Lameness: latest thinking on diagnostic challenges

The challenges associated with lameness identification through subjective gait evaluation are well known.

The use of objective gait assessment in both research and clinical cases has increased dramatically in the past few years, although much controversy exists over whether objective gait assessment could or should ever replace subjective evaluation.

While objective gait evaluation is undoubtedly more sensitive than the human eye at identifying asymmetry of movement and reduces observer bias when used to assess the response to diagnostic analgesia, the present stage of technological development, and our limited scientific knowledge on movement patterns of sound and lame horses, is not sufficient to support its use in clinical practice without caution, and in conjunction with careful subjective appraisal.

Serra Bragança et al (2017) investigated the potential effects of marker misplacement on kinematic data in three horses with mildly asymmetrical pelvic movement. They demonstrated that left-right misplacement of tuber sacrale markers and proximal-distal misplacement of tuber coxae markers significantly affected symmetry parameters in these horses.

Similarly, Pfau and Weller (2017) demonstrated the potential for misleading results due to inaccurate sensor positioning using a smartphone capable of quantifying pelvic movement symmetry positioned over the tuber sacrale. Both of these studies indicate misplacement could lead to false-negative or false-positive results and, therefore, misdiagnosis.

Inadequacies in lameness definitions

Several existing definitions of lameness were discussed, and as established by the authors, some inadequacies exist in the wording of many of them. They compared one study by Greve and Dyson (2014), where subjective lameness evaluation identified 47% of a group of “owner-sound” horses showed gait abnormalities consistent with lameness, to two other studies where objective lameness evaluation identified asymmetry of movement in 53% and 72.5% of “owner-sound” horses (Rhodin et al, 2016 and Rhodin et al, 2017 respectively).

In the editorial, it is proposed gait alterations or asymmetries in groups of horses deemed to be sound by their owners may not be experiencing pain, or that pain-causing gait alteration or asymmetry to a degree that is unrecognised by the owner, may not compromise horse welfare.

From an objective gait evaluation perspective, they suggest that because lameness implies compromised welfare, it should be redefined and that the terms “asymmetry” and “lameness” should be used separately – and that only horses unfit to compete should be described as lame. However, the ability of owners and riders to identify signs consistent with lameness or pain is somewhat limited, so the suggestion that the welfare of horses showing signs consistent with lameness, or asymmetrical movement deemed sound by their owners, is not compromised is unjustified.

Owners and riders often do not recognise the signs of pain-causing lameness or poor performance – passing them off as training, rider or behavioural issues (Dyson and Greve, 2016). In itself this may compromise horse welfare, and may lead to late presentation for veterinary evaluation, by which time the problems are longstanding, have possibly deteriorated and may be accompanied by secondary conditions, leading to a poorer prognosis.

As discussed in the editorial, the term lameness has negative connotations with some people with respect to horse welfare. This is a misinterpretation of a clinical term that does not imply severity, temporality or effect on welfare. Lameness can be simply defined as an alteration of gait to avoid pain.

Instead of redefining lameness to fit in with owner and rider perceptions of lameness, the horse-owning public should instead be educated by the veterinary profession to clarify the meaning of lameness, and diminish misguided negative perceptions. Moreover, to separate the terms asymmetry and lameness would be misleading, because they are not necessarily separate entities, although non-pain-related laterality probably does occur.

Markers of lameness

The most frequently used markers of lameness for both subjective and objective gait evaluation are those of pelvic and poll movement asymmetries (commonly known as “hip-hike” and “head-nod”, respectively). These are only two gait abnormalities that may indicate pain-causing lameness or poor performance.

Not all horses with pain-causing lameness display these adaptations; for example, a horse with bilaterally symmetrical pain-causing lameness will not show movement asymmetry. This is a major limitation, particularly to objective lameness evaluation.

Many other signs of pain or gait adaptations can be readily evaluated subjectively. Earlier this year, Mullard et al (2017) developed and validated the application of an ethogram to describe facial expressions in ridden horses with and without pain-causing lameness. The ethogram was taught to, and applied by, a group of veterinarian surgeons, veterinary professionals and horse owners using photographs of lame and non-lame horses.

Facial features evaluated in the ethogram included the eyes, ears, mouth, nostrils, muzzle and head position. The ethogram was reasonably repeatable among observers. The group then assessed whether the ethogram could be applied blindly to images of lame and non-lame ridden horses and be used to distinguish between the two groups (Dyson et al, 2017).

A pain score was assigned to each facial feature. Total pain scores were significantly higher in lame than non-lame horses (p<0.001). Ear position (flat back, one forward and one back or one to the side and one back), eyes (intense stare, muscle tension around the eye, eye partially or fully closed, scleral show), mouth (lips separated showing teeth [may also be separated] or gums, with or without the tongue being visible, asymmetrical position of the bit), tilting the head and being severely above the bit were the most reliable distinguishers of lame horses (Figure 1).

A whole horse ethogram of 70 behavioural markers that were repeatable (one trained observer) was subsequently developed and applied blindly to videos of lame and non-lame horses (Dyson et al, 2018). Twenty-four behavioural markers differed significantly between the lame and non-lame horses. In addition to facial features (ear position, mouth opening, tongue out, eye expression and position, head above the bit, tilting the head), an unwillingness to go forward, resisting, hurrying, crookedness, changing the gait spontaneously, poor quality of canter, stumbling and toe dragging occurred significantly more in the lame than non-lame horses (p<0.05; Figure 2).

The total scores of behavioural markers out of 24 were greater in lame (maximum 14, median and mean 9) than non-lame horses (maximum 6, median and mean 2). The facial and whole horse ethograms have the potential to greatly advance subjective gait evaluation, not only by veterinary surgeons, but also owners, riders and trainers.

The positive impact of the ethograms for aiding in the identification of subtle or multilimb lameness, or pain-causing poor performance, and also on identification of musculoskeletal pain in the ridden horse by the horse-owning public or less experienced veterinary surgeons, could be huge for equine welfare, earlier identification and presentation for investigation, and improved prognosis and response rates to treatment.