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 anticlinal 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. [14]
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 portable X-ray systems, making radiographs easy to do on the farm. [2]
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 are looking for narrowing of the space between dorsal spinous processes, as well as evidence of bony changes.
In cases of kissing spine, bony remodeling can be seen in the areas where the bones touch. Bone-on-bone contact is painful, so the body attempts to remodel the affected areas in an effort to protect itself.
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 increased metabolic activity in the bone, such as during periods of rapid bony remodeling. [1]
Bone scans are considered more accurate in differentiating clinical versus non-clinical cases of kissing spines. These scans are 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. [15]
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 pain.
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.
Predisposed Breeds
Research suggests 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. [2][3]
Conformation
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. [4]
Genetic Component
Researchers have identified a strong genetic link to kissing spine. Recent research has identified specific chromosomes that increase the risk of kissing spines [16]
Unpublished data from Etalon Diagnostics indicates that horses born from parents with kissing spine are more likely to develop the condition later in life. [5] Continued research can help with the selection of mares and stallions to prevent the genetic predisposition to kissing spine.
Improper Conditioning
Horses that are ridden with a high head and hollow back or trained under saddle too young are more likely to develop kissing spine. [4]
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 apart, leaving ample space between them.
This can continue until the bones rub together or fuse, resulting in extreme pain and limited range of motion. [6]
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. [7] Consistent movement in this posture will