Lameness Locator does not agree with my subjective interpretation

Don’t get intimidated.  This is something that I have run into many times, mostly with veterinarians in the middle of their careers, who are a little sensitive about their skill with lameness diagnosis.  The older, seasoned, more confident ones do not worry about this at all.  They know that there are just some cases where it is difficult.  Being at a University for the later stages of my career has driven this home to me, because you always have another clinician looking over your shoulder.  Sometimes we disagree and sometimes I have to admit I am wrong.  This equipment will sometimes disagree with a skilled clinician.  In the early stages when I disagreed with the equipment I was more prone to think that it was making a mistake.  After using it for many years, and seeing the outcomes of cases, I am now more prone to think that I am just not correct when this happens.   Let’s face it, if this equipment never disagrees with a clinician then he/she is only using it on easy cases, or it is good for nothing.  I have thick skin now.  If we are using it on a case and I say RH but the resident says LH and the equipment says LH, we all just have a little laugh.  I am still the boss.  The client totally understands this and appreciates the extra objectivity.  In my earlier years I was a little more sensitive to this now I do not care at all.

Lameness Locator is your friend not your enemy

I was once told this by a practicing equine veterinarian, "[Lameness Locator] devalues the need/expertise of the veterinarian".  This was my response.

This is something that I have run into many, many times and it is a completely misplaced concern.  In fact I think it is quite sad and depressing.  Anyone who thinks this really knows nothing about Lameness Locator and, in my opinion, is trivializing the role of the veterinarian in diagnosing and treating lameness in the horse.  First of all, Lameness Locator is sold to equine veterinarians only.  It will never, ever, over my dead body, be sold to anyone other than equine veterinarians.  There is good reason for this.  The information provided by Lameness Locator is only helpful to equine veterinarians, anyone else and the information will be useless and potentially abused.  Also, the client knows nothing about the Lameness Locator results, it is just a bunch of squiggly lines to them.  It requires the equine veterinarian to explain it to them.  Does this thinking also apply to radiographs, to ultrasound?  Does taking radiographs devalue the need/expertise of the veterinarian.  Does performing an ultrasound devalue the need/expertise of the veterinarian?  Of course not.  It actually increases the need/experience of the veterinarian.  Without the veterinarian interpreting the results the images are pretty worthless.  Of course you have to be able to interpret the images and if you do not use Lameness Locator you cannot interpret the reports.  There is also much, much more to working up a lameness than picking the correct limb or limbs.  This is just the tip of the iceberg, moments in the time span of a complete lameness evaluation.  Understanding the history, use of horse, limb palpation, blocking, image interpretation, deciding how next to proceed, image interpretations, deciding what imaging to perform, putting all the pieces together, conversing with the owner, finding out what he/she really wants…..This is where the skill, knowledge, expertise, and if I may add, the art, of the equine veterinarian shines through in lameness evaluations.  Pinning the bulk of the perception of the need/experience of the veterinarian on picking the correct limb or limbs is very short-sighted.  In my opinion is it a cheap portrayal of reality. 

Ross and Dyson, "Lameness in the Horse": A study.

You have heard of Bible study.  The line by line dissection of passages searching for spiritual meaning and the literal, or not so literal, interpretation of what the passages really mean.  Everyone would agree that the bible is a must read for the Christian.

Well, for the equine practitioner interested in lameness evaluation, a must read is the chapter in Ross and Dyson’s new “Lameness in the Horse”, which can be thought of as a sort of version of an equine lameness bible.  Although the entire book is excellent, chapter 7, by Dr. Ross, is by itself worth the price of the book.  The chapter is not an easy read, but if read slowly and deliberately, and studied in depth, the reader will find it chock full of pearls of wisdom that are, for the most part, not only obviously Dr. Ross’ professional opinion, which by itself would be adequate, but remarkably consistent with experimental studies.  For those of you currently using Lameness Locator it is definitely a beneficial read. 

http://www.elsevier.ca/ISBN/9781416060697/Diagnosis-and-Management-of-Lameness-in-the-Horse?vm=r

I have read and studied, in depth, this chapter in the latest version of the textbook (as well as in earlier versions) and have reconciled it with published, evidence-based equine veterinary literature as well as with what I have measured in our lameness laboratory and in research and clinical cases using the Lameness Locator system.  In an attempt to make sense of what you have come to expect with Lameness Locator results in light of what is described in this chapter, I will periodically, starting today, take and interpret, giving my own opinion, certain “passages” from this chapter.  Perhaps this will stimulate comments and discussion by others.

The first point I would like to consider, and actually concede, is the difference between Dr. Ross’ definition of compensatory lameness and mine.  Dr. Ross defines compensatory lameness as a true lameness, an actual secondary or complementary lameness, from overloading of limbs due to the primary lameness.  Compensatory lameness, as defined in the Lameness Locator training manual and other training publications, is an apparent, but false lameness, due to load shifting away from the primary lame limb.  Theoretically, this compensatory movement, should be abolished once the primary lameness, for example after a successful block, is abolished.  Long term compensatory load-shifting, however, can develop into a true, i.e., painful, secondary lameness, which of course, would not be immediately abolished after blocking out the original, primary lameness.  This definition of compensatory lameness, as an apparent, but actually false lameness, has always been made clear in the Lameness Locator literature.  But, I would concede that it is probably not semantically appropriate to use the noun “lameness” to describe something that is not really painful.

The Lameness Locator system picks up asymmetric torso movement.  So, it will measure apparent, but false lameness, as a true lameness.   It is up to the user to decide, drawing from his/her knowledge and experience, about compensatory movement patterns and secondary lameness occurrence (studying this chapter will help), what is what.  This is another example of why Lameness Locator, as it is with any medical device, will be useless in the hands of anyone other than an equine veterinarian.

Understanding the difference between an actual compensatory or secondary lameness and compensatory movement that only looks like lameness is paramount to understand the Lameness Locator results as well as to understand much of what is described in Chapter 7 of Ross and Dyson.

For the next blog entry, I will try to describe what Dr. Ross means by this passage, “Moderate-to-severe hindlimb lameness can mimic ipsilateral forelimb lameness….”, which can be found as the last sentence on page 66, in the section entitled, “Determination, Grading, and Characterization of Lameness”.  I will be concentrating on the word “mimic”."

Law of Sides, Why I Use Lameness Locator on Every Case

I had a case the other day that points out 2 things very clearly, 1) the second part of the “Law of Sides” and 2) why I put Lameness Locator on all my lameness cases.

The second part of the “Law of Sides” is the second rule for evaluating compensatory lameness patterns in the other half of the body in horses with primary lameness in one limb.  The first rule, which is not the subject of this post, states that, when a horse is trotting, an apparent ipsilateral lameness, e.g., a right forelimb and a right hind limb lameness, is most likely a primary hind limb lameness with a compensatory, and therefore false, forelimb lameness.  This first part of the “Law of Side” is well known to most equine practitioners, something that happens very often, and is something to definitely watch out for when performing lameness evaluations in horses.  The second part of the “Law of Sides” is, however, most often understood as just the opposite, i.e., an apparent contralateral lameness, e.g., a right forelimb and a left hind limb lameness, that is most likely a primary forelimb lameness with a compensatory, and therefore false, hind limb lameness.  But this second part of the “Law of Sides” is a little less simple that this above explanation implies.  The compensatory pattern of vertical pelvic movement, which is what Lameness Locator uses to detect hind limb lameness, can be one of two different possibilities, or it can be both.  A primary forelimb lameness may cause an apparent compensatory, but false, ipsilateral hind limb impact type lameness, or an apparent compensatory, but false, contralateral hind limb pushoff type lameness, or both.   This pattern of compensatory vertical pelvic movement has been measured experimentally, and the contralateral hind limb pushoff pattern is more common and significant, but both can occur.

Here is an explanation of this observed pattern.  If a horse has a primary forelimb lameness, when it is trotting, it will shift its weight backward slightly during the diagonal stance phase including the affected forelimb.  So, the pelvis will fall more on the contralateral hind limb compared to the ipsilateral hind limb.  This makes it appear like, and with Lameness Locator, measure like, the horse is coming down less hard on the ipsilateral hind limb.  Thus, the ipsilateral hind limb impact type lameness.  However, if the horse is trotting in a straight line, in order to keep going in a straight line, the horse will then push off harder on the opposite diagonal stance phase, the one including the normal forelimb.  So the pelvis will rise more during pushoff of the ipsilateral hind limb.  This makes it appear like the horse is not pushing off so hard on the contralateral hind limb, the one in the same diagonal stance phase as the lame forelimb.  Thus, the contralateral hind limb pushoff type lameness.  Horses with forelimb lameness can display no compensatory vertical pelvic movement pattern, or it can display one of the above mentioned patterns or both.

I have taught the “Law of Sides” to veterinary students for the last several years and I have usually told them that the second part tends not to be a problem, either for subjective evaluation or for using Lameness Locator, because the primary forelimb lameness has to be quite severe before you will actually appreciate the asymmetric vertical pelvic movement.  The following case proves me wrong and reinforces that there are always exceptions to any rule.  It is also a very good example of why it is good to put Lameness Locator on all lameness evaluations, even when it, at first, looks like an easy lameness.

This following case presented as a right forelimb lameness by a referring veterinarian, who is also a very good friend of mine.  He is an experienced equine practitioner with years of lameness experience.  He was convinced that the horse has a right forelimb lameness, but could not block it out, so sent it to me for a 2^nd opinion and further workup.   When I looked at the horse I saw what I thought was a right forelimb and right hind limb lameness.  My first thought was the first part of the “Law of Sides”, i.e. the horse truly had a right hind limb lameness with a compensatory but false right forelimb lameness.  The Lameness Locator results showed very clearly that the vertical pelvic movement pattern was a classic compensatory pattern for primary right forelimb lameness; an ipsilateral (right) hind limb impact type lameness, and a contralateral (left) hind limb pushoff type lameness.  Without the Lameness Locator results I may have become flustered with the subsequent results of the many blocks that we later performed on the right forelimb.  Did we really have a right forelimb lameness, or should I block the right hind limb?  I stuck to my guns because of the Lameness Locator results and finally blocked the horse out to the shoulder.  The point being that, even in the apparently easy cases (I would have thought the horse had a right hind limb lameness), you just cannot tell until you are well into the case, whether the Lameness Locator results will be helpful to you.  Deciding to use Lameness Locator in the middle of an examination, as a second thought, is added work.  You have to go get the sensors, apply them to the horse, re-trot the horse up and down, and it is just a pain in the neck.  Putting the sensors on at the beginning of the examination in all lameness cases prevents this added work.  If you do not need the information and you find just what you thought you would find, then nothing is lost.

I have used this approach, putting Lameness Locator on all my lameness cases, for the last several years.  I have yet run into the client that is not willing to pay the few extra dollars (we charge an extra $75 per lameness evaluation when Lameness Locator is used).  Most appreciate the extra objectivity and are interested in looking at the results themselves.  

this is just a practice run

this is just a practice run

When lunging, use Elasticon to prevent gyro sensor rotation!

I do not know exactly why it is that the gyro sensor has the propensity to rotate around to the back of the limb when the horse is lunging, but it does.  Usually you do not actually see it rotate, and, frequently, you do not even notice it sitting on the back of the pastern either, until it is too late.  You just see weird results.  Hopefully it is noticed and corrected.  Worse yet, it could go unnoticed and decisions get based on wrong results.  Here is an example.

This horse has obvious left hind limb lameness with a suspected compensatory left forelimb lameness.  This is the baseline straight evaluation.

But, then the horse was lunged and evaluated, as usual, first to the left and then to the right.  When lunged to the left the left hind limb and left forelimb, which is most likely compensatory, are easily seen. 

The horse was then lunged to the right.  Obviously something is not right.  The report now indicates a right hind and right forelimb lameness.  While trying to reconcile this in our heads, i.e. we are seeing a left hind and the computer is picking up a right hind, someone noticed that the gyro was on the palmar aspect of the right front limb.

You cannot tell from the results when the gyro started rotating and when it actually reached the palmar aspect of the right front pastern.   It could have started rotating anytime between the start of collection of lunge left and end of collection lunge right.  Here is the problem with a rotated gyro.  It is actually a fairly complicated situation.

1.  The gyro does not have to be “exactly” on the dorsal surface of the pastern.  As long as it is approximately on the dorsal surface the collection and analysis will be OK.  We have not studied this in detail but my guess is that as long as the gyro sensor has not rotated so much that it is on the extreme medial (it usually rotates medially) or lateral aspect of the pastern the analysis will be correct.

2.  When the gyro rotates 90 degrees such that it is on either the medial or lateral aspect of the limb, you can expect anything and everything.  Sometimes the analysis will be correct, sometimes it will be exactly opposite, sometimes it will switch back and forth between limbs, and sometimes an analysis cannot actually be performed (i.e. the software will crash).  This is because the software cannot decipher the timing of right forelimb stance correctly, because the right forelimb gyro signal is weak.  It may happen to get it right, it may happen to get it wrong, it may break up the trial into segments and sometimes get it right and sometimes get it wrong, or it may not even recognize the second or gyro channel as something coming from a horse, so…. it crashes.  You can see this is what happened in the lunge right collection for the forelimb evaluation.  .

3.  When the gyro rotates 180 degrees such that it is on the palmar aspect of the limb, you can expect the results to be exactly the opposite of that reported.  Right becomes left and left becomes right.   This is what happened in the lunge right collection for the hind limb evaluation.

Here, by the way, it the correct evaluation, after we put the gyro in the right orientation and recollected the data.

So, just as a matter of course, if I am going to evaluate the horse during the lunge, I simply place a single strip or throw of Elasticon around the top edge of the pastern wrap, as shown.  This will give you peace of mind and save you from a few headaches.

Philosophy of Lameness: Using Lameness Locator to “chase” a second lameness.

Finding a horse with a hind limb and a forelimb lime that appear “lame” is a pain, for you and the horse.  I have always struggled with what to do in a situation like this. Using the inertial sensors, which is more sensitive to detecting asymmetry of torso motion, which could be due to lameness, may make this determination even more difficult.   This is especially true since hind limb asymmetry, which may be difficult to pick up with the naked eye, is easily picked up with the inertial sensors.  I am, at least partially, guided by the “Law of Sides” that proposes that the most significant problem in an apparent ipsilateral lameness is the hind limb, while in an apparent contralateral lameness the most significant problem is usually the forelimb.  This first part of the “Law of Sides” is generally true, but the second part is somewhat misleading.  In fact, horses with primary forelimb lameness will have what appears to be either, or both, an ipsilateral hind limb impact lameness or/and a contralateral hind limb pushoff lameness.  Close consideration of these observations quickly uncovers a “chink in the armor” of “The Law of Sides” for peeling out these multiple-limb lameness problems.  Where is the likely primary problem in a horse that has an ipsilateral lameness and the primary component of the hind limb lameness is “impact”.  It could go both ways.

This is where patience and experience and, if I might add, a realization that not every case follows the rules, is your strongest ally.  This is also why putting the inertial sensors into the hands and use of non-veterinarians is a recipe for disaster.  Here is a case with an apparent right forelimb and right hind limb lameness, which is primarily impact in type, which ended up being a primary right forelimb diagnosis.  It was the history given by the owner, and maybe flexion tests, which helped to sort the case out.  In addition this case shows that a significant effect of the block may be a change in the type of lameness, rather than simply a reduction in amplitude of vertical head movement asymmetry.

Here is the baseline straight.  Subjectively the horse maybe had a very mild right front.  Nothing was certain in the hind.  From this report we see the right front (4 strikes) and the right hind (3 strikes).  The right hind is of impact type.

This is the conundrum.  Should I go with the right front as the primary or the right hind as the primary?  The owner helped here, by indicating that the lameness, now about 2 weeks old, was more dramatic and, he thought, right front, several days prior to presentation.  Flexion tests helped also (not shown), with a right hind flexion test negative, and a right forelimb flexion test positive.  But, it was still an educated guess.

Here is the result of a right forelimb biaxial, palmar digital nerve block.

No change, at least not in the right forelimb.  The right forelimb is a little worse.  The right hind limb is now below threshold.  Just maybe I picked the correct limb to start blocking.  Also, the horse did not look any different subjectively.

Here is the result of a right forelimb biaxial, abaxial sesamoid nerve block.

In addition to the horse looking subjectively better, we can see a dramatic shift in the type of lameness from primarily midstance to definitively end of stance. Notice that if only the a1/a2 value was being tracked, this improvement in block would not have been “picked up”.    Uh oh, the right hind limb lameness is back, but not it is pushoff and impact.  Could this be a true lameness or some weird compensation from the block?  Don’t know yet.

Here is the result of a right forelimb biaxial, low 4-point block.  Not much different than after the abaxial sesamoid block, except that perhaps both right front and right hind are slightly better.

We ended up radiographing the right front limb and found an OCD lesion in the medial condyle of the pastern.  Because of the history and age of the horse we decided at this time not to pursue the potential right hind limb lameness.  Although we were picking it up with the inertial sensors, we were not “seeing” it and it was not part of the problem originally suspected by the owner.

The purpose of this case presentation was merely to point out a few; 1) ipsilateral lameness with hind limb impact type can be difficult to interpret, 2) do not rely only on a1/a2 values to detect improvement after blocking, 3) sometimes the most dramatic change after blocking is a change in the type of lameness.  One other point is worth mentioning, and actually this is the main point of the post.  Why did I not “chase” the potential right hind limb lameness?  Now we are getting more into the “philosophy” of lameness than into understanding the specifics of the LL report, but it has just been my experience that chasing after a second lameness (after you think you have found the primary lameness), is usually a futile exercise.  Secondary lameness can occur frequently and this lameness can be either in the same limb or other limbs.  I think this is usually from overuse or overstress secondary to the primary lameness.  Usually this secondary lameness is widespread within an affected limb and almost impossible to block out.  Anyone who has had an iliotibial band syndrome secondary to primary leg lameness in the other side can attest to what I am getting at.  If this right hind limb is persistent and is seen at recheck examination, I will think more of it.