Challenges in assessing equine spines highlighted in study

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Marker placements in one of the study horses. Photo: Hardeman et al.
https://doi.org/10.1371/journal.pone.0222822.g001

Assessing spinal issues in horses can be challenging, say researchers, who examined equine back motion in a study.

They found that the range of motion and variation in spinal biomechanics are small and specific to individual horses. In contrast, between-horse variation is substantially higher than within-horse variation.

These findings highlight the challenges in making subjective and objective clinical assessment of spinal kinematics in horses.

Aagje Hardeman and her colleagues, writing in the open-access journal PLOS ONE, note that back problems are a common cause of poor performance in horses. However, apart from a primary back problem, lameness may also affect spinal movement.

Riders may experience consequences of back dysfunction in their mounts, either by the reluctance of the horse to bend, sidedness or abnormal saddle movement. These associations are complex.

Clinical assessment of spinal motion in horses is part of many routine clinical exams, but they remain highly subjective.

A requirement is understanding the expected normal range of motion and variability of back kinematics.

The study team set out to objectively quantify spinal kinematics in 12 horses considered sound by their owners, using optical motion capture technology.

Assessments of the same horses were carried out at the trot on three different days and different surfaces, in a straight line and on the lunge in both directions, on soft and hard surfaces. In all, each horse was trotted out 12 times for the study.

Average variation for the flexion-extension and lateral bending of the whole back was 0.8 and 1 degrees. Pelvic motion showed a variation of 1.0 degree (pitch), 0.7 degree (yaw) and 1.3 degrees (roll).

For these five parameters, a tendency was seen for more variation on the hard surface, and reduced variation with increased repetitions.

Between-horse variation was substantially higher than within-horse variation, they reported.

The researchers found that cervical lateral bending was doubled on the left compared to the right lunge.

“It has been discussed whether sidedness in horses, as in this asymmetric cervical bending, is a consequence of human handling or related to innate laterality,” they said.

“Variation in sidedness patterns between horses could influence back range of motion, perhaps particularly on the circle.”

However, body tracking was almost symmetric when comparing left and right circles, and was generally straight on straight lines, so cervical lateral bending asymmetries appear to be relatively independent from body tracking.

The researchers say the clinical examination of the equine spine is subjective and variation exists in the approach taken by practitioners, depending on experience, tradition and personal bias.

“During lameness assessment, different professionals look at different parameters, and the same is likely true for the back. Additionally, the human eye may not be capable of appreciating the small variations in movement symmetry, or discriminate between normal and pathological back movement.”

Preliminary data on agreement between veterinarians and physiotherapists assessing spinal motion showed very poor correlations, suggesting potential benefits for evaluating back kinematics objectively.

“However, our results indicate that solely relying on measurements of back range of motion might not be an effective approach for the objective quantification of back dysfunction.

“The patterns of the different variables over a stride and the symmetry of movements may turn out to be clinically more relevant. Since the movement pattern and range of motion of the back differ between gaits, evaluating the horse also in walk and/or canter could add further information to the picture.”

They suggest that more research and collaboration between veterinarians, chiropractors, engineers and specialists in the field of objective gait analysis is likely needed to develop clinically applicable methods to improve the quality of evaluation of horses presented for disorders of the neck, back and pelvis, including the possibility of machine learning.

“In conclusion,” they wrote, “range of motion and variation in spinal biomechanics are horse-specific and small, necessitating individual analysis and making subjective and objective clinical assessment of spinal kinematics challenging.”

Most of the researchers were with either the Swedish University of Agricultural Sciences or Utrecht University in the Netherlands.

Hardeman AM, Byström A, Roepstorff L, Swagemakers JH, van Weeren PR, Serra Bragança FM (2020) Range of motion and between-measurement variation of spinal kinematics in sound horses at trot on the straight line and on the lunge. PLoS ONE 15(2): e0222822. https://doi.org/10.1371/journal.pone.0222822

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

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