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Evidence of kissing spine syndrome was found across a representative group of Thoroughbred racehorses in a recent study, pointing to the widespread nature of the problem.
Diseases affecting the equine back are divided into three categories – congenital deformities, soft tissue injuries and spinal injuries. Kissing spine syndrome is the most common disorder among sport horses in the last category.
It is characterized by a narrowing of the space between the spinous processes, and changes to their dorsal margins. Spinous processes are the bony projections off the back of each vertebra, providing the points of attachment for the muscles and ligaments of the spine.
This syndrome in horses most often relates to narrowing in the thoracic segment, generally between T14-T15 and T15-T16.
Researchers Darío Infante, Arnaldo Croxatto and Felipe Corrêa, writing in the journal Sustainability Agri Food Environmental Research, said there were multiple causes behind the syndrome, making it difficult to diagnose during its development.
It can occur in horses with low or normal athletic performance and with poorly defined clinical signs, because the presentation of pain may be continuous, intermittent or absent.
The study team pointed to a 2011 study involving 310 horses in which 68% were found to have kissing spine syndrome. However, the diagnosis rate has been reported in an earlier study at only 0.9%, suggesting it is highly underdiagnosed.
Corrêa and his colleagues carried out x-ray evaluations on a cross-section of 30 Thoroughbred racehorses in Chile – 10 stallions, 10 mares and 10 geldings. They took x-rays to evaluate the degree of kissing spine in the thoracic section, using a grading system of 0-7.
Stallions and mares presented with, on average, 4 affected dorsal spinous processes, unlike geldings that presented on average with 3.5.
The researchers said there was a mathematical tendency toward a higher average width of the interspinous space in the geldings in the study. This contrasted with research reported in 2009 which found a higher frequency of kissing spine among thoroughbred geldings.
Traversing the issues, the authors said horses were predisposed to back injuries because of the type of work and competition intensity to which they were exposed. Thoroughbreds were more prone when compared to other breeds because the tips of their spinous processes are closer to each other.
Back injuries have great implications for performance, and are associated with a complex and sometimes confusing clinical presentation.
“Due to its particular anatomy, the horse´s vertebral column is not designed to support significant weight on the spine,” they wrote.
“Because of a physiological and behavioral need created by man to bear weight, the equine vertebral column provides a combination of elasticity and rigidity during the biomechanics of exercise, which allows high speed activities to develop.
“The need to carry weight causes the greatest impact on the area between T14 to T16, where the rider’s weight is carried.”
The authors said a greater presence of kissing spine syndrome was found in the central segments, which supported findings in previous studies which found that the most common segment affected was T15-T16, followed by T14-T15 and T16-T17.
However, they cited other research published in 2010 which found a higher prevalence of the syndrome between T13-T14, T14-T15, T15-T16, T16-T17 and T17-T18. In another 2010 study, the prevalence was greater in T15, followed by T16 and T17 in the thoracic segment.
The distribution of the syndrome is similar in stallions but not in mares and geldings.
The authors noted that sex steroids played a role in the regulation of bone metabolism – estrogens acted by decreasing bone resorption and testosterone was responsible for strength and bone density, which was why these differences between groups may occur.
In 2006, other researchers proposed that sport horses were under constant physiological stress and drug and/or chemical substance administration because of their activity. This, it was said, could depress the immune system, altering the regulation of androgens. On this basis, measurement of hormones and blood profiles in kissing spine study groups could provide valuable information.
“These results can also allow that adequate food is provided for the activity of the horse, thus meeting the requirements of vitamins, minerals and protein needed, including bone metabolism.”
The authors also discussed the conclusions of researchers in 2010, who noted that the thoracolumbar stability was provided by the epaxial and hypoaxial muscles, so development of these muscle groups had a protective factor against kissing spine syndrome in sport horses. Small variations in these muscles could cause back changes in the sport horse.
All joints in the thoracolumbar region had limited mobility, making it difficult to detect changes when the horse was trained.
Infante is with the veterinary hospital at Universidad Mayor; Croxatto and Corrêa are with the Veterinary Medicine School at Universidad Andres Bello. Corrêa is also within the Doctoral Program in Veterinary Medicine at Universidad Andres Bello.
Radiologic findings consistent with kissing spines syndrome in Chilean thoroughbreds horses
Darío Infante Arnaldo Croxatto, Felipe Corrêa
Sustainability Agri, Food and Environmental Research 4(4), 2016: 14-17 ISSN: 0719-3726