Rethink is needed on the way we use the term lameness, say experts

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Professor René Van Weeren
Professor René Van Weeren

It’s time for a rethink around the way we use the term “lame” to describe horses with subtle gait irregularities, according to experts in the field.

Professor René Van Weeren and his collaborators have addressed the issue in an editorial in the latest issue of the Equine Veterinary Journal, suggesting that use of the term lame to describe all horses showing asymmetry – uneven movement – is unwise.

Van Weeren, who penned the editorial which has the approval of four major research groups in quantitative gait analysis, suggests that equine lameness needs to be redefined to reflect the new digital assessment techniques that use preset parameters to detect gait asymmetries.

The traditional way to detect equine lameness is subjective, using expert visual evaluation of a horse’s gait.

Horses that are lame are described as having a disorder, defect or loss of function, and this clinical diagnosis has associated welfare implications if the horse is still asked to perform.

However, advanced computer technology is starting to change all this. Optic motion capture or the use of inertial measurement units now enable the detailed study and quantification of the horse’s gait. This is an objective assessment against preset thresholds.

Van Weeren and his collaborators point out that while these digital systems can overcome the limitations of the human eye, they simply rely on one or a number of set gait parameters to decide about lameness. This can present obstacles.

Thresholds are forcibly based on a limited reference population, which doesn’t adequately reflect the millions of horses in the world. The individual environmental and mental conditions for each horse and its day-to-day gait variations are also not accounted for.

On this basis, to use the term “lame” because a horse demonstrates a subtle gait alteration, causing it to fall below the threshold, could be inappropriate, particularly as it may not affect the horse’s welfare in any way.

Van Weeren said it was well-known that agreement on subtle lameness by visual observers, even if they are deemed experts, was meagre at best.

Studies suggest the gap between the horse-using public and the veterinary profession on questions of soundness is even wider.

Van Weeren said that when technology was used to quantify the gait of horses considered sound by their owner, a large number of these fell outside the normal range and were hence deemed lame.

In a 2016 study of 201 horses ridden regularly and functioning well in their work, 107 (53%) showed asymmetries surpassing the thresholds set for either head or pelvis asymmetry. In another study, of a total of 222 horses considered sound by their owners, an astonishing 72.5% showed movement asymmetries above previously reported thresholds while trotting in a straight line.

“Should we qualify these horses that do not comply with criteria for optimal gait during a comprehensive and critical clinical lameness examination or that fall outside the threshold values set for the automated gait analysis systems as lame?

“This question is very relevant because of the strong association in public perception between the term ‘lameness’ and impaired welfare.”

And what, he asked, do we really know about day-to-day variation in subtle gait characteristics in horses, or of variation over longer periods?

“What about the effects of the environment or even the mental condition of the horse on these measured or clinically observed asymmetries and irregularities, which are too small to impede daily use of the horse and/or participation in competitions? Can we state with certainty that these subtle gait alterations affect equine welfare to some significant extent?

“The most logical avenue to follow seems to establish whether or not those horses experience pain. That, however, is an art in itself and far from trivial.

“Even if the existence of pain can be proven, the next question arises, which is to what level the existence of pain can be deemed acceptable. There is no human athlete pursuing their career without experiencing pain,” he noted.

Beyond biology, ethics then came into the equation, Van Weeren said.

The collaborators argue that the use of the term “lameness” in relation to any subtle gait alterations is questionable in a scientific sense and may be dangerous in the more societal context due to the negative connotation of the word lameness.

“There is a strong need to better investigate the background and true meaning of these subtle gait alterations and to put them in the (largely unknown) context of normal variation, as well as to determine their true effect on equine welfare.

“As long as there is insufficient information to this respect, one should be very cautious with the use of the term ‘lameness’, and probably more cautious than in the older days when the human eye was the only available tool for the evaluation of equine gait.

“We advise strongly that researchers and clinicians should discriminate clearly between ‘asymmetry’ and ‘lameness’ and not to use these as interchangeable terms when interpreting gait analysis data.”

Lameness implied some kind of pathological aberration, most likely musculoskeletal in origin, whereas the term asymmetry was just a technical term describing a larger or smaller deviation of perfectly symmetric motion.

“Using the term ‘lame’ for any horse falling beyond thresholds set for quantitative gait analysis or not showing the ideal motion pattern when assessed clinically does not seem a wise thing to do. We should reserve the use of that term for horses deemed unfit to compete based on a comprehensive assessment of the animal that includes, but does not rely entirely on, the appreciation of the degree of gait asymmetry.”

The journal editor, Professor Celia Marr, said it was an important first step for researchers and clinicians to start to discriminate clearly between ‘asymmetry’ and ‘lameness’, and not to use these as interchangeable terms when interpreting gait analysis data.

“Asymmetry is often, but not always, a hallmark of lameness, but is not a clinical term, whereas lameness is.”

Do we have to redefine lameness in the era of quantitative gait analysis? P.R. van Weeren, T. Pfau, M. Rhodin, L. Roepstorff, F. Serra Bragança, M.A. Weishaupt. Equine Veterinary Journal 49, 567-569.

The editorial can be read online here.   

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