Gait Analysis for Horses
The various applications of this technology also have grown. One of the prime functions continues to be evaluation of lameness, but it also has been highly important in the field of research; recording, for example, just how the hock joint functions in the working horse.
A leading researcher during this technology growth spurt has been Hilary Clayton, BVMS, PhD, MRCVS, Mary Anne McPhail Dressage Chair in Equine Sports Medicine at Michigan State University.
Another researcher who has helped take the technology to a new level is Kevin Keegan, DVM, MS, Dipl. ACVS, associate professor of veterinary medicine and surgery at the University of Missouri. He has pioneered development of a wireless method for recording and analyzing equine movement with the use of inertial sensors.
We'll hear from both of them as they describe progress in the gait analysis field and report on the ways veterinary medicine is using the latest technological advances. Before we do that, however, it would be well to allow Clayton to take us on a little journey through time to chronicle just how these many advances have come about.
In the Beginning
The "journey" begins well before the Swedish researchers began their landmark studies. A man named Leland Stanford, better known as a railroad magnate and the founder of Stanford University in California, also was a racing enthusiast who owned a world record-holding trotting horse named Occident.
Stanford, Clayton tells us, believed that there was an aerial phase to the trot. He hired Eadweard James Muybridge, a landscape photographer, who proved Stanford's point in 1877.
Up to that time, photographic techniques required lengthy exposure times and produced blurry images of moving objects. It had long been acknowledged that the equine limbs moved faster than the human eye could decipher, but there was little in the way of photographic equipment that could do much better.
Muybridge developed photographic plates with faster exposure times, and as a result, presented Stanford with a rather blurry image of Occident in the airborne phase of the trot. Muybridge expanded his work, taking tens of thousands of sequential still photographs of people and animals engaged in various tasks and gaits.
Next came one of his contemporaries, Etienne-Jules Marey, who developed a photographic gun in which the film actually revolved to record a series of pictures. This, Clayton tells us, was the precursor of the cine-camera, which would receive its greatest usage in the motion picture industry. Soon, there was high-speed cinematography and short exposure times that allowed collection of high-quality scientific films that could be analyzed to study gaits and locomotion. But, Clayton says, high-speed cameras were finicky to use, and there was considerable lag time between making the recording and viewing the results. Some of the time element problems were solved with the arrival of videography and the resultant videotapes.
Clayton describes how computers changed the scene: "Analysis of cine-films and videotapes was tedious in the early years, since the process was entirely manual. Computerization has facilitated this process, and today, fully automated systems are available. The motion analysis system at the McPhail Center (at Michigan State) tracks reflective markers on the subject using eight infrared cameras. The cameras are strobed and can be set to record from 60 to 2,000 frames per second. The markers are tracked in three-dimensional space in real time.
"A computer-generated stick figure is produced that can be rotated and zoomed to give a detailed view of the motion from any perspective," Clayton continues. "Interestingly, the primary market for these systems is now the entertainment industry, where they are used in computer animations and video games. With regard to motion analysis, computerization has enabled us to gather vast amounts of data in a short space of time and to perform computational tasks that would have been impossible only a few years ago."
Progress in the gait analysis field received a major boost in the late 1960s and early 1970s, when Swedish researchers led the way in the use of high-speed cinematography to analyze gaits, especially in trotting Standardbreds. The group also pioneered the use of the treadmill, and soon the combination of high-speed cinematography and the treadmill was providing valuable information about how the horse moved. Additional research involving horses on the treadmill yielded data on the horse's breathing patterns during exercise, and it allowed researchers to accurately measure both respiration and heart rate.
Gait analysis spread to other equine research institutions throughout the world. The range of techniques has expanded to include analysis of ground reaction forces using a large force plate, Clayton says, and still other techniques such as electromyography (which measures muscle activation by nerve stimulation, in order to evaluate muscle coordination patterns) and accelerometery (which measures acceleration or vibrations) are becoming almost commonplace.
At least some of the progress through the years is attributable to research efforts of Clayton and her colleagues. Some of her early work was done at the University of Saskatchewan, where she served for 15 years as a professor of veterinary anatomy. In July 1997, she returned to Michigan State University, where she previously had a brief tenure as a visiting assistant professor. At Michigan State, Clayton was appointed as the first incumbent of the Mary Anne McPhail Dressage Chair in Equine Sports Medicine. A native of England, Clayton grew up competing in eventing, show jumping, and dressage. She is a certified equestrian coach in both the United Kingdom and in Canada.
The Mary Anne McPhail Equine Performance Center opened on Michigan State's campus in 2000. It is a state-of-the-art center for equine locomotion analysis. It is equipped with a real-time motion analysis system, a 60- by 120-centimeter force plate, a telemetered electromyography system, an electronic saddle pressure mat, and accelerometers and transducers customized to specific applications, such as measuring rein tension during riding.
One of the center's prime features, Clayton believes, is the force plate that is located in a long runway. As the horse crosses the force plate, most often at the trot, the force transmitted when the hoof strikes the surface is measured, recorded, and analyzed.
The key to success with the force plate, she says, is to install one that has appropriate dimensions to record a hit by a single hoof at a time, and is large enough that horses are not tempted to step around it. A number of research institutions, she says, have installed force plates, but only one, the University of Zurich, has a force place integrated into a treadmill.
(The force plate at the McPhail Center is installed in a concrete pit below the surface of the runway. The runway and the force plate are covered with a rubberized material, so there is no change in surface texture when the horse crosses the plate.)
Data from the force plate is combined with data from the high-speed cameras to provide a complete analytical picture of the horse in motion.
An area of research in which the sophisticated equipment at the McPhail Center has been utilized involves the study of the equine hock.
"We have performed a series of studies," Clayton says, "designed to characterize the motion of the tarsus (hock) in three dimensions, to determine how much of the motion is occurring at the distal (lower) joints, and to evaluate how the motion changes due to lameness."
Here, in Clayton's words, is part of what the researchers learned:
"The 3-D studies showed that during the stance phase (when the hoof is on the ground), the hock flexed through an average of 11 degrees, which was similar to the values found in previous two-dimensional studies. In addition, the cannon bone was abducted (rotated away from the midline) through 3 degrees and internally rotated 1.5 degrees. At the same time, the cannon bone slid forward and sideways relative to the tibia (the bone above the hock joints that underlies the gaskin).
"During the swing phase of the stride (when the hoof is swinging forward), the hock joint underwent a considerably larger range of motion than during the stance phase," she continued. "It flexed through 45 degrees, abducted through 10 degrees, and externally rotated through 5 degrees. At the same time, the cannon slid forward and sideways relative to the tibia."
There was a great deal more involved in the research than what was succinctly summed up in Clayton's comments, but one of the practical findings can help veterinarians predict what horses are at risk for bone spavin.
"We studied the mechanical effects of synovitis (inflammation of the joint lining) of the distal joints of the hock, which may precede the development of bone spavin (degenerative arthritis of the hock's lower joints)," Clayton said. "Horses with synovitis showed a significant decrease in range of tarsal flexion, and in the amount of forward sliding of the cannon bone relative to the tibia during stance. The reduced sliding motion might result in repetitive loading on a focal area of articular cartilage, which may lead to the development of osteoarthritis."
All of the above raise additional questions. For example, what role does shoeing play in maintaining hock soundness? Do certain types of shoes become a causative factor, or can appropriate shoes help prevent potential problems? The research answered many questions, but, at the same time, raised more.
Clayton and her colleagues also are studying the knee (carpus), fetlock, pastern, and coffin joints in an effort to better understand the ranges of motion and coordination between different joints in relation to preserving the animal's good health and soundness.
From Lab to Field
To date, much of the research and resultant findings on gait analysis have been confined to research institutions. One of the challenges is to find ways in which the technology can be transferred to the veterinarian in the field. It simply isn't practical for the average equine veterinarian to own his or her own treadmill.
Keegan believes that he and colleagues at the University of Missouri might have found a way to incorporate the latest in gait analysis technology into the average equine veterinarian's repertoire. He describes it as a system that requires only a few minutes of preparation time, but it yields results that are as accurate as those obtained when using the treadmill and high-speed photography.
It works something like this, according to Keegan: Battery-powered tranducers, slightly smaller than a matchbook and weighing only a few grams, are attached in four spots on the horse's body--one at the poll, one at the point of the croup or pelvis, one on the right front leg, and one on the right rear leg. The transducers at the poll and croup are attached with adhesive and Velcro, while those on the legs are secured with a leg wrap, to cut down on vibration and to make sure they stay in place.
The horse is then moved out at the trot. This can be done on a longe line or while trotted in a straight line. The transducers have a range of about 300 yards. Because they weigh 25 grams at most, they do not effect the horse's way of going, even though two of them are attached to legs.
The transducers actually are accelerometers and gyroscopes that measure acceleration and angular velocity during each stride. This information is then transmitted to a receiver on a laptop computer containing software programmed to record and analyze precisely what is happening at each phase of the stride. A key advantage, Keegan says, is that wireless technology is involved, meaning that no wires or cables are needed to record or transmit the information.
Signals at the rate of 200 per second are recorded and transmitted by the tiny transducers and, when analyzed by computer, pinpoint which leg is affected and when during the stride peak pain occurs.
Much of the research using this method has been completed at the University of Missouri, Keegan says, and the next step is to move into the commercial field, so the units can be made available to equine veterinarians. At the moment, only two units exist, he says, and both are handmade. The University of Missouri holds licensing rights to the equipment, but efforts are being made to form a private company for manufacturing and marketing.
Great progress has been made in a short time in the field of gait analysis. Perhaps the most exciting aspect is that the stage is set for continued and accelerated progress in the future.
About the Author
Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.