Abnormal bony changes common in the neck of horses – study

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File image. © Mike Bain

Abnormal bony changes were found to be common in the neck joints of horses used in an American study.

Kevin Haussler and his colleagues, writing in the open-access journal PLOS ONE, note that neck pain and stiffness are becoming more commonly recognized problems in horses due to increased awareness of their potential to harm athletic performance.

The use of detailed spinal evaluation procedures and improved diagnostic imaging has also helped shine a light on the issue.

Haussler, Roy Pool and Hilary Clayton set out to explore any abnormal bone-related changes affecting the joint surfaces, margins and adjacent soft tissue attachments in the cervical (neck) and first three thoracic vertebrae.

They said the first three thoracic vertebrae were included due to increased awareness of the clinical relevance of disease affecting this region in performance horses

The necroscopic evaluations were made on 55 horses who died or were euthanized at a veterinary teaching hospital for reasons unrelated to neck issues. Indeed, no primary neck complaints were known among the horses.

The horses represented a diverse population of breeds, including miniature horses, ponies, Arabian, Morgan, Missouri Foxtrotter, Quarter Horses, Paint, Appaloosa, Thoroughbred, Warmbloods, Draft horses, and crossbreds. The average age was 13 ± 7 years.

The study team found that 72 percent of articular (joint) processes had bony changes that were considered abnormal.

Osteophyte formation was the most common bony change noted. These are bony lumps (bone spurs) that grow on the bones of the spine or around the joints.

Just 28% of the articular processes examined were assessed as normal, 45% had abnormalities graded as mild, 22% were graded moderate and 5% were assessed as severe.

The highest prevalence of mild changes was localized to the C3-C6 vertebral levels; moderate changes to C6-T2; and severe changes to C2-C3 and C6-T2.

The severe changes at C6-T2 likely reflect increased local stresses due to the transition from a freely moveable cervical region to a more rigid cranial thoracic region.

Older horses and taller horses were considerably more likely to have more severe abnormalities.

The study team said the prevalence of abnormal bony changes was high. There were a wide variety of abnormal changes of varying severity seen across all the vertebral levels examined.

“The clinical significance of the described lesions is unknown,” they said.

Discussing their findings, the researchers said the overall prevalence of 72% was higher than a previous study that found 48% of clinically normal horses had moderate to severe degenerative changes of the articular processes.

They stressed that their findings showed a high prevalence of mild grades of disease and that the clinical significance of the changes was not known.

“It is possible that some of the horses had signs of neck pain or stiffness as they did not have a thorough physical examination of the cervicothoracic region prior to death.”

There are certainly some types of bony changes that are more clinically relevant or more readily visualized on diagnostic imaging than other types, they added.

The grade of bone-related changes was positively associated with both age and wither height due to larger horses being predisposed to increased local stresses associated with a longer and heavier head and neck.

File image. © Mike Bain

The authors argued that more descriptive terms other than “osteophytes” are needed to fully capture the spectrum of disease localized to joint processes.

“Unfortunately, there are a wide variety of confusing and poorly defined pathologic and radiographic terms used to describe joint disease within the cervical region of horses.

“There is a need to develop standardized descriptions and terminology of abnormal gross and radiographic findings to better characterize and assess the wide spectrum of osseous (bone) and soft tissue changes within the cervical region, especially with the advent of advanced imaging technology.

“It is hoped that some of the descriptors and terminology used in this pathoanatomical study will contribute to that need.”

Haussler is with Colorado State University; Pool is with Texas A&M University; and Clayton is with Michigan State University.

Haussler KK, Pool RR, Clayton HM (2019) Characterization of bony changes localized to the cervical articular processes in a mixed population of horses. PLoS ONE 14(9): e0222989. https://doi.org/10.1371/journal.pone.0222989

The study, published under a Creative Commons License, can be read here

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