RESPONSE TO LAMENESS LOCATOR QUESTIONS
Ok, so I, along with my engineering colleagues, are the developers of this inertial sensor system, now called Lameness Locator. All of your comments are valid and interesting. I have taken the liberty of responding to some of your comments. I hope that this is OK.
<<My only complaint/criticism about the device is that one of the sensors is placed on the right front foot. However, when I asked the vet if maybe my horse was setting off the sensor by moving differently in that right front because the device is wrapped around his pastern - the vet dismissed the possibility.>>
This is a common and understandable question by clients of veterinarians using the device. The sensor on the right forelimb is a gyroscope. It is used only as an indicator of when the right front limb is on the ground and when it is in the air. All of the lameness evaluation comes from the signals of the accelerometers on the horse’s head and pelvis, in other words calculation of lameness severity is entirely dependent on the acceleration up and down of the torso and has nothing to do with the limbs. There is no reason to think or believe that putting a wrap on the limb will cause the torso to move up and down any more or less. In fact, we have tested this fully and putting wraps or small weights on the limbs does not appreciably affect torso vertical acceleration and deceleration. It is possible that very heavy weights placed on the limb, such that the horse has to work to lift the limb, could affect torso acceleration but the sensors used in the system weigh only 28 grams, which is inconsequential. I guess it is possible that if you really wrap the limb tight, for example so tight as to constrict blood supply, that it can cause pain and this would in turn cause lameness, but the pastern wrap that holds the sensor on the right front limb does not have to be wrapped very tight.
<<What started out as a lameness exam for $150 turned into a $500 vet bill after all the other tests were done to try to pin-point the lameness because the device had me worried that there was something seriously wrong. My horse was mostly sound, but exhibiting some unevenness in his collected dressage work so I assumed it was his hocks (which he has had issues with in the past), but the sensors did not detect lameness in the hind.>>
Unfortunately it is the mild lameness problems, that nevertheless adversely affects the horse’s performance, that are the most difficult to pin down. I have been developing and using this system for many years now and if the horse has any asymmetry in hind quarter torso acceleration, and I have no doubt that the system will pick it up. I would have to know more about why the equipment did not pick up a lameness in the hind limbs of your horse. Here are the possibilities in order of likeliness. 1) The horse actually did not have a hind limb lameness. 2) the horse has mild bilateral hind limb lameness that was “exactly” equivalent in both hind limbs. Other manipulations, like flexion tests, may help to “bring out” the lameness. The equipment, by the way, can be used to measure the effect of flexion tests.
<<NC State took training from the developer of the system, wonder if your vet might have problems with the settings? The problem with technology is that it is only as good as the person operating it! But I am no vet…>>
NC State, Dr. Michael Schramme specifically, has been using this equipment now for almost 2 years. He is, I think, very good at analyzing the data. There is some training that is needed so that the veterinarian can get the most out of its use. Almost everyone that has the system now has either had personal face-to-face training or an in-depth, on-line training. There are only a few that have not yet done this. The training is not in lameness evaluation, which is not needed because most of the current users of this equipment could teach me a thing or two about lameness, but only in interpreting the analysis.
<<I also wonder if this type of equipment is more suited to significant lameness, localized to one leg. It would make sense, finer level of lameness hard to register, multi leg–confounding data. Also, if equally sore in hind legs, it would counter the numbers I would think…>>
I disagree. It is most beneficial for horses with mild lameness or in horses with apparent multiple limb lameness. It is designed for these types of cases. However, we now use it on every horse that comes in for lameness evaluation, for 3 reasons. 1) When you see the results on horses with easy lameness or in sound horses you rapidly gain more in-depth understanding of the analysis results, especially when using on horses while lunging and after flexion tests. 2) Sometimes what looks like an easy lameness in the beginning turns out (after blocking) not to be so easy and we wish we would have had the pre-blocking baseline against which to compare. 3) It takes too much time to run back into the clinic to get the equipment after we first decide that it is a case where it might be useful. The students and technicians in our practice are trained to “instrument” the horse right away. It takes only 3 minutes. Sometimes they are so fast that I may not even had time to palpate the horse first (something I always like to do first) and I have to remove the pelvic sensor because it gets in the way of my complete lameness palpation. I highly recommend to those who are using the system to, at least during the beginning weeks of use, put in on every lameness, pre-purchase, and “not performing right” case they evaluate.
It is theoretically possible for horses with bilateral lameness to be exactly equivalent in pain of lameness on every stride, but this in reality almost never happens. Navicular disease (for forelimb lameness) and distal tarsal arthritis (for hind limb lameness) are the most common culprits. However, for both these conditions and others that are frequently bilateral, the most common situation is one side is a little worse than the other. So, for example a horse with an average grade 3 lameness in the right front and an average grade 2 lameness in the left front will be measured as an average grade 1 lameness in the right front. This is a limitation of any objective method of lameness evaluation that evaluates asymmetry as a measure of lameness. Another situation that is much more common than a bilateral lameness that is exactly equivalent one side versus the other on every stride, is a bilateral lameness in which the lameness switches sides, back and forth sometimes several times during the same evaluation. In this case the thresholds between soundness and lameness may not be reached for each limb. However, this will be displayed in the plots provided and this is perhaps when having more experience with analysis of results may be important. Also, for horses with bilateral lameness, veterinarians utilize other evaluations (other than just evaluating the horse trotting back and forth) like lunging and flexion tests to help “bring out” the lameness, one side compared to the other.
<<if my horse had improved with each nerve block I might have been much more convinced that it was his front right, but even after blocking everything from the knee down, he was still registering 0.446 (0 is the threshold.)
His hocks, however, which we know he has issues with - OCD, surgery, arthritis, etc. - only registered .152 which is only slightly above threshold and the vet said those numbers probably indicate stiffness and not lameness.>>
There are actually more than one value reported to the veterinarian that they should take into account when evaluating the results and not just the threshold value that you allude to. A horse can be lame when it is under the threshold if the variability in asymmetry is quite low (a very mild but consistent lameness) and the horse can be sound when it is over the threshold if the variability in asymmetry is quite high (data too variable to make a valid conclusion). There is by the way no threshold reported by the system that is normally “0”. I am pretty sure that your vet using the equipment understands this and it may have just been communicated in this fashion as a simplification.
<<Yeah, if the vets had walked out and said, ‘this instrument is going to decide whether or not your horse is lame and needs surgery’, I would never have gone for it.>>
I hope this never happens and I doubt that any current users would do this.
<<I wonder how the device deals with acceleration asymmetry in the horse’s gait due to limb length disparity or high/lo hoof pairs.>>
This is an excellent observation and one that we have also thought about a few years back. We have tested this experimentally by artificially creating limb length and hoof angle asymmetry in both forelimb and hind limbs. It turns out that induced limb length asymmetry or hoof angle asymmetry in the front limbs has no to very little effect on torso vertical movement asymmetry in the short or long term. It seems that the soft tissue sling connecting the limb to the vertebral column dampens this effect. Induced limb length or hoof angle asymmetry in the hind limbs will affect results, but only in the short term (hours to days). After a few days of induced limb length or hoof angle asymmetry the effect on vertical torso acceleration is not measurable. I do not know exactly how the horse does this, but it does.
<<but it’s not meant to replace an experienced practitioner by any means.>>
Absolutely. It is not meant to and in fact cannot replace the experienced practitioner. Equine veterinarians and anyone else who knows much about lameness knows this. It is only a very sensitive aid.
<<We did have one set of results that we questioned turn out to be due to the fact that one of the sensors was a bit loose and moving a little on its own though…it kind of created a ‘back ground’ noise>>
The gyro data on the right front limb is remarkably resistant to “noise” created by jiggling in the pastern wrap. We filter the gyro signal. It can however, cause erroneous results if it rotates on the limb. If it rotates 90 degrees to the side of the limb you may not actually get any results. If it rotates all the way to the back of the limb you will get “opposite-of-true” results. The algorithms (a fancy word for “rules” or “equations”) depend on the gyro being positioned on the front part of the right forelimb. Putting them on any other limb will give erroneous results.
<<Or the vet I know of who kept saying one leg was lame when that foot had an egg bar on it and the other foot did not.
All can say is there is no substitute for well trained eyes and ears (oh wait…those are lots cheaper)>>
Limb length asymmetry, especially as small as that cause by a shoe on one foot, will not affect results. See above comments. There definitely is no substitute for well trained eyes and ears. Well trained eyes and ears do much more than evaluate the motion of the horse. Well trained eyes and ears evaluate the entire horse.
<<There is a HUGE presumption that asymmetry of amplitude = pain. No “baseline control” mechanism to rule out other factors which can and do cause asymmetry in amplitude. I didn’t even think about that. That could be a very valid threat to the reliability of the test.>>
This was, indeed, a huge presumption early on in development. However, disregarding foals and yearlings (young horses in general), which sometimes show dramatic “handedness” or natural asymmetry, it turns out that horses trotting in straight lines have remarkably symmetric vertical torso acceleration and deceleration when they are sound even when their limb movement is quite asymmetric. The same cannot be said about lunging. I am not saying that there are no horses out there that are sound but display significant asymmetry in vertical torso acceleration but they are uncommon.
<<I’m curious how a sensor on one leg could detect lameness in all four? I could understand if there was a sensor on each leg, but it seems a little weird to me with only one.>>
The gyro sensor has to be put on the right forelimb. The algorithms depend on this. The gyro sensor does not detect lameness. The gyro sensor just indicates when the right forelimb is on the ground and when it is in the air. All other limb placement can be approximated (which is all that has to be accomplished for the algorithms to function correctly) if the gait is known. If you put the gyro sensor on the left front limb it will give “opposite-of-true” results. I do not really know what would happen if your put the gyro sensor on the hind limbs. Probably it would give correct results if you put it on the left hind limb and “opposite-of-true” results if you put it on the right hind limb, but I have not done this specifically.
<<The MARKETING is aimed at folks who aren’t engineers.>>
Actually right now there has been no real marketing to date, just word of mouth. When it is marketed it will be marketed only to equine veterinarians.
Kevin Keegan DVM, MS
Diplomate ACVS
Professor: Equine Surgery
University of Missouri
Columbia, MO 65211
