If a horse flexes positive on a hind leg, but has an MRI with no material findings, what could be wrong? Horse is a young-ish jumper with no discernible issues under saddle, but failed a flexion on a vetting. Thanks!
I believe that it means the horse does not have a soft tissue injury - no tears, and it does not have any breaks that were not visible on X-ray. It really depends on what part of the leg was viewed on MRI, but in my experience MRI is looking for tears.
To what degree did the horse “fail” the flexion - what was the degree of lameness? A horse that is fine under saddle with a clean MRI could potentially have flexed off because, well, most of us would. 
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What was imaged? Flexes positive to what? Is it lame without being flexed, or is it just mildly positive to flexions? I assume further imaging was done than just an MRI–or did it go straight from “positive on flexion” to “MRI of entire limb”? I would think that blocks, radiographs, even an ultrasound would be a more reasonable first step. It would be really hard to even start to guess what could be wrong without more info.
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A bit more information would help.
From a questionable flexion test here our vets generally wait a bit to repeat exam first.
Unless is a PPE, where you need answers right then.
If so, I doubt that would end on an MRI?
On re-testing, then they may not have a question, or possible more to go by, have an idea where to look, or start low with blocks if no specific idea for ultrasound.
There are not many MRIs here, that would be last resort.
Since you are there now, could use more details to form a clear clinical picture for any sensible guesses, I think.
Another possibility would be that the problem is somewhere else, the flexion test found a compensatory sore spot?
Those situations are so frustrating, hope your vets can help your horse.
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Just because one person reads an MRI (or any imaging) and says there’s nothing there doesn’t mean there’s nothing there. I’ve faced this in my own healthcare, seeing multiple specialists, being told everything was “normal,” only to finally get to someone with the right experience & knowledge to recognize what was absolutely not normal.
Has the imaging been read by a boarded radiologist? Is there an expert in interpreting MRI of this joint that can be utilized?
I imagine this horse is worth some dollars if you’re going to MRI in the PPE…I’d get some extra eyeballs on the imaging before accepting it’s actually normal.
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Did the horse flex to a hock, stifle, or ankle? How did the horse block? Based just on the info you’ve given, it may mean the wrong area was imaged.
Definitely need more info.
Thanks all! Further details, but I’m trying to avoid sharing too much. Horse crashed through a fence 6 months ago. Was a 2/5 on the right hind afterwards. Full work-up (x-rays, ultrasounds) found nothing. Blocks did not improve the horse. Flexed positive on the highest flexion (stifle/SI). After a few weeks of rest horse came sound and went back to work. It’s unclear whether flexions were ever repeated. Horse was recently vetted to be sold, and flexed positive on that leg. Otherwise sound and working hard. Potential buyer agreed to pay half the cost of an MRI, so that was done. Vets didn’t find anything of interest, and now potential buyer is trying to decide whether to move forward with the purchase, pursue some other diagnostic, or walk away.
So stifle was imaged by MRI and everything OK? But horse flexes off on stifle flexion?
Stifle was only thing imaged?
It’s hard to do a flexion that 100% isolates the stifle, or at least that’s my understanding. So there could be something else going on.
I’d look at things like how long the horse has been in work, what the level of work is compared to that proposed by the buyer, how the horse is priced, how much of a unicorn it is….
Personally I wouldn’t buy a stifle issue.
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Thank you for the additional info! I’m perplexed that blocks didn’t help the horse when it was hurt. This makes me wonder if it’s injury was more muscular than joint, and something that’s prone to being tweaked on flexion but not with good, balanced riding and fitness.
Before proceeding, if I were the potential buyer, I would first want my own vets to have access to all of the relevant vet records and the MRI read to evaluate those with the buyers’ intended use in mind.
If I were to buy the horse, I’d do regular body work and magna wave along with hill work and lots of turnout to keep it fit and fluid.
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If blocking did not resolve the lameness, I’d be suspicious it’s higher than the blocks. It’s tough to flex only the stifle, you know? Is it in the hip? SI? You can’t really flex the stifle without involving either.
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It is physically impossible to MRI the stifle of the majority of horses and 100% impossible to MRI the SI of any horses, so I’m still not sure what was imagined? Are you sure it was an MRI, not a bone scan or CT?
If the horse flexed positive higher up the limb and only the lower limb was imaged, that’s probably why nothing was found.
Was the stifle blocked when the horse was originally injured? If the horse did not block to the stifle or below originally, I would guess that the horse had a strain of some of the soft tissue higher up the leg/pelvis.
If the horse was currently working at a level comparable to, or higher than, the level I wanted him for, I wouldn’t care about a slight positive flexion at all.
Is actually amazing that the seller agreed to an MRI, especially as you have to drop a horse if you have any hope of getting good images above the ankle. A lot of people would say no way and sell the horse to the next person.
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We’re the flexions repeated with the same result? Depending on who is doing the flexions and how they are done, I’ve seen perfectly sound horses “fail” a flexion.
If the horse is sound and working happily, and blocking, imaging, and other investigations have found nothing of concern, and I really liked the horse I would buy it. But that’s up to the individual buyer of course.
I am a bit confused along with the others about exactly how the SI / stifle were imaged though.
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Sounds like that horse is sound unless someone yanks their leg up at that angle. I would advise not yanking the leg up at that angle. Buyer may or may not be comfortable with not knowing why the horse doesn’t tolerate having its leg moved in that manner, but if the horse is currently performing at the desired level, I suspect you will find another buyer who is OK with a horse with one weird flexion but clear imaging.
I haven’t sold horses in a long time but if someone had asked me to split an MRI on a sound horse that had a weird flexion but clean x-rays I would have told them I didn’t think that horse sounded like a great fit and wished them luck finding what they are looking for.
