Is the use of objective gait analysis inevitable?

Modern technology has the potential to remove bias from gait analysis but is only as good as its interpretation

25 February 2020, at 9:00am

The equine industry has seen a surge in interest, availability and use of objective gait analysis (OGA; Figure 1) for the detection of lameness in horses. The main advantage of using OGA is the potential to remove bias from clinical decision making. However, some veterinarians have expressed concerns regarding the use of OGA to detect lameness.

Lameness “threshold values” that exist with OGA (6-7mm for the head, 3mm for the sacrum) were derived by comparing OGA measurements with veterinary expert assessments following induced lameness. However, many horses deemed sound by their owners have head and/or pelvic movement asymmetries which fall outside these thresholds. Van Weeren (2017) suggested that the term “lame” should be reserved “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”.

Pfau (2019) suggested that a group of horses which all exceed the threshold values will contain a higher proportion of lame horses than a group not exceeding the thresholds. In addition, bilaterally lame horses may have values not exceeding the thresholds.

Logically, if an owner reports a drop in performance and the values lie outside the thresholds, it would seem sensible to explore the reason for the asymmetry and establish whether it is linked to the loss of performance; at least it demonstrates the limb which is producing less force than the others.

Coincidently, the threshold values also align with the confidence intervals reported when OGA is used to repeatedly assess the same horse. Therefore, if a change greater than the confidence interval is seen following diagnostic analgesia one can confidently conclude that this change is a result of the administered block.

Bathe et al. (2018) stated that lameness is a continuum rather than a simple binary (lame/not lame) concept and that inertial systems are a long way off being superior in terms of their critical analysis. Indeed, an asymmetry can be so mild that it can be difficult to detect. If this is the case, how can we ensure it is clinically relevant? It is obvious that its relevance should be assessed in the context of the horse’s breed, use, age and history and what the rider reports. As an example, a dressage rider may notice reduced hindlimb push off during a canter pirouette in one direction compared to the other well before it becomes visually evident when the horse is trotted in hand. If OGA can detect a subtle lameness, undetectable to the human eye, and those values return to the normal accepted range following diagnostic analgesia and the rider reports an improvement, this increases the security of the diagnosis. OGA gives the user confidence to embark on diagnostic analgesia in this situation and adds objectivity to the post-block assessment.

Adair et al. (2018) agreed that lameness is a continuum but by measuring it objectively we can improve precision and accuracy; they suggested that lameness does not need to be redefined. OGA is more sensitive than the human eye with respect to spatial and temporal resolution so it can detect asymmetry below that which the human eye can detect. In agreement with Bathe et al. (2018) there is more to lameness diagnosis than just asymmetry of movement; it is somewhat insulting to the users of OGA to suggest that they base their entire lameness work-up on the outcome values obtained by OGA. It is merely a complementary tool, as is ultrasonography, radiography, scintigraphy, etc. Any clinical decision should always be made with all the available evidence and in consultation with the owner, ensuring they feel their complaint, and the horse’s problem, is being addressed.

The debate continued with Van Weeren et al. (2018) arguing that OGA improves the confidence of less experienced veterinarians when embarking on lameness work-ups and that only the outcome of a full clinical evaluation justifies the use of the term “lameness”. Dyson (2019) contributed further to the debate to stress that we should be focusing on whether the horse is experiencing discomfort, thereby differentiating between pain-induced gait and behaviour. It was concluded that whilst OGA can be used, we should look at the whole horse.

In addition to asymmetry of head and pelvic movement during weight bearing and push-off, further useful information can be gained by using OGA. An example of this is the differentiation of referred and primary lameness. With the addition of a withers sensor it has been demonstrated that the direction of head and withers movement asymmetry agree in horses with a primary forelimb lameness whereas they disagree with a primary hindlimb lameness. This gives the user more confidence about which lame limb to begin blocking when faced with ipsilateral lameness. OGA has also confirmed that lameness is more variable at the beginning of the examination, blocking a normal part of the limb with pain can make the lameness worse and that we shouldn’t expect to completely eliminate the lameness/asymmetry with diagnostic analgesia.

Much of the debate about OGA focuses on the initial assessment – whether the user should rely solely on it to detect pain-induced lameness; the author has already stated we should not. However, once lameness has been detected, and a lameness work-up using diagnostic analgesia has started, improvements can be confirmed with OGA. Whilst perineural blocks may completely resolve lameness when the area of pain is desensitised, intra-articular analgesia can be less conclusive. The response to stifle blocks in particular can be modest even if demonstrable pathology is ultimately evident on either diagnostic imaging or arthroscopy.

Improvement well below 50 percent can be expected in such cases and OGA can add reassurance in confirming a subjective perception of improvement.

It is important to remember that OGA cannot lie. It has no personality and no interest in costs; it purely measures what it is programmed to measure. Like all technology, its value is only as good as its interpretation. Veterinarians are faced with this scenario every day (eg blood results, ultrasound scans, radiographs, etc) and, of course, experience is invaluable.

It would be difficult to summarise more succinctly than Emeritus Professor Derek Knottenbelt during his plenary opening lecture of the BEVA Congress in 2017: “Technology won’t replace vets... but vets who use technology logically and carefully will replace those who don’t” (Knottenbelt, 2017).

Author Year Title
Adair, S., Baus, M., Belknap, J., Bell, R., Boero, M., Bussy, C., Cardenas, F., Casey, T., Castro, J., Davis, W., Erskine, M., Farr, R., Fischer, T., Forbes, B., Ford, T., Genovese, R., Gottschalk, R., Hoge, M., Honnas, C., Hunter, G., Joyce, J., Kaneps, A., Keegan, K., Kramer, J., Lischer, C., Marshall, J., Oosterlinck, M., Radue, P., Redding, R., Reed, S.K., Rick, M., Santschi, E., Schoonover, M., Schramme, M., Schumacher, J., Stephenson, R., Thaler, R., Vedding Neilsen, J. and Wilson, D.A. 2018 Response to Letter to the Editor: Do we have to redefine lameness in the era of quantitative gait analysis. Equine Veterinary Journal, 50, pp.415-417
Bathe, A.P., Judy, C.E. and Dyson, S. 2018 Letter to the Editor: Do we have to redefine lameness in the era of quantitative gait analysis? Equine Veterinary Journal, 50, p.273
Dyson, S. 2019 Letter to the Editor: Continued debate about what constitutes lameness. Equine Veterinary Journal, 51, pp.556-556
Knottenbelt, D.C. 2017 Using the past to make the future better: the long and winding road. Plenary opening lecture, 56th British Equine Veterinary Association Congress, Liverpool, UK. pp30-31
Pfau, T. 2019 Sensor-based equine gait analysis: more than meets the eye? UK-Vet Equine, 3, pp.102-112
van Weeren, P.R., Pfau, T., Rhodin, M., Roepstorff, L., Serra Braganca, F. and Weishaupt, M.A. 2017 Do we have to redefine lameness in the era of quantitative gait analysis? Equine Veterinary Journal, 49, pp.567-569
van Weeren, P.R., Pfau, T., Rhodin, M., Roepstorff, L., Serra Braganca, F. and Weishaupt, M.A. 2018 What is lameness and what (or who) is the gold standard to detect it? Equine Veterinary Journal, 50, pp.549-551

Andy Fiske-Jackson, BVSc, MVetMed, Dipl. ECVS, FHEA, MRCVS, is a senior lecturer, RCVS and European Specialist in Equine Surgery specialising in the use of objective gait analysis in both lameness and back pain cases. He has lectured both nationally and internationally on the subject.

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