or what is DGA?
Diagnostic Gait Analysis (DGA) combines critical gait evaluation with state of the art musculoskeletal ultrasonography. The exam begins by watching a horse at the walk and trot on an equine treadmill for any deviation from normal gait parameters or sound biomechanics. The horse is evaluated for signs of tension, pain, abnormal load, limb flight and range of motion. This is followed by a comprehensive ultrasound in order to reach diagnoses and guide treatment.
On the treadmill, we often identify several problem areas and are able to estimate the clinical significance of each – these are our clues. Depending on the manifestation, these clues may be very specific or more generalized. For instance, we can often localize joint pain to specific joints while other clues may point us to regions such as the distal limb. Similarly, areas of muscle tension are easily appreciated on the treadmill, which might indicate long term compensation or a primary muscle lesion. This is the first part of DGA.
The second part of DGA is about digging a little deeper. If the treadmill reveals clues, then ultrasounding is a hunt. The techniques used have been optimized across two decades to improve specificity and efficiency, in turn maximizing diagnostic capability. Using these techniques, we are able to evaluate all gross biomechanical units – from the TMJ and shoulder down the front legs to the spine, sacroiliac, and hip down the back legs – from bone surface to muscle, soft tissue and synovial structures including cartilage, synovium, villi and capsule.
In other words, if there is lameness, there must be a source. The treadmill reveals the lameness while the ultrasound uncovers the source. This symbiosis, allowing the confirmation of clinical suspicions with specific diagnoses, is the foundation of DGA.
But sometimes the easiest way to explain a thing is to describe what it is not. Similarly, it may be easiest to understand DGA by comparing it to traditional flexion tests and nerve blocks. So for this next section, I’ll try to explain DGA against, perhaps, a more familiar backdrop.
The purpose of a flexion test is to isolate and exacerbate a pain response. I use isolate loosely because flexion tests are actually very non specific. You are only able to “isolate” a lower limb or upper limb, but not specific joints or structures. The idea is to apply controlled stress on certain joints and evaluate the horse’s response. If the horse appears more lame after flexion, the flexion is considered positive.
Nerve blocks work the opposite way. Numbing solution is injected around target nerves or in specific synovial structures in an attempt to eliminate lameness. Nerve blocks are characterized in percent resolution and are considered successful if they decrease the degree of lameness above a certain predetermined percent.
Now in this next section, I am in no way attempting to discredit the value of flexions and nerve blocks, but there are pitfalls to any system. Instead, my purpose here is to compare two different approaches in order to highlight some advantages of DGA – namely, greater objectivity, precision, sensitivity and efficiency.
So here we go.
1. Objectivity. Consider the many factors that influence a flexion test – a horse’s pain tolerance, the amount of force applied during each flexion, the amount of time each flexion is held and variable environmental factors such as distractions, footing, handler speed and so on. Conversely, the treadmill allows the horse to move freely in whatever manner is most comfortable while providing a stable point of perspective for the clinician. In this way, the horse reveals the lameness without external influences and the observer is allowed to detect all the nuances of gait alteration without fear of over interpreting confounding or circumstantial information.
“DGA is like listening to music on a really high end system because this system doesn’t add or subtract anything from the original recording. It just plays what is there.” -Doctor Per
The treadmill exam is very standardized. The horse is evaluated in the same environment, at the same speed, on the same surface from exam to exam and season to season. Now obviously if you have a three legged horse this attention to detail is not necessary. But when you are trying to decipher the cause of decreased propulsion, increased resistance during certain exercises or simply decreased performance, you want the best most detailed information possible. What I mean is, if you are a secret agent trying to crack a really tough code, you need as much of the key as possible.
“Flexing and blocking is like studying teeth while DGA unlocks the smile.” -Doctor Per
2. Precision. I have already alluded to the inherent lack of precision in flexion tests, and the same holds true for nerve blocks. The problem is, you do not always know where the numbing solution goes after injection. There have been a lot of studies using contrast in the solution that proves it can move around quite a lot under the skin, and not always in the predicted way. This means that we do not always know what we are numbing, and often when we are trying to block just one thing, we wind up blocking other things as well.
“Lameness is multifaceted, like daylight. The sun rises exactly the same way every morning, but despite this, every sunrise is different. It’s the same with lameness. Even though two horses may present the same (say stifle pain), the cause could be joint inflammation, muscle strain, cartilage damage or ligamentous injury. The DGA will reveal all of this.” -Doctor Per
3. Sensitivity. In the medical world, sensitivity specifically means how well a certain test accurately identifies certain syndromes. In other words, if you lined up ten sick men, a test with high sensitivity would correctly identify all ten sick men while a test with low sensitivity would find only the 7 most obviously sick.
So in regards to lameness, sensitivity means how good we are at detecting subtle changes in gait that could indicate a problem. The reason this is so important is because, barring catastrophic injury, big problems start off as little problems. If we get good at catching and treating the little problems, then maybe we never have to treat the big problems. If we can catch and treat a chronic synovitis before the inflammatory cycle degenerates into osteoarthritis, we can prevent new bone formation and cartilage loss. This improves prognosis and extends a horse’s athletic career.
“Flexing and blocking is like sailing when there is a lot of wind, but it is much harder to sail without much wind. DGA is like sailing in less wind. If you train your eye, you can see all of the details of low grade lameness. This is important because the low grade lameness is often the root of the problem. The secondary lameness sites are more obvious and easier to find, but if you only treat these, the problem soon reappears – or worse, you find there is not much improvement after treatment. To get a big improvement, the primary lameness must be found and treated. The primary site is often high up on the horse (stifle, hip, sacroiliac, etc) and these sites are the hardest to find by flexing and blocking.” -Doctor Per
4. Efficiency. Before DGA, flexing and blocking was the most efficient way to make sense of a lame horse. But a lot has changed since then. With modern accessibility to medical imaging, we need a new standard of care. And with the use of ultrasound in particular, we no longer have to sacrifice detail for efficiency. Instead, we gain a great deal of detail without having to wait for nerve blocks or flexion test redundancy.
In close, I would like to leave you with one important, final thought. Let’s call it the icing on the cake. And let’s face it, a cake is not a cake without icing – which is exactly the point I want to make. That is, DGA is kind of like baking. If you are making a cake but forget any one ingredient, then your cake is not going to taste very good. It might be edible, but then again, it might not. The lame horse works the same way. So long as you remember most of the ingredients, you might get something you can eat, but you have to remember all of them to get a really tasty cake – or a really sound horse. And do not forget that, although all ingredients play a role, sometimes it is the smallest, most insignificant seeming part that makes the biggest difference (like adding a little vanilla or cinnamon spice).
Or think of wine, to put it another way. Wine is 80% water and 10-18% alcohol, tannic acid, malic acid, sugar and tartrate etc. But it is the 2-3% diffused aromatic gases that gives wine 100% of its flavor. Similarly, leave 2-3% of a lameness untreated, especially if that percent is a primary site, then even after treating 98% you are not going to be satisfied with the result.
I mentioned a symbiosis between the treadmill and ultrasound earlier, but I should have just as easily called it synergy, because when you treat the whole system, the sum effect out-performs any individual part. By providing a framework for a thorough initial evaluation, DGA starts with the big picture, then dissects down from there – that way we do not miss the forest for the trees.
And speaking of forests, “thats all I have to say, about that.” -Forest Gump
“So is DGA the perfect solution for understanding why a horse doesn’t perform? No, perfection is not in the equipment or a particular system. Perfection comes from somewhere else. But while we may never reach perfection, we can get a whole lot closer with the help of a system like DGA. And remember, soundness is like fresh milk. Enjoy it while it lasts.” -Doctor Per