Kissing spine – also called dorsal spinous process impingement (DSPI) or Basstrup’s disease – occurs when the bony ‘spikes’ (dorsal spinous processes – and/or, to a lesser extent, the transverse spinous processes – see Figure 1.) at the top (or sides) of the horse’s vertebrae start to rub together, causing pain and swelling, especially on moving.
Figure 1. A typical vertebra illustrating;
- The dorsal spinous process
- The transverse spinous processes
Kissing spine lesions are most commonly located in the thoracic vertebral region (Figure 2.) where the largest dorsal spinous processes are found, but are also seen in the lumbar area.
Figure 2. The regions of the equine spine;
- The cervical vertebrae
- The thoracic vertebrae
- The lumbar vertebrae
- The sacral vertebrae
- The coccygeal vertebrae
Kissing spines is a major cause of poor performance and gait abnormality but is often not detected by the rider until it is significantly affecting performance. It is thought that this problem is related to certain types of use of the horse, and in particular its back, hence why it is frequently seen in horses jumping at speed such as eventers, hurdlers and chasers. It is likely that the condition is more noticeable in these performance horses due to the extra physical demands placed upon them, and in horses with similar skeletal conformation that are used for light exercise only, the problem may not show up at all.
In addition to poor performance, symptoms of kissing spine include resentment of certain schooling exercises, difficulty in maintaining a three-beat canter gait, irritability when the girth is tightened, resentment of pressure/grooming over his back.
A thorough history, clinical exam and observation of the horse being schooled can indicate a functional abnormality of the vertebral column, although a definitive diagnosis regarding the source of the pain can be challenging. In recent years, here have been great advances made in imaging procedures such as radiography, ultrasonography and nuclear scinitgraphy, allowing visualisation of structures and lesions that were not accessible before. As well as these imaging techniques, it is possible to inject local anaesthetic between the spinal processes where a kissing spine problem is suspected, and then to work the horse again to see if there is any improvement.
Different grades of severity can be identified from radiographs of the abnormal vertebral processes. Grade 1 lesions involve only a narrowing of the space between adjacent processes. Grade 2 lesions show an increase in bone density at the margins of the processes. In contrast, Grade 3 lesions show loss of bone adjacent to the margins, and Grade 4 lesions involve severe remodelling of the processes, due to chronic and profound irritation of the structures. These lesions can be seen in th top part of the spinal processes, where the tips may impinge on each other, but can also be seen lower down towards the body of the vertebrae. Lower lesions may involve the interspinal ligaments or be associated with osteoarthritis between adjacent vertebral bones.
It is worth keeping in mind that not all kissing spine lesions will cause pain and poor performance in every horse. These lesions are commonly found in racing thoroughbreds and seem to be tolerated in many of them. In standardbreds, kissing spine is rarely diagnosed, but when it is present, their likelihood of causing pain appears to be higher. Kissing spine can be found in performance and sport horses without back pain, and without apparently restricting back movement in any way. Therefore, in each case, the clinical significance of these lesions must be carefully assessed.
There are several treatment options available and selection will depend on the nature of the lesions, their severity (grade) and the intended future use of the horse in question. Some vets advocate the use of corticosteroid injections around the kissing spine lesion; this approach is often used in combination with a prolonged rest and rehabilitation period involving tolerated exercises and physiotherapy. Shockwave therapy has also been shown to be successful in the treatment of some cases.
For many horses, the best treatment option is surgery. During the procedure, an incision is made over the top of the spinous processes and the top half the of the process is removed (about 3 inches of bone). The bone doesn’t regrow, and the space left by the removal of the spinous process is gradually filled with fibrous tissue. The overall success of the surgical approach depends on following a comprehensive rehabilitation and recovery programme after surgery.