19/10/2025
Impingement of the Dorsal Spinous Processes (Kissing Spines)
Brian S. Burks, DVM
Diplomate, ABVP
Board-Certified Equine Specialist
Kissing Spines, more scientifically known as impingement of the dorsal spinous processes, is a condition where the dorsal spinous processes are too close together and can decrease athletic performance. Like other conditions of the horse, clinical relevance can be difficult to determine since horses with the worst looking radiographs may not have any pain or decrease in performance. The condition may occur due to conformation and have a genetic component.
Horses have 18 thoracic vertebrae and usually six lumbar vertebrae. Some horses and all donkeys only have five lumbar vertebrae. The dorsal spinous processes of the thoracic vertebrae increase in length to T6-7 and become shorter moving more caudally. The thoracic DSPs slope caudally, T15 is vertical and the lumbar DSPs slope cranially. The transverse processes of the lumbar vertebrae are longer
Impinged or overriding spinous processes are characterized by bone contact and narrowed interspinous spaces that induce local pain, soft tissue inflammation, boney remodeling, and bone sclerosis. The condition is most diagnosed in performance horses and Thoroughbreds. The condition is often acquired, resulting from multiple factors, including poor saddle fit and improper training, with the head too high, so that the core muscles are not engaged.
Kissing spines can be observed in diagnostic imaging, but the clinical signs vary widely between affected horses. The dorsal spinous processes are directly below the saddle and stand straight upright with interspinous ligaments between them and the supraspinous ligament runs along the top. Normal horses should have about five millimeters of space between the bones, depending on the breed and size of the horse. In horses with kissing spines, that space between the bones can become narrowed to the point of touching or overriding.
Horses, of course, have a horizontal back, unlike the vertical primate spine, so horses do not suffer from intervertebral disc disease like humans. Bony orthopedic problems in the horse impact bending, extending, and jumping. This includes both kissing spines and arthritis of the dorsal vertebral facets. Kissing spines is most found from the base of the withers caudally to the thoracolumbar junction. Arthritis is more commonly found further caudally in the spine. The most common site affected is thoracic vertebra 15 (T15), or from T13-18. This is where the angle of the dorsal spinous processes change orientation.
The most common clinical sign is a change in behavior. Horses can become irritable when asked to bend or stretch their back. This behavior can be anticipatory to an event where the horse knows it will hurt, such as racing around a barrel or jumping. The horse may constantly switch leads to become more comfortable or they may have avoidance behavior such as bucking off the rider. They may also show hypersensitivity to brushing, girthiness, bucking, rearing, head tossing, kicking out, hollowing the back, resisting the bit, cross cantering and refusing or rushing fences. The back is often palpably sore, though many horses with sore backs are sore from hindlimb lameness, usually the hock or the stifle.
Horses may be genetically predisposed to developing kissing spines, but not all horses show clinical signs. Those horses that participated in a sport that requires much flexing and bending are more likely to show clinical signs of spinous impingement compared to low impact sports.
Diagnosis begins with clinical history and a lameness evaluation. Palpation of the back is important to check for soreness, though this can sometimes be misleading as the horse may simply think you are looking for a response.
Diagnostic imaging includes both radiography and ultrasonography. Radiography can be difficult to obtain in this part of the horse, though sometimes the diagnosis is obvious. Radiography not only looks at the interspinous spacing, but also can show increased density or even cystic lesions. About 39% of horses with significant radiographic changes may not show any clinical signs, making interpretation of the entire examination important, not just the radiograph. The angle of the radiograph can also influence the apparent spacing between processes, resulting in over-diagnosis. Ultrasound is used to look for bone irregularity, and to examine the supraspinous ligament, multifidus muscles, and the facet joints at the base of the spinous process. Nuclear scintigraphy (bone scan) can be used to find areas of impingement and identify muscle damage. Any imaging modality with abnormal findings should be followed by local anesthesia to confirm the source of pain.
When diagnostic imaging has shown spinous impingement, and lameness examination has confirmed the clinical signs, the horse may, at first, undergo medical therapy. The back muscles are tight and in spasm, and this cycle needs to be stopped. Extra-Corporeal Shock Wave Therapy (ECSWT) can provide some relief to these muscles partly by down-regulation of pain receptors. Usually, multiple treatments are required. This can be combined with photobiomodulation (therapy laser) injections into the muscle.
Stall rest may help to break the pain cycle, but physical therapy is also useful. The horse can be lightly lunged, put through cavaletti exercises. There are other specific back exercises that can be used to strengthen abdominal muscles, stabilize posture, and improve mobility. Physical therapy should encourage the horse to have freedom of movement in a relaxed frame. The natural response of the horse to back pain is to extend or hollow out the trunk, which induces further closure of the impinged processes. Stretching exercises should encourage trunk flexion and lateral bending. This can be with baited stretching. Additional exercises to encourage flexed trunk posture include the sternal lift and pelvic flexion reflexes.
Joint injections can also be used. These ultrasound guided injections are placed at the top of the joint because the joint spaces are very small and difficult to enter with a needle. Injections may be with steroidal medications, platelet rich plasma, and other non-steroid treatments. This creates longer term relief.
Another drug class is bisphosphonates such as tiludronate or clodronate. These drugs have an anti-inflammatory effect at the cellular level. Some caution should be exercised when using these medications.
In some cases, surgical intervention may be necessary. In some cases, the interspinous ligament can be cut to provide relief from the pull on the bones. Desmotomy of the supraspinous ligament should be avoided, if possible, as this may destabilize the spine and perform a neurectomy so that pain is no longer felt and there is loss of proprioception.
The second surgical option considered for Kissing Spines patients is a bone reduction procedure. Bone is removed at each impinging space to create space between adjacent bones. This surgery will result in transection of the supraspinous ligament. The procedure can be done standing but is best done under general anesthesia to alleviate the weight of the abdominal viscera, which pulls the spinous processes closer together.
Management Considerations for Horses with Kissing Spines
Certain adjustments can potentially improve the horse’s comfort and ability to perform and compete successfully.
Warm-ups should be tailored to the individual horse’s needs and preferences. Some horses may need to warm up at a canter.
Weather - Adjustments may be needed to properly prepare a horse’s muscles for work in cold weather.
Pay close attention to saddle and girth fit, as it can either help or hinder treatment or management.
Nutrition is vital to a horse’s overall health and wellness, and diet can play a critical role in maintaining a healthy weight, laying a strong foundation and supporting a normal, healthy level of inflammation. Weight loss can help horses become more comfortable than they are at higher body condition scores.
Metabolic issues should be addressed to help control weight.
Dorsal spinous impingement is a difficult diagnosis to make, and treatment is often challenging. Many horses have decreased interspinous space that may predispose to back pain, but not all affected horses require treatment. Many affected horses that exhibit clinical signs return to work following medical and/or surgical treatment, along with physical therapy. The prognosis is worse for horses under five years old and horses with five or more vertebrae involved, and in cases where the impingement is secondary to spinal arthritis.
Takeaways
• Overriding dorsal spinous processes, or “kissing spines”, occur when two or more bony projections at the top of the vertebrae (dorsal spinous processes) touch or overlap.
• The exact cause is not well understood and many horses with kissing spines do not show any clinical signs. In some cases, kissing spines are secondary to other health issues.
• Affected horses may undergo medical or surgical treatment and physical therapy.
• Recovery is possible but requires time and commitment.
Fox Run Equine Center
www.foxrunequine.com
(724) 727-3481
