Out of the gait

Dr. H. was asked to be an event veterinarian for the American Endurance Riding Championships. Out of school for more than 10 years now, Dr. H. considered himself gaining in experience but still learning. When it came time to judge the gaits and motion of the top-10 finishers for the Best Conditioned Award, Dr. H. was excited to hear that all eight veterinarians working the event were going to view the horses in motion and then, as a group, the veterinary staff would pick a consensus winner. There were at least four veterinarians at this ride who were legends in the sport and who had at least 100 years of combined experience evaluating sport horses and analyzing gaits.

A veterinarian (middle) watches a competitor's horse trot 125 feet out and back and then must determine if the horse is lame or is fit enough to continue with the ride. In a typical 50-mile ride, horses are examined four to five times; with upwards of 75 to 100 horses in some rides, this affords the veterinarian many chances to improve the fine art of gait evaluation. Note that the man in overalls is recording the trot out, which the rider will later review and evaluate for possible tips to improve future performance.

"This is my chance to really learn how experienced veterinarians dissect equine gaits and improve my own attempts at lameness diagnosis. I'll make my evaluation and then see how I compare to what my mentors say and what I need to do to improve my eye and evaluation techniques," the young doctor thought.

The top-10 horses were brought out, and they trotted in a figure eight for all the veterinary judges who then went to a separate room to talk about the evaluation.

Dr. H. was not prepared for what happened next. There was no sense of agreement between the vets at all. One veterinarian's best moving horse was another's worst mover. The same horse was judged to have good impulsion by one vet and poor impulsion by another. The more experienced veterinarians were more forceful in their opinions and had better reasoning behind their interpretations of motion but had no better agreement than did any of the less experienced veterinarians. As the sometimes-heated discussion raged on, Dr. H. began wondering how accurate gait evaluation really was if it could be this subjective at this elite level.

And Dr. H. is not the only one. Dr. Kevin Keegan, a veterinarian in the E. Paige Laurie Endowed Program in equine lameness at the University Of Missouri College Of Veterinary Medicine, is one of many researchers who have been looking at this problem. Keegan recently presented papers on the head and pelvic motion patterns of horses with either fore or hind limb lameness. These presentations at the 2005 American Association of Equine Practitioners meeting in Seattle discussed the actual motion of horses with specific lameness issues and called into serious question much of what we think we know about lameness and motion in the horse.

Keegan and other researchers represent the field of kinesiology, or the study of the forces that are involved in movement (kinetics). The development of high-speed film and computer-aided motion analysis has allowed this field of study to expand and subsequently question the efficacy of current standard practices and suggest how veterinary students should be taught to evaluate equine gait and motion.

Out of plain sight

The human eye cannot distinguish events occurring in less than a tenth of a second. At full gallop, a horse takes upwards of 150 steps per minute. At 2.5 steps per second, there are undoubtedly some parts of body, leg, joint and foot motion that humans cannot see. Even at slower speeds in different disciplines many parts of a horse's motion are not observable, and if other factors such as jumping and landing motion or other specific movements dictated by a particular sport are thrown in, then it is no stretch to say that parts of a horse's motion are being, and have always been, missed on evaluation.

New equipment in use at the University of Melbourne Equine Center in Australia and elsewhere now can record a horse's motion at 500 frames per second. Even a standard digital camera will record 30 frames per second. Therefore we now have the ability to simply see things that could not be seen before.

In his papers, Keegan reviews the time-honored standard description of fore-limb lameness as he quotes Dr. O. R. Adams: "As a result of lameness in a fore limb, the head will drop when the sound foot lands and rise when weight is placed on the unsound foot or limb."

This "head bob" or "down on sound" approach was the standard for veterinarians for many years, and the same could be said about the idea of a "hip hike" for hind-limb lameness.

But new high-speed gait analysis shows that fore-or hind-limb motion follows a much more complex pattern, and it is the human eye that seeks to simplify this motion.

Keegan says it is important to differentiate between a lameness that shows that the head moves down during the loading phase of the gait, but the absolute height is higher than during the stance phase of the sound limb and a lameness where the head never moves down to a lower position during stance phase of the lame limb compared to the sound limb, for example. Both of these horses will appear to drop their heads when placing weight on the sound limb, but the subtleties of motion can, with the help of high-speed film and computer programming, be better evaluated so a lameness due to a problem in a carpal joint can be distinguished from a lameness involving the flexor tendons of the foreleg. Currently there is little use of these subtle variations in gait analysis, and most clinicians simply first try to determine "right or left limb and fore or hind," says Dr. Bill Moyer, head of veterinary large animal and surgery at Texas A&M. "Clinically that is where you start: Identify the leg, then the site, then work up the lameness."

Though the clinical situation is reversed (veterinarians are given the task of uncovering where the horse is lame), it is important that anyone trying to learn to evaluate lameness should know exactly where the horse is lame before looking at the horse.

"You can look at 100 horses, and you will certainly cement in your mind some idea of characteristics to use for an evaluation of gait, but you also may be wrong," Keegan says. "Your diagnosis of the site and possible cause of the lameness may be incorrect, so the gait abnormalities you learn to correlate with a particular lameness — the dropped shoulder, the decrease in stride length, the difference in hoof height — may be confusing to flat out incorrect. Repeating those observations 100 times only makes it more likely that those deviations in motion become a standard part of how you diagnose. But it does not necessarily make you better at it if your initial evaluation is wrong."

By knowing the source of the lameness first, a veterinarian or a student then can look for patterns of movement that would help correlate between specific gaits and motion and the correct underlying lameness cause. The cause in this case need not be the final end diagnosis but gait evaluation techniques still will be improved if certain gait characteristics can be linked to regional diagnosis, such as pain in the foot, a problem in lower-limb tendons and ligaments or a particular joint area for example.

To this end, there are thousands of gait analysis tapes available to the students at the University of Missouri College of Veterinary Medicine. Students can access these tapes and can view side-by-side comparisons of lame and sound horses. This repetitive viewing "accelerates the skill accusation for evaluating lameness," Keegan says, and it equalizes lameness evaluation because it reinforces that all veterinarians should be looking for the same markers as clues to specific lameness.

Though film always has been an important tool for gait analysis, modern technology allows practitioners to take a closer look at the details.

"When I started out in 1969, my first 'big' purchase was not a new truck but a 35-mm camera, and I've gone through 10-15 different cameras since then" Moyer says.

He likes to take a closer look for two reasons: "Either the horse's motion is so strange and unique that you've never seen it before and need to record it, or the motion is a classic example of a horse with a particular condition."

Practice makes perfect

By consistently filming and reviewing all of the odd cases, practitioners can begin to classify them. The best way to learn to evaluate gait and diagnose lameness, sources say, is by exposing yourself to as many horses in motion as possible. The more you see, the better you learn, especially students and young doctors.

It's beneficial to have some seasoned diagnosticians around the study circle, as well as a few trainers, farriers and other horsemen, too, Moyer says.

Keegan's approach is slightly different: He would have students watch film where kinematic gait analysis becomes the "experienced clinician" by showing them why the horse moves abnormally (or normally). It teaches them what to look for.

Many other standard lameness teaching courses or clinical rotations depend on the luck of the draw for exposure to lameness cases. The vast majority of lameness cases never make it to a veterinary school because those horses are successfully treated by field veterinarians or improve on their own, Moyer says. It is often difficult to find ample cases of lame horses for students to learn from. Gait analysis and film review helps reduce this problem, though experienced clinicians caution that looking at film in a study session does not accurately duplicate the experience of evaluating a horse in the field on a windy day in cold conditions or at a horse show with variables in surroundings, footing, handling, lighting, distractions and so forth. Kinematic gait analysis and study is a wonderful tool, but it is still important to get out there and watch horses move in the actual situations where you will be required to diagnose them.

There is another benefit to high-speed gait analysis. Remember Dr. H. and the Endurance Championships? The issue of subjectivity in lameness evaluation is an important one. Veterinarians are called upon to evaluate gait, motion and impulsion for any number of reasons and in many situations. Horses are bought or sold; therapies and treatments are accepted or rejected all because of a veterinarian's subjective evaluation of gait. Does this horse move well? Should it be recommended as sound for purchase? Is this horse's gait better after a palmar digital nerve block or not? Does it have a problem in the foot or not? If I give this drug or medication to this horse, does it significantly improve its gait or motion? These questions all require an evaluation of gait and many times that evaluation becomes subjective.

"Just what is a hip hike? How high does it go and what actually hikes?" Keegan asks. "Anatomically we know that this almost never happens in mild to moderate lameness. And what about impulsion? What exactly do we look for, what motion or parameters are being observed to arrive at a non-subjective idea of impulsion?"

Data points

Each veterinarian makes his or her own determination, and there appears to be little consistency or science behind many of those interpretations.

To try to understand the subjective aspect of clinical gait analysis and to try to make a stronger case for kinematic gait analysis, Keegan and colleagues did a study investigating how veterinarians evaluate known lame and sound horses. Six equine clinicians, five residents and two interns representing three veterinary teaching hospitals, 19 horses with known lameness and five normal, sound horses were used. The horses were trotted on a treadmill and subjected to high-speed video and computer-assisted kinematic gait analysis. The treadmill sessions were filmed; some horses were administered particular nerve blocks and re-filmed. A total of 80 sequences then were randomly copied onto a tape; 20 of the original 80 sequences were selected randomly and then randomly recopied onto the first tape. This created a number of views of lame horses, sound horses, and at least 20 sequences that were duplicates so Keegan could look at the sensitivity of gait evaluation (did they see what was actually there?), the accuracy of diagnosis (since the actual lameness was known), the accuracy of detection of a change in lameness following nerve blocks, and the consistency of evaluation (did they evaluate the repeated 20 horse sequences the same since they would have no way of knowing that they were repeats of film they had already seen?). The results shed some light on the apparent variability in gait analysis among even experienced clinicians.

More experienced clinicians were more repeatable in their evaluations. The same horses were judged to be sound or lame, and the site of the lameness remained consistent from sequence to sequence. Less-experienced residents and interns did not stay as consistent.

"Clinicians as a whole were not any more reliable at identifying the true degree of lameness than interns or residents," Keegan says. "This was a disappointing finding because it did not indicate a transference of a uniform knowledge base in the training programs involved in this study."

To be fair to the participants, only one side view of each trotting horse was taken and no sound was available. All practitioners realize that watching a horse move from various angles and often listening to its footfalls and cadence can impart a tremendous amount of information that helps with gait evaluation.

Keegan's study also found poor correlation between changes in kinematic variables and the clinician's subjective score for lameness improvement in horses that had received nerve blocks. Essentially the camera and computers had registered changes in gaits following nerve blocks that the veterinarians did not, and clinicians did not focus on irregularities of motion in their evaluations.

Two major concerns developed following the study.

"It is important to investigate the reasons for disagreement between clinicians so that we can improve our ability to correctly describe lameness to veterinarians in specialty training programs," Keegan asserts.

It is difficult to teach lameness evaluation if the teachers do not agree. Even though cameras and computer analysis identified very subtle changes in gait, the temporal and spatial resolution of the human eye probably precluded the use of these subtle gait variables (increased fetlock extension during stance of stride, decreased total vertical head excursion and a long list of other limb and body motions) in the clinical detection of lameness and certainly in the process of teaching gait analysis to veterinary students and clinicians.

Computer-assisted gait analysis may be a developing diagnostic lameness tool when used to its capacity, but it must be simplified and used for comparison and repetition when employed as a teaching aid.

So although some refinement is needed to make high-speed gait analysis a more practical modality, researchers, educators and practitioners all agree on a few points:

• Learning to evaluate equine gaits and diagnose lameness remains one of the biggest challenges for veterinarians and it is, and should be, a career long process of improvement.

• High-speed photography allows veterinarians to "see" what they cannot, and advances in gait analysis kinesiology will allow veterinarians to correlate gait changes to specific pathology and eventual diagnosis.

• Students being taught with these newer methods are only now becoming practitioners, and it remains to be seen if they will improve the profession's accuracy, sensitivity and consistency when it comes to gait evaluation and lameness diagnosis.