Kissing Spines (Impingement of the Dorsal Spinous Processes)
The most common location of kissing spines in horses is the vertebral segment between T10 and T18; however, these lesions are also identified between L1 and L6. Abnormal findings can be evident in the dorsal part of the spinous processes, where their identification is easy (see kissing spines image); they include kissing and overriding lesions.
Courtesy of Dr. Sushmitha Durgam.
Different grades of kissing spine lesions can be identified:
grade 1: narrowing of the interspinal space
grade 2: sclerosis of the margins
grade 3: bone lysis adjacent to the margins
grade 4: severe remodeling
Abnormal findings can also be evident in the ventral part of the spinous processes and can involve the interspinal ligaments or be associated with osteoarthrosis of the articular processes. Their severity can be established using the same grading system.
The incidence of kissing spines varies according to the discipline/use of the horse and the biomechanical effects of specific gaits and exercises on the back.
In general, kissing-spines lesions are commonly found in racing Thoroughbreds and seem to be tolerated in many individuals.
These lesions are quite rare in Standardbreds; when present, however, they are often associated with pain in this breed.
Sport horses show kissing spines with intermediate frequency and intermediate likelihood of clinical signs.
Kissing spines can occur in racehorses and sport horses without back pain and even with normal thoracolumbar active and passive mobilization.
In each case the clinical importance of these lesions must be carefully assessed.
Diagnosis can be aided by improvement when the horse is exercised after injection of local anesthetic into the affected interspinous spaces and by scintigraphic evidence of increased radiopharmaceutical uptake at the radiographically evident kissing/overriding interspinous spaces.
Medical management of kissing spines in horses includes local injections of steroids and/or shock wave therapy, as well as rehabilitation using tolerated exercises after progressive warm-up at a slow canter.
Surgical treatment has been advocated for kissing spines if medical management is ineffective. Options include interspinous ligament desmotomy or partial surgical resection of the affected spinous processes. The appropriate surgical option depends on the severity and individual case.
Fractures of Spinal Processes in Horses
Multiple fractures of the spinous processes of T4 through T10 sometimes occur 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 from spinous process fractures is often satisfactory, with usually no permanent effect on performance. However, a persistent deformation of the withers might require some adaptation of the saddle.
Desmopathies in Horses
Acute or subacute desmopathies (also referred to as supraspinous ligament injuries) can be identified via ultrasonography, because they demonstrate dorsoventral or transverse thickening of the ligament, altered echogenicity, and obvious alteration of the linear longitudinal pattern. Supraspinous desmopathies in horses can occur both in the median plane and asymmetrically.
In old or chronic injuries, the ligament often remains thicker, with decreased echogenicity and an irregular architectural pattern. Hyperechoic regions with or without acoustic shadows are compatible with mineralization or calcification of the supraspinous ligament.
Alteration of the bone surface at the top of spinous processes indicates insertional desmopathy (enthesopathy) of the supraspinous ligament. The clinical importance of these findings can be difficult to definitively prove, because abnormalities evident on ultrasonography can occur in both healthy and injured horses.
For More Information
Derham AM, Schumacher J, O'Leary JM, Kelly G, Hahn CN. Implications of the neuroanatomy of the equine thoracolumbar vertebral column with anesthesia and complications following desmotomy of the interspinous ligament. Equine Vet J. 2021;53(4):649-655. PMID: 33336365 DOI: 10.1111/evj.13402
Also see pet owner content regarding kissing spine syndrome in horses.
