surface, supraspinous ligament damage, multifidus muscle changes and facet joint involvement.
Your veterinarian may also suggest a bone scan (Nuclear Scintigraphy), which involves injecting your horse with a radioisotope and using a bone scan camera. The camera is positioned over your horse’s back to detect hot spots – areas where radiation is absorbed into the bone. These hot spots indicate areas of inflammation and likely pain. 
Bone scans are considered more accurate in differentiating clinical versus non-clinical cases of kissing spines. These scans are usually only conducted at referral practices.
Some veterinarians will use local anesthesia (freezing) to test if blocking the pain helps alleviate symptoms of kissing spines.
Back Pain in Horses
Kissing spine does not always cause pain in horses. In fact, some cases of kissing spine are found accidentally while investigating other issues in asymptomatic horses. In one study 39% of horses that were radiographed despite lack of back pain still had radiographic changes suggestive of kissing spines. 
However, in the same study, 68% of horses that did present for back pain were diagnosed with kissing spine. This suggests that this condition is a major contributor to equine back name.
When kissing spine does cause pain it can be quite severe. Horses with this condition can experience pain for the following reasons:
- The bony dorsal spinous processes grinding against each other
- Injury or inflammation of the ligaments between the processes
- Reduced of range of motion in affected vertebral segments, resulting in muscle tightness
- Impingement of the nerves exiting the spinal cord through the foramen of the affected vertebral segments
Causes of Kissing Spine
Although research is ongoing, scientists have determined that kissing spine is a result of multiple factors.
Research has indicated that Warmbloods, Thoroughbreds, and Quarter Horses are more likely to develop kissing spine than other breeds.
This may be a consequence of genetic factors as many horses of these breeds trace back to the same sires. It may also be because these breeds tend to be ridden at younger ages, prior to reaching skeletal maturity. 
Horses with shorter than average backs are more likely to develop kissing spine. These horses have the same number of vertebrae in a smaller area, resulting in decreased space between the vertebrae. 
Researchers have identified a strong genetic link to kissing spine. Recent research has identified specific chromosomes that increase the risk of kissing spines 
Unpublished data from Etalon Diagnostics indicates that horses born from parents with kissing spine are more likely to develop the condition later in life.  Continued research can help with the selection of mares and stallions to prevent the genetic predisposition to kissing spine.
Horses that are ridden with a high head and hollow back or trained under saddle too young are more likely to develop kissing spine. 
If the horse’s topline and back are weak and unable to carry a rider properly, the dorsal spinous processes are not able to lift and spread.
This can continue until the bones rub together or fuse, resulting in extreme pain. 
Negative Plantar Angle of the Hind Feet
Negative plantar angle refers to a collapsing of the heels or tipping up of the coffin bone. The toe of the coffin bone is slightly higher than the heel, resulting in uneven pressure on the hoof wall and sole.
When the coffin bone rotates upward in the hind feet, the horse must move its hind limbs in a way that stiffens the back in a hollow posture.  Consistent movement in this posture will bring the dorsal spinous processes closer together, resulting in kissing spine. 
Horses with kissing spine often have hock and sacro-iliac arthritis . When horses move incorrectly in their back, they will often move incorrectly in their hind end as well. Conversely, back pain can also cause hock and sacro-iliac pain as well.
Horses diagnosed with kissing spine should also have sacro-iliac ultrasound and hock x-rays to determine if treatment for arthritis in these areas is warranted. Alternative therapies, such as chiropractic and acupuncture treatments, can help with compensatory pain and improve mobility as well.
Signs & Symptoms
Although kissing spine is not always symptomatic, horses who do experience pain can display a wide variety of signs such as:
- Bucking under saddle
- Reluctance to stretch the neck and round the back
- Hind end lameness
- Discomfort when saddling or doing up the girth
- Weight loss
- Cross cantering or difficulty maintaining a canter
- Pain when palpating or brushing the back
- General irritability when moving
Because these symptoms are also associated with other conditions, it is important to discuss diagnosis with your veterinarian to rule out other health problems including:
In the past, a diagnosis of kissing spine would be a career-ender for performance horses.
Fortunately, there have been significant improvements in surgical, pharmaceutical, and rehabilitative interventions that give hope to many kissing spine horse owners.
The prognosis for horses with this condition is much better today. The majority of horses with kissing spine can return to work after following a veterinarian-recommended treatment plan. 
Treatments in use today include surgery, joint injections and non-invasive rehabilitation.
Interspinous Ligament Desmotomy
Pioneered by Dr. Richard Coomer in 2009, the interspinous ligament desmotomy (ISLD) is colloquially referred to as the ligament snip.
This procedure aims to cut the ligament between the spinous processes of the affected vertebrae, removing the source of pain and re-establishing mobility. 
While your horse is under standing sedation and local analgesia, the surgeon will make small incisions above the areas of kissing spine. The surgeon uses a very small chisel to divide the interspinous ligament in half.
Following ISLD, your horse will be on stall rest and a rehabilitation protocol as direct by your veterinarian.
This surgery comes with minimal complications and a high long-term success rate (90%). However, it does have its limitations.  Horses with greater than five lesions or extremely close spinous processes are not good candidates for ISLD.
ISLD does not cure kissing spine, but it does minimize symptoms and allow the back to move comfortably during rehabilitation.
If not rehabbed properly, some horses experience recurrence of kissing spine or develop kissing spine in other areas.
Cranial Wedge Ostectomy
The standing wedge ostectomy (or bone shave) is a much more invasive procedure, but it removes the kissing spines completely.
This surgery can be performed with your horse standing or lying on its side. The surgeon will make a large incision down the length of your horses back over the areas affected by kissing spine.
The surgeon will then cut through the supraspinous ligament, which is the large band of fibrous tissue that runs along the top of the spinous processes.
Using a bone saw, the surgeon will t