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Contents:
The Past: A Brief History of Gait Analysis Movement is one of the characteristics that distinguishes living organisms from inanimate objects. Although man has been fascinated by animal movement for many centuries, the complexity of locomotion defeats analysis by our natural senses. Significant progress in understanding locomotion had to await the development of technology for measuring the movement patterns (kinematics) and the associated forces (kinetics). The advent of the computer age has facilitated investigations that could not have been contemplated even 20 years ago. In the middle of the last century, the science of locomotion was greatly advanced by the use of photography. One of the most colorful characters of that era was Edweard Muybridge, who was employed by Leland Stanford, the California railroad magnate and founder of Stanford University. Stanford had a theory that a trotting horse, at some point in its stride, had all four feet off the ground simultaneously. He had tried various mechanical ways of registering the footfalls but had not been able to prove his theory. Stanford asked Muybridge to demonstrate the existence of an airborne phase by taking a photograph of his horse, Occident, who was the fastest trotter in the world at that time, having recorded a mile in 2:16¾. Although photography had not yet reached the stage of being able to capture moving objects, Muybridge rose to the challenge and produced the required picture. He then proceeded to make 781 photographic plates of moving people and animals using a series of still cameras triggered in sequence. Muybridge’s entire works, which were reprinted in 3 volumes in 1979, make wonderful reading [13]. The next major development in locomotion analysis was the advent of cine photography. The industrial revolution brought a need for a technique to analyze mechanical machinery and the manufacturing process, hence the development of cinematography. Little did anyone guess that cine films would become such a popular recreational activity! High-speed cine cameras were developed, and for many years this was the standard technique for gait analysis in horses. However, cine cameras were temperamental to use, the film was expensive to purchase and process, and the analysis was extremely tedious and time-consuming. Life became much easier with the availability of video cameras and the development of computer-based analysis systems for extracting kinematic data from videotapes. The Present: Applications of Gait Analysis in Horses Today we have a wide assortment of techniques for analyzing the movements and forces associated with locomotion, including videography, force plates, electromyography, strain gauges, pressure transducers and accelerometers. Engineering principles are used extensively in data analysis. The main objectives of gait analysis in horses are to understand normal locomotion, to characterize pathological gait, and to describe sporting performance. This article will focus mainly on the trot, which has been selected because it the gait of choice for lameness evaluation, it is the gait used to evaluate the quality of movement in warmblood horses, and it is important in the performance of a number of equestrian sports. A knowledge of normal locomotion in sound horses is a prerequisite to recognizing abnormalities associated with lameness. During every stride each limb has a stance phase and a swing phase. The swing phase makes a major contribution to the visual impression of the quality of movement, whereas the stance phase is more important in the causation and recognition of lameness. Visual appraisal by an experienced judge is part of the licensing procedure for the warmblood breeds. Correlations between the score awarded by visual appraisal and the variables measured by gait analysis have consistently shown that a long stride length and a slow stride rate are highly rated characteristics [1,12]. The judged quality of suppleness of movement correlates best with fetlock joint extension during stance; horses with high scores for suppleness show more extension of the fetlock joint. The total range of limb protraction and retraction, and the range of motion in the shoulder and hock joints also contribute to the impression of suppleness [1]. A common question in regard to selecting young horses relates to the age at which the gait characteristics are sufficiently established to predict how the horse will move as an adult. It has been shown that, by 4 months of age, foals already have the same range of motion as they will show later in life [2]. Stride and stance duration increase with age as a consequence of the increase in limb length, but the angular patterns of the limbs are stable over time. This supports the possibility of assessing gait at a young age, when the purchase price tends to be more reasonable. The individuality and stability of the limb coordination patterns has given rise to the concept of the gait fingerprint – a characteristic movement pattern that is unique to the individual horse. In Sweden there has been considerable work on trotting Standardbreds. One of the interesting findings in relation to normal gait is that, at the start of training, the majority of Standardbreds already show left/right asymmetries in the lengths and durations of the left and right steps, with individual horses differing in the direction of the asymmetries. These asymmetries become more pronounced as training progresses [11]. Laterality in horses, which has been likened to handedness in people, is revealed by asymmetries in the movement or weight-bearing patterns, which may be difficult to distinguish from asymmetries due to lameness. One of the objectives of dressage training is to overcome any natural inclination to laterality by making the horse equally strong and supple on both sides of the body. In contrast, race training seems to exaggerate the effects of the asymmetries. Visual assessment of lameness is based on recognition of left/right asymmetries in the stride. Gait analysis offers a means of quantifying the gait deficits, and monitoring the response to treatment objectively. Lameness results in differences between the left and right limbs in the timing and distance between footfalls, in the angular motion patterns, and in the forces between the limb and the ground. When evaluating horses with various weight-bearing lamenesses at a trot, a fairly consistent finding is the lack of a suspension following the stance phase of the lame limb. This is a consequence of the inability of the lame limb to raise the horse’s body weight. Normally, the trunk follows a sinusoidal motion pattern with two peaks and troughs during each complete stride; it is highest during the suspensions and lowest in the middle of the diagonal stance phases. Each diagonal catches the weight of the trunk as it sinks and reverses its direction of motion, lifting it into the next suspension phase. In a weight-bearing lameness, the lame diagonal starts to support the trunk relatively early, before it acquires much downward velocity. Throughout the stance phase of the lame limb, the trunk moves downward with the horse rolling its weight onto the sound diagonal without lifting the trunk into a suspension. The compensating limb accepts the weight of the trunk, reverses its direction of movement, and lifts it into a suspension prior to the next stance phase of the lame diagonal [3]. Therefore, the compensating limb takes over the lifting function of the lame limb. The downward movement of the trunk as it rolls over the lame limb and the exaggerated lifting by the compensating limb can be appreciated visually. Head and neck movements are one of the most obvious and reliable diagnostic signs. Traditionally, it has been assumed that lowering the head moves the center of gravity forward and vice versa. Through computer modeling, it has been shown that these static effects on the center of gravity are minimal. It is the dynamic effect of pivoting the head and neck around a rotation point at the base of the neck, resulting in an inertial interaction between the trunk and the head/neck segments, that shifts weight from a lame limb to the diagonal and contralateral limbs [14]. A consistent sign of a weight bearing lameness is that the pastern segment of the lame limb maintains a more upright orientation during the stance phase. Consequently, the fetlock joint is visibly higher and shows less extension in the lame limb than in the compensating limb. Also, the coffin joint is less flexed as a consequence of the more upright pastern segment. Maximal fetlock extension is directly correlated with maximal vertical (weight bearing) force on the limb. Thus the distal joints reflect the weight-bearing function of the limbs. The proximal joints, on the other hand, are more involved in cushioning the weight acceptance. Kinematic analysis quantifies the clinician’s subjective impression of a lameness, whereas analysis of the ground reaction forces (GRFs) using a force plate detects changes in weight bearing and propulsion. Force analysis is a sensitive technique for detecting subtle lamenesses, though the discriminating ability between different lamenesses is poor. A range of fore limb problems (sole pressure, superficial digital flexor tendinitis, suspensory desmitis, carpal fractures) show an identical alteration in the GRF pattern consisting of reductions in the vertical (weight-bearing) force and in the braking component of the cranio-caudal force in the lame limb with compensatory increases in the opposite limb. So although the force plate is sensitive to gait asymmetries, it may not be a good way of differentiating between different types of lameness. In the gait laboratory at MSU, we are combining information from video and force plate analyses using a technique called link segment modeling [8]. This allows us to calculate the net joint moment (torque) at each joint, the work performed across the joints and the energy generated and absorbed over a period of time. We are using this technique to compare the mechanical energy expended at each joint during normal and pathological gait. Our preliminary results show that, like pathological gaits in human subjects, lame horses use more energy than normal, especially in the proximal joints, which are more dependent on active muscular contraction than the distal joints. Our model can be applied to quantify lameness, to assess the effects of different therapies, and to monitor recovery, and we are hoping that it will be a more powerful diagnostic technique than either video or force plate analysis. As an example, by comparing the gait of horses before and after the development of superficial digital flexor tendinitis, we have shown that the lame fore limb has very similar stance phase kinematics to the normal condition (before the horse became lame), with the exception of the pastern segment which is more upright in the lame limb. The GRF is similar in direction but reduced in magnitude in the lame limb. The compensating fore limb, however, shows much more marked changes both in the limb position and in the orientation of the GRF in the stance phase. This makes it easy to see how compensating lamenesses develop. Further analysis with the link segment model showed that in the lame limb there was a marked reduction in the storage and release of elastic energy at the fetlock joint, together with an increase in energy generation at the shoulder joint. Studies of Sporting Performance Equestrian sports are undergoing explosive growth. Gait analysis is being use to develop a better understanding of the physical demands of different sports, especially with regard to improving performance and understanding the mechanics of sport specific lamenesses. The characteristics of the walk, trot and canter have been described, and it has been shown that dressage horses can be trained to dissociate changes in stride rate from changes in stride length [4-6]. Consequently, transitions between the collected, working, medium and extended gaits are achieved almost entirely as a result of adjusting the stride length, while maintaining the same stride rate (or tempo). We are applying our link segment model to investigate how collection and self carriage are achieved. These terms refer to the carriage of the trained dressage horse, in which the hindquarters are lowered as a result of greater joint flexion, while the forehand and neck are raised from the shoulder. Traditionally, collection was thought to involve a shifting the center of gravity toward the hindquarters. Our results show that this occurs in some, but not all, horses. A more consistent finding is that, during collected work, the fore limbs show an increase in the braking cranio-caudal force. This is combined with an early peak in vertical GRF, to push the forehand backward and upward. Therefore, the fore limbs play an active role in achieving self-carriage. The changes associated with the development of self-carriage and collection are the opposite of the changes that occur in a fore limb lameness, so it is easy to understand why a mild lameness would have a marked effect on dressage performance. Descriptions of the timing and distance characteristics of the trot stride have shown that the diagonal limbs do not move in exact synchrony, and the term diagonal advanced placement is used to describe the asynchrony. The fore hoof contacts and leaves the ground earlier than the diagonal hind limb (negative diagonal advanced placement) in Standardbreds trotting at racing speed, and the time between fore and hind contacts increases with speed [10]. In sport horses, it is considered desirable for the hind limb to contact the ground before the diagonal fore limb (positive diagonal advanced placement), since this is thought to be indicative of a well-balanced horse. The Future: Applications of New Technology The computing power that is now available has greatly enhanced our capabilities, and I believe the next few years will see some exciting advances in our understanding of normal and pathological gait. Through the establishment of the McPhail Dressage Chair in Equine Sport Medicine, MSU is poised to be a leader in this field. Our new equine locomotion laboratory is equipped with computerized video analysis and a large force plate that has been strengthened to withstand forces as high as those of a galloping horse. Gait analysis has advanced to the point where it can be used as an adjunct to clinical lameness examination, and as an objective means of monitoring recovery from lameness. In performance horses, gait analysis can measure the degree of collection and self-carriage, it can quantify changes in performance over time, and it can detect deteriorations in performance that might be the first signs of subclinical lameness. These wide ranging capabilities suggest many fruitful avenues of research for gait analysis in the future. 1. Back W, Barneveld A, Bruin G, Schamhardt HC, Hartman W. Kinematic detection of superior gait quality in young trotting warmbloods. Vet Quart. 1994;16, Suppl 2:S91-96. 2. Back W, Schamhardt HC, Hartman W, Bruin G, Barneveld A. Predictive value of foal kinematics for the locomotor performance of adult horses. Res Vet Sci. 1995;59:64-69. 3. Buchner HHF, Savelberg HHCM, Schamhardt HC, Barneveld A. Head and trunk movement adaptations in horses with experimentally induced fore- or hindlimb lameness. Equine Vet J. 1996;28:71-76. 4. Clayton HM. Comparison of the collected, working, medium and extended canters. Equine Vet J. 1994;Suppl 17:16-19. 5. Clayton HM. Comparison of the stride kinematics of the collected, medium, and extended walks in horses. Am J Vet Res. 1995;56:849-852. 6. Clayton HM. Comparison of the stride kinematics of the collected, working, medium and extended trot in horses. Equine Vet J. 1994;26:230-234. 7. Clayton HM. Effect of added weight on landing kinematics of jumping horses. Equine Vet J. 1997;Suppl 23:50-53. 9. Drevemo S, Dalin G, Fredricson I, Hjerten G. Equine locomotion. 1. The analysis of linear and temporal stride characteristics of trotting Standardbreds [to detect lameness]. Equine Vet J. 1980;12:60-65. 10. Drevemo S, Fredricson I, Dalin G, Bjorne K. Equine locomotion. 2. The analysis of coordination between limbs of trotting Standardbreds. Equine Vet J. 1980;12:66-70. 11. Drevemo S, Fredricson I, Hjerten G, McMiken D. Early development of gait asymmetries in trotting Standardbred colts. Equine Vet J. 1987;19:189-191. 12. Holmstrom M, Fredricson I, Drevemo S. Biokinematic differences between riding horses judged as good and poor at the trot. Equine Vet J. 1994;Suppl 17:51-56. 13. Muybridge E. Human and Animal Locomotion. New York: Dover Publications; 1979. 14. Vorstenbosch MATM, Buchner HHF, Savelberg HHCMeal. Modeling of compensatory head movments in lame horses. Am J Vet Res. 1997;58:713-718. |