Spinal Processes and Associated Ligaments in Horses

The most common location of kissing spines is the vertebral segment between T10 and T18, although these lesions are also identified between L1 and L6. Abnormal findings can be seen in the dorsal part of the spinous processes where their identification is easy; they include kissing and overriding lesions. Different grades can be identified (grade 1: narrowing of the interspinal space; grade 2: densification of the margins; grade 3: bone lysis adjacent to the margins; grade 4: severe remodeling). Abnormal findings can also be seen in the ventral part of the spinous processes and may involve the interspinal ligaments or be associated with osteoarthrosis of the articular processes. Their severity can be established using the same grading system; their clinical incidence seems higher.

The incidence of kissing spines seems to vary according to the discipline/use of the horse and biomechanical effects of specific gaits and exercises on the back. In general, these lesions are commonly found in racing Thoroughbreds and seem to be tolerated in many of them. They are quite rare in Standardbreds, but when present, their likelihood of causing pain seems higher. Intermediate frequency and signs are seen in sport horses. Kissing spines can be found in performance race and sport horses without back pain and even with normal thoracolumbar active and passive mobilization. Thus, in each case, the clinical significance of these lesions must be carefully assessed. Diagnosis can be aided by injection of local anesthetic into the affected interspinous spaces. Medical management includes local injections of steroids and/or shockwave therapy, as well as rehabilitation using tolerated exercises after progressive warm-up at a slow canter. Surgical treatment has been advocated for this condition, with surgical resection of the affected spinous processes being most commonly performed and being described as efficacious in managing this condition. A number of differing techniques have been described for this surgical management.

Multiple fractures of the spinous processes of T4–T10 are sometimes seen in horses that have reared and fallen over backward. The summits and centers of ossification are fractured and displaced laterally. After the initial pain and local reaction have subsided, recovery is often satisfactory, with usually no permanent effect on performance, although a persistent deformation of the withers may require some adaptation of the saddle.

Acute or subacute desmopathies can be identified ultrasonographically, because they demonstrate dorsoventral or transverse thickening of the ligament, altered echogenicity, and obvious alteration of the linear longitudinal pattern. They can be seen both in the median plane or asymmetrically. In old or chronic injuries, the ligament often remains thicker, with a reduced echogenicity and an irregular architectural pattern. Hyperechogenic images with or without acoustic shadows are compatible with mineralization or calcification of the supraspinous ligament. Alteration of the bone surface of the top of the spinous processes indicates insertional desmopathy (enthesopathy) of the supraspinous ligament. The significance of findings can be difficult to definitively prove, because ultrasonographic abnormalities can be seen in healthy as well as injured horses.