Kissing spine, officially termed impingement of the dorsal spinous processes, is a common back condition that can affect horses of any breed or age. It involves the bony projections extending upwards from the vertebrae in the horse’s back becoming too close together, touching, or even overlapping. When these structures impinge, it causes chronic inflammation and pain in the thoracolumbar region. This discomfort often leads to performance issues and behavioral changes, significantly impacting the horse’s ability to be ridden or worked.
Anatomical Basis of Kissing Spine
The horse’s vertebral column is made up of numerous bones, including the thoracic and lumbar vertebrae that form the back and loin. Each vertebra features a prominent dorsal spinous process (DSP), which is a vertical, fin-like projection of bone. These DSPs are normally separated by interspinous ligaments and muscle tissue, maintaining an even space between the bony structures.
The most common location for impingement is in the thoracic vertebrae, specifically between T13 and T18, which is the region directly underneath the saddle and the rider’s seat. This area is particularly susceptible because the angle of the DSPs changes orientation here.
When the bony projections touch or overlap, the constant friction and pressure cause pathological changes. This results in inflammation, pain, and bone remodeling, where the body attempts to strengthen the area by laying down more bone. Radiographically, this is seen as sclerosis, or increased bone density, and sometimes bone lysis, which is the destruction of bone tissue.
Recognizing the Signs
The clinical manifestations of kissing spine are highly variable, ranging from subtle changes in performance to severe behavioral reactions. Many horses with mild bony changes may not exhibit any noticeable signs, but those that do often display discomfort under saddle. A horse owner may first notice resistance when being saddled, such as flinching, tail swishing, or “girthiness” when the girth is tightened.
During ridden work, affected horses frequently display performance issues. These include:
- Unwillingness to move forward or reluctance to engage the hindquarters.
- A shortened, stiffened stride.
- Bucking, rearing, or kicking out, especially during transitions or collection.
- Refusing to jump or cross-canter.
- Difficulty maintaining a consistent gait, as they are unable to comfortably round or flex their backs.
Physical indicators are also important for recognizing the condition, particularly a hypersensitivity to touch along the back. Palpation of the spine may elicit a painful reaction, such as hollowing the back, dipping away, or muscle spasms. Over time, chronic pain and compensatory movement can lead to poor muscle development, specifically muscle wastage along the back and hindquarters. This lack of topline is often both a symptom and a factor that can worsen the condition, as the core muscles are unable to adequately stabilize the spine.
Diagnosis and Treatment Options
A veterinarian’s diagnosis of kissing spine begins with a comprehensive physical examination and lameness evaluation. The veterinarian will carefully palpate the back to identify specific areas of pain and muscle tension, and will observe the horse in motion to assess its gait and posture. Diagnostic local anesthesia is often used, where a local anesthetic is injected around the suspected painful DSPs; a temporary improvement in the horse’s movement or behavior strongly suggests that the back pain is localized to that area.
The definitive diagnosis is typically made using radiography (X-rays) of the thoracolumbar spine. X-rays reveal the degree of narrowing, touching, or overlapping of the dorsal spinous processes and show associated bony changes, such as sclerosis or bone lysis. For complex cases, nuclear scintigraphy (a bone scan) may be used to identify areas of active bone remodeling and inflammation, confirming which lesions are currently causing pain.
Medical Management
Treatment often begins with medical management aimed at reducing pain and inflammation. The most common approach involves local injections of corticosteroids, sometimes combined with a local anesthetic, directly into the spaces between the affected DSPs. These injections provide an anti-inflammatory effect to alleviate the discomfort. Systemic medications, such as muscle relaxants, may also be prescribed to help reduce the chronic muscle tension that often accompanies the condition.
Physical Therapy and Rehabilitation
Physical therapy and a structured rehabilitation program are essential for long-term management. The focus is on strengthening the horse’s core muscles and improving the flexibility of the back. Specific exercises, such as those that encourage the horse to stretch down and engage its abdominal muscles, help to lift the back and potentially increase the space between the DSPs. Specialized equipment, including resistance bands or water treadmills, can be utilized under professional supervision to facilitate core strengthening and build up the topline.
Surgical Intervention
Surgical options are generally reserved for horses that do not respond sufficiently to medical and physical management. One common procedure is the interspinous ligament desmotomy (ISLD), which involves cutting the interspinous ligament connecting the adjacent DSPs. This minimally invasive surgery, often performed on a standing, sedated horse, is thought to relieve tension and increase the space between the bony processes. A more invasive option for severe cases is the partial resection of the DSPs, where a section of the bone is surgically removed to permanently eliminate the contact.