Equine Matters - Spring 2018

03 What is Kissing spines? The thoracolumbar spine of the horse is composed of eighteen thoracic vertebrae, six lumbar vertebrae and five fused sacral vertebrae. Each vertebrae has dorsal spinous processes which extend from the vertebrae upwards. In the normal horse there should be more than a 5mm gap between the summits of each dorsal spinous process and they are stabilised by the supraspinous and interspinous ligaments. In cases of kissing spines (impingement) the dorsal spinous processes are closer than they should be. The most common location of impingement is in the thoracic vertebrae, although they can occur in other locations (Figure 1). The degree of impingement can be graded as shown. When the spinous processes become close or come into contact with each other it causes pain and may cause reflex muscle spasm around the spine. Kissing spines explained Equine Matters Spring 2018 Kissing spines Heather Rea BVetMed MRCVS Cliffe Equine Vets Kissing spines, also known as dorsal spinous process impingement and over-riding of dorsal spinous processes, can be a cause of back pain, poor performance or even lameness in the horse. Kissing spines can however be present without any clinical symptoms. But what is this condition and how does it cause the symptoms that we do see? Grade 1 Narrowing of the space between two processes accompanied with some bone changes (sclerosis). Grade 2 Loss of space between two processes with moderate bone changes. Grade 3 Loss of space between two processes with severe bone changes; may have areas of bone loss. Grade 4 Loss of space between two processes with severe bone changes, bone loss and change of shape of the spinous process involved. What symptoms might we see? Often all that is reported is poor performance, which may depend on the use of the horse; this can manifest as not jumping as well as previously, lacking in impulsion or elevation of the paces or occasionally bucking. Hind limb or forelimb lameness can be seen. Some horses show signs of acute back pain such as being difficult to tack up, rearing, constant bucking and may even become dangerous to ride. If the horse has had back pain for a prolonged period of time then it may lose some topline (muscle on the back). Figure 1: Dorsal spinous processes in the box area T10-18 most common area of impingement (kissing spines) ‘There are certainly horses which have kissing spines visible on radiographs without any symptoms of pain or poor performance.’