F.M. Serra Braganca

Do we have to redefine lameness in the era of quantitative gait analysis

For ages, horses have been divided with respect to the functional status of their locomotor system in those classified as sound and those considered lame. This dichotomy has been and still is used by both the users of horses, irrespective of discipline, and veterinarians and there is a general perception common to both categories that lame horses should be considered unfit to perform, which implies that their continued use raises a welfare issue. Whereas seemingly very useful and reassuringly simple, the matter is more complicated than that, as this approach immediately raises some questions. The first of these is how lameness should be defined. There are several definitions of lameness, including: “Lameness is an indication of a structural or functional disorder in one or more limbs or the back that is evident when the horse is standing or in movement” [1]; “Lameness is simply a clinical sign – a manifestation of the signs of inflammation, including pain, or a mechanical defect – that results in a gait abnormality characterized by limping” [2]; and “An alteration of the normal gait due to a functional or structural disorder in the locomotor system” [3]. There are more, but virtually all mention some disorder, defect or loss of function, hence a pathological condition, which makes lameness into a clinical problem. The second question is how lameness is detected, as this determines whether lameness (and thus a pathological condition) should be deemed present or not. The classical way to detect lameness has always been (and still is the mainstay in clinical practice) the visual evaluation of the gait of the horse under a number of different conditions whereby the presence or absence and degree of asymmetries is not the sole, but by far the most commonly used and most important criterion. Here, we enter a grey area, as it is well-known that interobserver agreement on subtle lameness, even if these observers are deemed experts, is meagre at best [4–7]. Another issue is that the standard lameness work-up protocol may vary from a simple trot-up on a hard surface with or without additional circling [8] to meticulous protocols including extensive assessments on hard and soft surface at all gaits and ridden [9]. As in the detection of osteochondrosis lesions, where horses may be declared ‘free of osteochondrosis’ after checking the hock, stifle and possibly the fetlock joints but may very well have lesions in other joints of the body [10], more subtle gait irregularities may be detected when horses are screened in more detail, making the qualification ‘sound’ much less absolute than generally perceived. The disagreement on existence, localisation and degree of subtle lameness is not only limited to within the veterinary profession when examining horses presented for some kind of presumed locomotion or general performance disorder. The gap between the horse-using public and the veterinary profession seems to be even wider. A recent study used a population of 57 riding horses of different levels that were classified as ‘owner-sound’, i.e. the horses were in regular use without any complaints regarding their locomotor system from their riders or trainers and without encountering problems in competition due to perceived lameness. After a meticulous clinical examination, 37 (65%) were deemed lame. Interestingly, of the remaining 20 sound horses, another 6 were found to be lame at a re-examination 14 days later, bringing the total number of lame horses in this supposedly sound population to 42 or 75% [9]. Interest in the gait of horses has a long history [11,12] and new developments such as the invention of photography or the introduction of cine film have always rapidly been used to further our understanding of equine gait [13,14]. The advent of computer technology in the modern era has enabled the detailed study and quantitation of the horse’s gait [15] and in more recent times a variety of techniques has been developed, for the major part based on optic motion capture or the use of inertial measurement units (for a review, see [16]). After lingering in the laboratory environment for long due to technical and practical constraints, more recently, some of these techniques have become available for routine clinical use and are currently being used in an increasing number of places. These systems overcome the issue of limited temporal and spatial resolution of the human eye and consequently the low intraand above all interobserver agreement of the classical subjective lameness assessment. However, whereas human individuals are known to be excellent in pattern recognition [17], these systems rely on one or a number of gait parameters to decide about lameness or not. In the current systems, this is typically done by symmetry measurements and the application of certain thresholds to these values [18]. Also, when these objective systems are used to quantify gait of ‘owner-sound’ horses, a large number of these fall outside the normal range and are hence deemed lame. In a study by Rhodin et al. [19] 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 ‘owner-sound’ horses, an astonishing 72.5% showed movement asymmetries above previously reported asymmetries thresholds while trotting on the straight [20]. It seems, therefore, that there is some agreement between the advanced, subjective clinical gait assessment based on expert opinion and the outcome of threshold-based objective asymmetry measurements by modern gait analysis techniques with respect to a high prevalence of subtle gait alterations. However, 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. Thresholds are forcibly based on a limited reference population and do only to a certain extent reflect the millions of horses in the world. Further, depending on the bandwidth chosen, they will always contain only a limited percentage of any normally distributed population, which can have great consequences for individual cases. With respect to the clinical assessment: to what extent are we looking for horses with an optimal gait under all circumstances, rather than for those with a clinically acceptable gait? Not unimportantly, what 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 issue is not that easy and we have far more than 50 shades of grey here. 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. Apart from the fact that horses, like human individuals, have different pain thresholds, there are various forms of pain. Direct peripheral pain may be relatively easy to detect, but in chronic conditions (which are very frequent in equine musculoskeletal pathology) pain pathways may have been altered and pain sources may have become different and much less easy to detect [21]. 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. It would be more than na€ıve to suppose that the situation for the horse would, or even could, be different. But where should the line be drawn and based on what criteria? Here, also ethics come in beyond the biology. It can be concluded that the interpretation of the subtle asymmetries or gait irregularities that can be detected through either very comprehensive clinical examinations by highly experienced orthopaedists or are (with increasing frequency) detected by the various asymmetry-

The development of locomotor kinetics in the foal and the effect of osteochondrosis

Summary Reason for performing study Foals stand and walk immediately after birth, but insight into the subsequent longitudinal development of their gait kinetics in the early juvenile phase and the possible influence of osteochondrosis thereon is lacking. Objectives To quantify gait kinetics in foals during the first half year of life, taking into account their osteochondrosis status. Study design Prospective, cohort study performed at a single stud farm. Methods Pressure plate measurements at walk and trot from 11 Dutch Warmblood foals during the first 24 weeks of life were used to determine body mass normalised peak vertical force, normalised vertical impulse and stance duration. Coefficients of variation of peak vertical force and stance duration were used as measures for gait maturity. Radiographs of tarsocrural and femoropatellar joints were taken at age 4–6 weeks and after 6 months to check for osteochondrosis. A linear mixed model was used to determine the effects of age, limb, presence of osteochondrosis and speed on gait parameters. Results Mean walking and trotting velocity increased over time as did stance duration and normalised vertical impulse, normalised peak vertical force values however remained relatively constant. During the first weeks of their life only the coefficient of variation of stance duration decreased significantly, while the coefficient of variation of peak vertical force did not. None of the foals was visibly lame, but the presence of osteochondrosis resulted in a temporarily but significantly reduced normalised peak vertical force. Main limitations This study is a relatively small sample size of one breed from a single stud farm. A stand‐alone pressure plate was used and body mass was estimated rather than measured. Conclusions Despite being precocious, foals need time to mature their gait. During growth, velocity at walk and trot increases, but normalised peak vertical force remains relatively constant. Although not visibly lame, a temporary reduction in normalised peak vertical force was detected in osteochondrosis positive foals using a pressure plate.

On the brink of daily clinical application of objective gait analysis: What evidence do we have so far from studies using an induced lameness model?

Quantitative gait analysis has the potential to offer objective and unbiased gait information that can assist clinical decision-making. In recent years, a growing number of gait analysis systems have come onto the market, highlighting the demand for such technology in equine orthopaedics. However, it is imperative that the measured variables which are used as outcome parameters are supported by scientific evidence and that the interpretation of such measurements is backed by a proper understanding of the biomechanical principles of equine locomotion. This review, which is based on studies on experimentally induced lameness, summarises the currently most widely used methods for gait analysis and the available evidence concerning gait parameters that can be used to quantify gait changes due to lameness. These are discussed regarding their current and future potential for routine clinical application.

Mouldable, thermoplastic, glue‐on frog‐supportive shoes change hoof kinetics in normal and obese Shetland ponies

Summary Background Obesity and hyperinsulinaemia are frequently encountered in the equine population and risk factors for the development of laminitis. There are many options for hoof support that claim a beneficial effect, but often the scientific evidence is scarce. Objectives To quantify the effect of frog‐supportive shoes on hoof kinetics in normal and obese ponies. Study design Controlled in vivo trial. Methods Ten Shetland mares (n = 10) with a normal (n = 5) or obese (n = 5) body condition were led over a dynamically calibrated pressure plate before (T0), immediately after (T1) and 72 h (T2) after application of the shoes. The following locomotor variables were measured: stance duration (StDur), vertical impulse (VI), peak vertical force (PVF), time to PVF and time from PVF to lift off. The hoof print was divided into a toe and heel region and the StDur toe–heel index was calculated. The toe–heel hoof balance curves of the vertical force were plotted throughout the stance phase. Results The VI and PVF increased significantly 72 h after application of the shoes, when compared with T0 and T1. The StDur toe–heel index and toe–heel balance curves were significantly different between the normal and obese ponies. These variables became more comparable between the groups after application of the frog‐supportive shoes. Main limitations It would have been interesting to measure the effect of the shoe in patients with acute laminitis. However, this would have had major welfare implications. Conclusions The obese ponies moved more carefully than the normal group, demonstrated by a decreased loading of the toe area. The data illustrate that the ponies became more comfortable 72 h after application of the shoes, with a pronounced effect in the obese group. Thus, these results suggest that frog‐supportive shoes could be beneficial, especially for obese ponies.

The development of hoof balance and landing preference in the post-natal period

Summary Background Foals can follow the herd within hours of birth, but it has been shown that kinetic gait parameters and static balance still have to mature. However, development of dynamic balance has not been investigated. Objectives To objectively quantify landing and pressure pattern dynamics under the hoof during the first half year of life. Study design Prospective, cohort study performed at a single stud farm. Methods Pressure plate measurements at walk and trot from ten Dutch warmblood foals during the first 24 weeks of life were used to quantify toe‐heel and medial‐lateral hoof balance asymmetry indexes and to determine preferred landing strategy. Concurrently, radiographs of the tarsocrural and femoropatellar joints were taken at 4–6 weeks and after 6 months to check for osteochondrosis. A linear mixed model was used to determine the effects of time point, limb pair (front/hind), side (left/right) and osteochondrosis status of every foal. Results At 25% of stance duration at walk, front limbs were more loaded in the heel region in weeks 6–20 (P≤0.04), the medial‐lateral balance was more to the lateral side from week 6 onwards at both walk and trot (P≤0.04). Landing preference gradually changed in the same directions. Variability in pressure distribution decreased over time. (Subclinical) osteochondrosis did not influence any of the measured parameters. Main limitations This study is limited by the relatively small sample size only containing one breed from a single stud farm. Conclusions Dynamic hoof balance in new‐born foals is more variable and less oriented towards the lateral side of the hoof and to the heel than in mature horses. This pattern changes gradually during the first weeks of life. Knowledge of this process is essential for the clinician when considering interventions in this area in early life.

Lateral movement of the saddle relative to the equine spine in rising and sitting trot on a treadmill

Saddle slip, defined as a progressive lateral displacement of the saddle during ridden exercise, has recently been given attention in the scientific press as a potential sign of lameness. The aim of this study was to objectively quantify the normal lateral movement (oscillations) of the saddle relative to the horse in non-lame horses, and associate this movement to the movements of the horse and rider. Data from seven Warmblood dressage horses competing at Grand Prix (n = 6) or FEI Intermediate (n = 1) level, ridden by their usual riders, were used. Simultaneous kinetic, kinematic and saddle pressure measurements were conducted during sitting and rising trot on a force-measuring treadmill. The maximum lateral movement of the caudal part of the saddle relative to the horses spine (MAX) was determined for each diagonal step. A mixed model was applied, with MAX as outcome, and T6 and S3 vertical position, rigid body rotation angles (roll, pitch, yaw) of the horse’s and rider’s pelvis, vertical ground reaction forces, saddle force, and rider position (rising in rising trot, sitting in rising trot or sitting in sitting trot) as explanatory variables. The least square means for MAX were 14.3 (SE 4.7) mm and 23.9 (SE 4.7) mm for rising and sitting in rising trot, and 20.3 (SE 4.7) mm for sitting trot. A 10 mm increase in maximum pelvic height at push off increased MAX by 1.4 mm (p<0.0001). One degree increase in rider pelvis roll decreased MAX 1.1 mm, and one degree increase in rider pelvis yaw increased MAX 0.7 mm (both p<0.0001). The linear relationships found between MAX and movements of both horse and rider implies that both horse and rider movement asymmetries are reflected in the lateral movements or oscillations of the saddle in non-lame horses.

Vertical movement symmetry of the withers in horses with induced forelimb and hindlimb lameness at trot

Summary Background The main criteria for lameness assessment in horses are head movement for forelimb lameness and pelvic movement for hindlimb lameness. However, compensatory head nod in horses with primary hindlimb lameness is a well‐known phenomenon. This compensatory head nod movement can be easily misinterpreted as a sign of primary ipsilateral forelimb lameness. Therefore, discriminating compensatory asymmetries from primary directly pain‐related movement asymmetries is a prerequisite for successful lameness assessment. Objectives To investigate the association between head, withers and pelvis movement asymmetry in horses with induced forelimb and hindlimb lameness. Study design Experimental study. Methods In 10 clinically sound Warmblood riding horses, forelimb and hindlimb lameness were induced using a sole pressure model. The horses were then trotted on a treadmill. Three‐dimensional optical motion capture was used to collect kinematic data from reflective markers attached to the poll, withers and tubera sacrale. The magnitude and side (left or right) of the following symmetry parameters, vertical difference in minimum position, maximum position and range‐up were calculated for head, withers, and pelvis. Mixed models were used to analyse data from induced forelimb and hindlimb lameness. Results For each mm increase in pelvic asymmetry in response to hindlimb lameness induction, withers movement asymmetry increased by 0.35–0.55 mm, but towards the contralateral side. In induced forelimb lameness, for each mm increase in head movement asymmetry, withers movement asymmetry increased by 0.05–0.10 mm, in agreement with the head movement asymmetry direction, both indicating lameness in the induced forelimb. Main limitations Results must be confirmed in clinically lame horses trotting overground. Conclusions The vertical asymmetry pattern of the withers discriminated a head nod associated with true forelimb lameness from the compensatory head movement asymmetry caused by primary hindlimb lameness. Measuring movement symmetry of the withers may, thus, aid in determining primary lameness location.

Quantification of the effect of instrumentation error in objective gait assessment in the horse on hindlimb symmetry parameters

Summary Background Objective gait analysis is becoming more popular as a tool assisting veterinarians during the clinical lameness exam. At present, there is only limited information on the effect of misplacement of markers/motion‐sensors. Objectives To investigate and describe the effect of marker misplacement on commonly calculated pelvic symmetry parameters. Study design Experimental study. Methods Each horse was equipped with custom‐made devices consisting of several reflective markers arranged in a predefined manner with a reference marker correctly positioned regarding the anatomical landmark and several misplaced markers along the sagittal and transverse planes. Linear regression analysis was used to estimate the effect of marker misplacement. Results For the tubera sacrale, each cm of left/right misplacement led to a difference in minimum position of the pelvis (PDmin) of ±1.67 mm (95% CI 1.54–1.8 mm) (P<0.001); maximum position of the pelvis (PDmax) was affected by ±0.2 mm (95% CI 0.071–0.33 mm) (P = 0.003). With respect to cranial/caudal misplacement, each cm of misplacement resulted in a PDmin difference of ±0.04 mm (95% CI −0.09 to 0.16 mm) (P = 0.56) and a PDmax difference of ±0.008 mm (95% CI −0.13 to 0.12 mm) (P = 0.9). For the tubera coxae, each cm of vertical misplacement led to a difference in the displacement amplitude between left and right tubera coxae (Hip‐Hike_Diff) of ±1.56 mm (95% CI 1.35–1.77 mm) (P<0.001); for the cranial/caudal misplacement, this was ±0.82 mm (95% CI 0.66–0.97 mm) (P<0.001). Main limitations Only three horses were used in this experiment and the study design did not permit to determine the influence of marker misplacement on the evaluation of different degrees of lameness. Conclusions Marker misplacement significantly affects calculated symmetry parameters of the pelvis. The observed errors are overall small but significant. In cases of mildly asymmetrical horses, this error might influence the decision‐making process whereas in more severe asymmetries, the influence of the error effect may become less significant.