Kissing spine can cause severe pain and seriously affect a horse’s performance. Find out what the signs are and how it can be treated...
A horse with kissing spine is thought to feel consistent, low-grade pain from its back because the spinous processes (the sections of bone that point upward from the main vertebrae that carry the spinal column) press against or rub on each other during movement. The veterinary description of kissing spine is impingment (when the bones are touching) or overriding (when the bones overlap) dorsal spinous processes (IDSP/ODSP).
The bones with the spinous processes run from the first thoracic vertebra (T1) at the horse’s withers to the last lumbar vertebra (L6) at the point of the hip, with the T13 to T18 bones being the most commonly affected. This is the area where the saddle and the rider are located.
It is important to be aware that although changes on X-rays can be readily identified, they are typically insufficient to make a diagnosis. Many horses with changes on X-ray do not show any discomfort. This is certainly a challenging condition with more to it that might at first appear.
Typical signs of kissing spine
The signs of kissing spine can be subtle and are non-specific, but may include:
- The horse showing signs of discomfort (such as shifting weight, pulling faces, biting) when being groomed over the back or when pressure is applied to the back such as when the saddle is put on or girthed up
- Changes to the horse’s normal temperament and demeanour when working or being prepared to work
- The horse may become difficult to mount, refusing to stand still, running backwards or forwards when the rider’s weight is added
- When being worked the horse may show signs of stiffness through the back. It may be unwilling/unable to work ‘on the bit’ preferring a hollow or constantly changing outline or repeatedly tossing its head.
- The horse may struggle to make transitions between the paces or within a pace, dropping behind the rider’s leg and show a reluctance to go forwards with impulsion
- The horse may buck, rear, run away, kick out, or repeatedly shy
- Canter is often a key indicator of kissing spine with many horses struggling to pick up the correct lead or maintain a true three-beat canter, tending to break or go disunited instead
- A horse with kissing spine is likely to show a loss of muscle mass across its topline
- Horses may also be reluctant to roll or lie down
Many of the typical signs can also be caused by a behavioural or training issue, or a medical condition that is not related to the horse’s back, so keeping a note of any changes you notice so you can share this detailed history with a vet is key so they can form part of the discussion prior to diagnosis.
It is noteworthy that some horses live with signs of kissing spine shown on X-rays without showing signs of discomfort and enjoy a successful working life without requiring any veterinary intervention.
If your horse is showing a combination of the signs above, we would recommend working with your vet and your trainer together to identify the source of the issue as soon as possible. Further investigations are important rather than relying on vague signs or X-rays alone.
Diagnosing kissing spine
A vet called to a suspected kissing spine case will want to hear the horse’s history and will take into consideration its age, breed and gender. They will typically undertake a complete physical examination of the horse, including hands-on palpation of the entire body – not just the horse’s back.
This will be followed by a lameness examination, with the horse trotted-up in hand, potentially lunged and then worked under saddle, if this can be done safely, so they can compare the horse’s movement and way of going with and without a load on its back.
Some vets will inject a local anaesthetic between the spinal processes that they believe to be troublesome — basically a nerve block — before repeating the lameness work-up. Ultimately thorough clinical imaging is the best way to confirm if the spinal processes are impinging on each other. As well as the often all too obvious X-ray changes, nuclear scintigraphy (bone scans), thermography, and ultrasound are also options that can provide helpful information.
“Kissing spine often has very subtle symptoms,” says Dr Svend Kold, a specialist in equine orthopaedic surgery. “We watch the horse being schooled and look at everything, including the horse’s demeanour, limbs, posture, whether he is accepting the bit, whether he unlocked in his back, and the expression on his face. The trot is often okay, but the horse invariably struggles to maintain a three-beat canter and frequently gets disunited.”
What types of horses are affected?
It is predominantly racehorses and competition horses who are referred for treatment. This could be because it is more noticeable in performance horses due to the physical demands on them, while in horses just used for hacking and low-level work, the problem may go unnoticed. Alternatively, it may be that performance horses are more prone to the condition, due to the physical demands placed on them. There is also a belief the condition may be hereditary.
Veterinary literature has suggested that up to 34% of horses (which tend to be over-represented by thoroughbreds) may show signs of kissing spine on X-rays, but many do not exhibit any clinical signs as a result of them and may not have any disease. It is always important to rule out other causes for concern, such as a poorly fitting saddle, rider issues or indeed lack of fitness.
Treatment for kissing spine
In cases where a definitive diagnosis has been made that the kissing spine are the true site of pain with the horse showing obvious signs of discomfort, surgery can be used to rectify the problem. However, the original operation developed has been modified in recent years to offer a far less invasive, and much cheaper option, with a far shorter recovery period.
“Instead of removing sections of bone, the ligaments between the spinal processes are cut — an Interspinous Ligament Desmotomy (ISLD),” explains Ricky Farr, MRCVS. “This can be done under standing sedation.
“Some of the ligaments between the spinous processes in the back are cut through a very small incision (usually less than 1-2 cm) in the skin. This technique has gained popularity among surgeons due to being minimally-invasive and horses are often back into work within six to eight weeks.”
The ISLD is typically best suited to cases were the spinous processes are close and believed to be touching at times when the horse is in motion, rather than cases where the bones are significantly overlapping. In these cases, removal of bone may be required.
The original operation, which was developed in the 1980s, saw significant chunks of bone removed from the spine under general anaesthetic with recovery times of three months or more. The risk of complications from this type of surgery is also much higher.
In some cases an ISLD under standing sedation is now combined with a ‘bone shave’ process, where some smaller sections of bone are removed via an incision along the top of the back, but which does not require a general anaesthetic.
Dr Kold explains the traditional surgery process: “After the incision along the back, we would cut through the supraspinous ligament. Once all muscular and ligamentous attachments are severed down either side, we cut off around half the spinal processes, removing about three inches of bone. Next, the ligaments and skin are sutured. After the procedure, a void is left, as the bone doesn’t re-grow and a blood clot forms, followed by fibrous tissue.”
A small US study1 (18 horses), published in 2020, found horses which showed improvement when having their back ‘blocked’ with local anaesthetic during diagnosis were more likely to experience a long-term improvement in clinical signs after undergoing ISLD surgery than those who did not tested prior to surgery.
Non-surgical treatment options
Whether or not to operate depends on how badly the bones are pressing on each other, the individual horse’s tolerance levels, his lifestyle and the owner’s financial situation.
Some horses with confirmed kissing spine can be successfully managed with a regular, such as twice-yearly steroid injection into the area between the spinal processes. This will need to be combined with ongoing suitable physiotherapy and training to strengthen and maintain the horse’s core muscles and the muscles over the horses back to help support the spinal column. A rehab programme of physiotherapy and training to strengthen the back and core muscles will also be required after surgery.
Equine surgeon Bruce Bladon says: “In cases where we’re talking about the normal flexibility of the spine occasionally resulting in the edges of the bones ‘kissing’, it is easy to see how increased muscle tone as a result of physiotherapy and a change in work, might prevent this.”
Other methods that your vet may recommend to help control the pain and inflammation associated with kissing spines include:
- shock wave therapy
- therapeutic ultrasound
- non-steroidal anti-inflammatory drugs (NSAIDs)
- muscle relaxants
Most horses diagnosed with kissing spine are able to return to ridden work after appropriate veterinary treatment and a recommended rehab programme is completed. In some cases they may be unable to return to the same level of work as before, but are comfortable when working at a lower level. Research from a 2019 study2 of 71 cases dating from 2012 to 2017 undertaken in the US found 91.1% of horses successfully returned to work after ISLD surgery, with 52.9% returning to the same or a higher level of performance than before surgery.
Paddock retirement is an option for most horses if the owner is unwilling or unable to undertake the appropriate veterinary treatment and rehabilitation that the horse requires, but some will cope well with an adjusted riding regime, so never give up too quickly. Very few horses with kissing spine require euthanasia, unless they have other underlying issues that cause ongoing pain.
It is worth noting that some horses with kissing spine will also have limb lameness that may be directly or indirectly associated with their back pain. In some cases this lameness only becomes clear once the kissing spine has been resolved. It is possible that the back pain is secondary to the lameness, so always best to consider the bigger picture.
1. Long-term outcome and effect of diagnostic analgesia in horses undergoing interspinous ligament desmotomy for overriding dorsal spinous processes Kara A Brown, Elizabeth J Davidson, Kyla Ortved, Michael W Ross, Darko Stefanovski, Kathryn B Wulster, David G Levine – 9 Jan 2020
2. Long-term prognosis for return to athletic function after interspinous ligament desmotomy for treatment of impinging and overriding dorsal spinous processes in horses: 71 cases (2012-2017) Amanda J Prisk, José M García-López – 22 July 2019
A controlled study evaluating a novel surgical treatment for kissing spines in standing sedated horses Richard P C Coomer, Shaun A McKane, Naomi Smith, Jean-Michel E Vandeweerd – 25 June 2012
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