Overriding Spinous Process, otherwise known as Kissing Spine, can cause back pain and poor performance, especially when two or more vertebrae touch or overlap. Assistant Professor Dr. Nathalie Cote in the department of Large Animal Surgery at Ontario Veterinary College recently presented a new less invasive surgical approach to treat this issue that is showing great preliminary results.
While there is very little movement in the lumbar area of a horse’s spine, the thoracic area just in front of it has a slightly wider range. Thoracic vertebrae allow side-to-side flexion, a little rotation and flexion and extension which allow the back to move up and down. Impingement most frequently occurs under the saddle area between thoracic vertebrae T13 to T18 with T14 to 16 (right where the rider sits) being the most common.
Not all riding horses with kissing spine will present with clinical signs. In fact, it is not uncommon to find Kissing Spine post-mortem in riding horses that have not shown obvious signs of pain. Kissing Spine has also been found in post-mortems of extinct and undomesticated horses which leads to conclusions that in some cases conformation plays a role.
In horses with spinal impingement that do present with back pain and behavioural signs (bucking, rearing, refusing jumps, being girthy or sensitive to brush, etc.), there are typically more than one vertebrae affected and the severity of impingement is greater. A grading system of one to four is assigned when diagnostic radiographs are performed. In grade one, there is narrowing of the space between the spinous process; in grade two, that loss of space is significant; in grade three, bone remodelling has begun; and in grade four, malformation will be significant and the space is almost impossible to go in between in past surgical options.
Cote explains, desmotomy (ligaments are severed and potentially redistributed) with a scissor tool proves challenging when it comes to grade four cases and treatments involving partial removal are costly and invasive.
The modified procedure of surgical desmotomy of the interspinous ligament uses a tool much smaller than scissors allowing a smaller incision to be made and resulting in improved cosmetic appearance. The modified procedure makes it easier to work with the minimal spaces seen in grade four cases. It is a quicker, less invasive procedure which begins with inserting needles into the interspinous spaces. X-rays are then taken and the needles are removed for the areas that will not be operated on and left in for those that will be worked on. A one-centimetre incision is made using a narrow tenotome tool to dissect the identified ligaments which restores space between the thoracic vertebrae.
So far, clients adhering to a six-week rehabilitation program of stall rest and hand-walking (three weeks) followed by lunging, core strengthening and mobilizing exercises generally receive a very good prognosis for the scar tissue to heal well and mobility to be restored. Some clients reported going back into full training as early as four months after the surgery.
Dr. Nathalie Cote presented modified procedure of surgical desmotomy of the interspinous ligament findings to a group of Ontario Association of Equine Practitioners (OAEP) on Feb 15, 2023 at the University of Guelph. The presentation is available below.
(Equine Guelph; Generic photo of horse in field not diagnosed with Kissing Spine)