Overriding dorsal spinous processes
Kissing spines is a condition that can be quite debilitating. However, a new surgical treatment option may give horses a second chance.
The horse’s spine is composed of individual vertebrae connected by ligaments and surrounded by muscles. Each vertebra has a bony prominence that extends upward from the spinal cord: the “dorsal spinous process”. This is the part of the spine that we can feel right underneath the skin along the horse's back. These spinous processes are connected to each other through the vertebrae and stabilized via ligaments that run between them and over the top of the spine. Normally, there is a gap between them so that they don’t touch each other and there’s room for the horse's movements. When a horse has Overriding Dorsal Spinous Processes (ODSP) or “kissing spines”, one or several of these gaps have become smaller. The lack of space between spinous processes reduces back mobility and can cause pain during movement as the spinous processes interfere with each other.
Kissing spines typically occurs in the last few thoracic vertebrae (in the area of T14 to T17)—right where a saddle and rider would sit along the horse’s back.
Kissing spines doesn’t always cause clinical signs and can sometimes be found on radiographs of seemingly healthy horses. Signs of reduced mobility and back pain depend on the severity of the impingement and lesions. Signs can be subtle, such as poor performance or decreased range of motion when asked to flex or extend the back. A horse with back pain may try to avoid painful situations (reluctance to be ridden or lunged, cross-cantering, bunny-hopping at canter). A horse may also display pain in response to touch (aggressive face expression, biting or kicking when being brushed, saddled or carrying a rider) or in response to movement (bucking or kicking under saddle or on the lunge).
First a vet will assess the horse's response to being handled, saddled and during movement. Your vet will palpate its back to feel for muscle tension, swellings, distance between dorsal spinous processes, pain and range of motion. Radiographs are usually taken to assess the dorsal spinous processes. Ultrasound may also be used to measure the gaps between the spinous processes and assess the ligaments that surround them, which may be injured or inflamed. Local anaesthesia may be used to block the pain in an area to confirm that the clinical signs relate to that area. Another option is scintigraphy, with which active reactions of the spinous processes can be determined.
Treatment may be chosen depending on the severity of the condition, the owner’s financial situation and whether the aim is for the horse to return to exercise or may be retired. Kissing spines may be treated conservatively, in which case the pain is addressed medically and the horse is rested. This may be combined with physiotherapy, massage therapy, chiropractic therapy or acupuncture. However, the bony changes and inter-spinous distances would not be reversed to normal and often horses become sore again after reinstating exercise. This treatment may be an option for horses with mild kissing spines or horses that are to be retired.
Another option is surgery, which has quite a good prognosis provided the diagnosis is correct and all affected areas are treated. This relatively new surgical technique does not involve resection of bone like it was done in the past, which was quite invasive and lead to long recovery times. Instead it involves cutting the ligament between the spinous processes to allow the gaps to lengthen again. This technique can be done under a standing sedation and local analgesia. Riding can generally resume after a couple of months.
If your horse is showing signs of discomfort or reluctance to exercise, we recommend having your vet find out whether your horse may be experiencing any pain, before applying any firm training techniques to correct your horse's behaviour.