Kissing spines 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 spines 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 spines is impingement (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 signs of discomfort. This is certainly a challenging condition with more to it that might at first appear.
Typical signs of kissing spines
The signs of kissing spines 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 spines 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 spines 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 indications of kissing spines 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 spines
A vet called to a suspected kissing spines 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. Researchers have also found evidence that the condition can be hereditary, and have identified a gene3 linked to cases of kissing spines – and its severity.
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. 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 spines 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 spines can be successfully managed with ongoing physiotherapy and targeted training to strengthen and maintain the horse’s core muscles and the muscles over the horses back to help support the spinal column. This work may need to be combined with regular, such as twice-yearly, steroid injections into the area between the relevant spinal processes to reduce inflammation.
A rehab programme of physiotherapy and training to strengthen the horse’s back and core muscles will also be required after surgery, and then maintained in the long-term to reduce the likelihood of the problem reoccuring.
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 spines 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 spines require euthanasia, unless they have other underlying issues that cause ongoing pain.
It is worth noting that some horses with kissing spines will also have limb lameness and/or suffer from gastric ulcers that may be directly or indirectly associated with their back pain. In some cases lameness only becomes clear once the back pain has been resolved. It is also possible that the back pain is secondary to the lameness, so it is always best to consider the bigger picture.
Kissing spines case study (the author’s horse)
In early 2021, my rising six-year-old 16.2hh Irish Sport Horse was diagnosed with kissing spines. He initially presented with some straightness issues, preferring to carry his left hind on an inside track on the left rein, and step out of line to the outside on the right rein. He would occasionally catch a toe behind and would often take a shorter stride with the left hind. He also struggled to maintain an outline, particularly in trot, and felt like he was pulling himself along with his shoulders, rather than pushing from behind. He would often trip in front. In general, his behaviour was becoming increasingly unpredictable and volatile, particularly when being ridden.
A lameness work-up didn’t show anything significant, but my vet agreed that he was clearly more uncomfortable when ridden than being lunged or trotted-up in hand on any surface. He went to a referral centre for X-rays and a bone scan in the hope this would help us get to the bottom of the problem. The bone scan did show up hot spots in his back and the X-rays confirmed that the bones were very close in a number of places, showing signs of occasional impingement. While at the referral centre, the vets put some pain relief into the problems areas to see if this made him more comfortable under saddle and it did seem to help.
Initially we attempted conservative treatment, with steroids into the close areas and a programme of lunging and long lining before getting back in the saddle. We saw some improvement, but in just a few weeks, it was clear he was becoming uncomfortable again. We tried an additional batch of steroid injections into his back to help him through this tricky period, then a few weeks later, we had an incident while being ridden that resulted in me needing an ambulance ride to A&E. At this point we decided to go for surgery. We turned him away for the month or so we had to wait for his appointment as he was being increasingly difficult to handle at this stage.
My horse had an ISLD in four places under standing sedation, combined with a bone shave (ostectomy) of one process, in mid June. He was discharged a few days after surgery and moved to a specialist rehab yard, where he stayed until the end of August. They oversaw his two weeks of box rest, after which his staples were removed, then gradually reintroduced controlled exercise, including use of a water treadmill every other day, along with lunging, long-lining and turnout, enabling him to build up his strength gradually. He also had physio sessions. His general demeanor improved considerable, making him much easier to handle. I had his saddle refitted in mid August and sat back on him for the first time late August, before bringing him home to his normal yard.
Over the next few months we did a lot of groundwork, long-lining and lunging, including work over poles, with small amounts of ridden work, which we increased gradually. We started hacking out in mid September and had our first canter under saddle in November. He continued to show improvement in his strength and way of going, until I felt he was ready to have his first small jumps under saddle in February – eight months after surgery.
We are now almost a year on from there and he is in full regular work and feeling well. I continue to monitor his back carefully with physio every eight weeks and frequent saddle fit checks. I also work to maintain his core strength, including daily carrot stretches, two days a week working in-hand, and ridden polework every week. He is working on the flat and jumping better than ever and I feel very positive about his future.
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 January 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
3. Genomic loci associated with performance limiting equine overriding spinous processes (kissing spines) L.Patterson Rosaa, B.Whitaker, K.Allen, D.Peters, B.Buchanan, S.McClure, C.Honnas, C.Buchanan, K.Martin, E.Lundquist, M.Vierra, G.Foster, S.A.Brooks, C.Lafayette – 5 December 2022
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