Dorsal Spinous Process Impingement
Also known as:
Dorsal spinous process impingement or overriding dorsal spinous process, is often referred to as “kissing spines” and has been reported as the most common cause of back pain in the horse.
The dorsal spinous processes, the sections of long, thin bones which project upwards from the horse's vertebral column, are interconnected by ligaments called interspinous ligaments. In the back of a normal horse, these processes are evenly spaced apart from one another. However, if the space between the spinous processes is reduced and they get too close together, this causes them to impinge on one another.
Typically horses have about a five millimeter (just over 3/16th inch) space between those bones; however, in Kissing Spines cases, that space is narrowed until those bones are close together, touching or overriding.
These bony prominences involved in the condition start at the horse’s withers with the first thoracic vertebra (T1) and continue to the point of the hip with the last lumbar vertebra (L6), with T13 – T18 being the most commonly affected. In fact, most Kissing Spines are seen between T14 - T15 and T15 - T16, where the slant of the spinous processes change direction from a slight angle backward to a slight angle forward. This is also directly underneath where the rider sits.
Bony prominences involved in the kissing spines start at the horse's withers with the first thoracic vertebra (T1) and continue to the point of the hip with the last lumbar vertebra (L6), with T13 - T18 being the most commonly affected.
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The condition may be dynamic, where impingement only occurs when the horse is moving, or static, where impingement occurs even while their at rest and may even become fused. It is this impingement which is what causes the horse pain, which can range from mild to severe.
Kissing spines most frequently affects the horse's thoracic vertebrae, which consists of the area from the withers to just behind where the saddle would sit.
Not every horse with spinous process impingement on X-ray shows acute back pain. Second, there is no one clinical sign that clearly points to Kissing Spines as the cause.
- Has back stiffness or is hollow and inverted
- Demonstrates a resistance to work such as refusing jumps or being “behind the leg”
- Bucks, rears,, bolts, kicks out, tosses the head, shies
- Makes it difficult to mount
- “Scoots” forward as soon as mounted
- Changes from normal temperament, demeanor, and even facial expression while working or being prepared to work
- Unwilling to go “on the bit” or execute smooth transitions
- Struggles to pick up or maintain the canter, the correct lead, or a proper three-beat gait; cross-canters, has a disunited canter, or breaks from the canter
- Has loss of muscle mass across the topline
- Reluctant to roll or lie down
The underlying cause of the condition, and whether genetics plays a role, is still largely undetermined. In some cases, problems develop after a fall or other injury, but more often it is the conformation of the horse, a short back or the vertebrae themselves having narrow interspinal spaces, that is involved. kissing spines may occur in any horse but seem more prevalent in Thoroughbreds, horses 5 years of age and under, and dressage horses. However, it also frequently seen in warmbloods and quarter horses, as well as horses that jump, including hunters, jumpers, and event horses.
While some horses may be genetically predisposed to kissing spines and present clinical signs on an x-ray as early as 2-years-old, there are a great number of factors that go into determining if that horse will ever develop the condition, including the horse's level of training and the specific discipline. Horses performing a sport that requires a high amount of flexing and bending of the back will oftentimes have increased odds of developing clinical symptoms of kissing spines in comparison to low-impact or more leisure-based sports — consider a cutting horse versus a trail horse.
Kissing spine problems have been blamed on the weight of a rider, especially in young horses or those that are not in good physical condition. However, researchers studying the skeletons of long-extinct horses have found evidence of kissing spines in these animals, so while weight-carrying does reposition the shape of the spine to some extent, not all problems with kissing spines are related to the presence of a rider.
One researcher found that the highest prevalence of cases of ORDSP, or “kissing spines,” in the horses he studied occurred in competitive jumping horses.
The demands of dressage including the engagement of the hind end, periods of sitting trot by the rider, and so on, may allow pain from kissing spines to be noticed more readily than in some other disciplines, but it has not been shown that the movements necessary in dressage actually contribute to the development of kissing spines.
Currently, researchers are working to apply the latest biomechanical research in ways that redefine traditional approaches to equine training to see if changes to ways horses are trained and engage in exercises will help prevent kissing spines. According to one researcher kissing spines develop from an incorrect combination of lateral bending and transversal rotation making it necessary to create new and adequate locomotor patterns, which can only be done with the horse in motion.
Tracy Turner, DVM, DACVS, DACVSMR, of Anoka Equine Veterinary Services in Elk River, Minnesota, believes that horses are not born with kissing spines. “I have radiographed the backs in a significant number of neonates and have not found evidence of ODSP.... Consequently, predisposing conformation coupled with specific use and inappropriate riding technique may be the contributing factors to development of the condition.
In short, more research needs to be done to determine how to prevent dorsal spinous process impingement.
Treatment of kissing spines starts with making the horse more comfortable, followed by a program of physical therapy to strengthen back and abdominal muscles, stabilize the posture, and improve mobility. Relieving the pain associated with Kissing Spines can be approached medically or surgically. Changing or refitting saddles is helpful for many horses.
Every case is different and some horses will respond better to one type of therapy than another. If the horse does not improve with medical therapy or the condition recurs quickly, then surgical therapy may be recommended.
Treatment can help the majority of horses to be more comfortable, relieving at least some of the pain and stiffness in many cases. Horses that respond well may be able to return to their original level of performance, though not all affected horses have this outcome.
Unless the kissing spines is very advanced, most veterinarians will likely recommend starting with a conservative, medical approach to the treatment of this condition. Methods to control the pain and inflammation and therefore break the muscle spasm cycle and restore motion include:
- Injecting corticosteroids directly into the interspinal spaces
- Mesotherapy, a pain-dampening technique of injections that stimulate the mesoderm, the middle layer of the skin)
- Shock wave therapy
- Therapeutic ultrasound
- Non-steroidal anti-inflammatory drugs (NSAIDs)
- Muscle relaxants
When a medical approach is insufficient, two different surgical procedures are usually available. The veterinary team made up of the referring vet and the surgeon will recommend the one that is most suitable for the horse and situation.
In one procedure, parts of the bony spinous processes themselves are actually removed. While this can be done under general anesthesia or standing sedation and a local nerve block, it is considered the more invasive and costly of the two procedures and requires a longer recovery and rehabilitation time.
The second procedure is known as Interspinous Ligament Desmotomy or ISLD which can be performed while the horse is standing and involves cutting the ligaments that connect the affected spinous processes. It is generally less invasive, less costly, and some horses return to work in as little as six weeks.
Regardless of which surgical procedure was performed – or whether medical therapy was elected – all horses treated for Kissing Spine will need physical therapy for long-term improvement.
The specific rehab program for an individual horse will depend on the medical or surgical procedures performed, but most begin with a period of hand walking, following by lunging (usually with a “postural aid device” such as the Pessoa Lunging System or Equiband System), then a gradual re-introduction to an experience and balanced rider.