Assessing back motion in horses by eye no easy task, findings suggest

A screenshot of the survey carried out by the study participants. In this example, frontal and lateral video stills are displayed. All nine items are scored and one box per item is ticked. Image: Spoormakers et al.

The need for objective and repeatable techniques to properly assess back motion in horses has been identified by researchers in The Netherlands.

Tijn Spoormakers and his fellow researchers, in a study published in the journal PLOS ONE, said the equine back is generally acknowledged to be a pivotal element of the horse’s musculoskeletal system, with problems a common cause of poor performance.

Therefore, clinical examination of back function is a critical skill for equine practitioners in clinical cases of lameness or poor performance, and during pre-purchase exams in presumably healthy horses.

The researchers described an experiment in which they assessed human efforts to judge equine back mobility and compared the results to those obtained through quantitative gait analysis, carried out through the use of reflective markers and video analysis.

The Utrecht University study team said lameness assessments in horses are still mostly performed using subjective methods. Visual assessment of lameness is known to have a relatively poor agreement between those carrying out the assessments, while the individuals themselves tend to show greater consistency.

However, little is known about how assessors perform in evaluating back motion, for which no objective measurement technique in a clinical setting is available thus far.

The study used 70 individuals who were either veterinarians, physiotherapists or veterinary students. Each was asked to evaluate videos of 12 healthy riding horses at walk and trot on a hard surface, in a straight line. The participants had no clinical details on the horses.

Nine parameters related to back mobility were scored: General mobility, thoracic, lumbar, lumbosacral flexion and extension and left and right thoracolumbar latero-flexion. All scored parameters were compared with results from the video analysis work, and the results from the individuals were also compared.

A month later, six randomly chosen horses were re-evaluated by 57 of the observers.

For all parameters, agreement between the different assessors was described by the study team as very poor.

The authors found that the consistency of the assessors who repeated evaluations a month later was, on average, poor.

The study team found no correlation between the visual subjective scoring of the individuals and objective gait analysis measurements.

“The main findings in this study are that in scoring equine back motion there is poor inter-individual agreement between observers, irrespective of their experience or professional background, that intra-individual agreement is on average limited, but has a high variation between individuals,” they said.

Furthermore, there was no correlation between the scoring of observers and the objective measurements. This was also the case even when some individual observers showed consistency, and was irrespective of the degree of professional experience.

“It was expected that both a board-certified orthopedic surgeon or a sports medicine diplomate would be more experienced compared to other board-certified specialists, equine practitioners, generalists or students but this could not be demonstrated,” they said.

The authors noted that poor agreement by assessors has also been recognized in other studies on the assessment of musculoskeletal system performance in both horses and humans.

The authors acknowledged some limitations to the study, including that the horses were presented only in walk and trot on a hard, straight line. “Assessment on a soft surface, lunging on both circles, canter, and a static examination were not included in this study and these additional observations might have improved agreement.

“However, although the use of circles has been proven to help in detecting front limb lameness more accurately, the agreement between experienced equine veterinarians evaluating lame horses on a straight line did not improve when circles were added to the examination.”

Nevertheless, further research is indicated to verify if additionally lunging the horse would improve the reliability of results.

“Intuitively, adding canter to this study could also have been beneficial in the evaluation of flexion and extension of the lumbosacral area.”

There might also have been some expectation bias among participants. None had information on each horse’s clinical status, and they might have expected some of the horses to have a back problem.

“It can be concluded,” they said, “that this study raises substantial concerns about the reliability of the current clinical practice of assessing back mobility in the horse on a straight line in walk and trot and hence about the value and validity of these assessments.

“A more objective way of characterizing back mobility in horses using computerized gait analysis systems, as has been developed for lameness exams, would almost certainly address these issues and research efforts into the development of such an approach are thus warranted.”

Spoormakers TJP, Graat EAM, Serra Bragança FM, Weeren PRv, Brommer H (2021) Rater agreement for assessment of equine back mobility at walk and trot compared to quantitative gait analysis. PLoS ONE 16(6): e0252536.

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

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