Who has experience with a horse tripping on one hind limb only, which occurs only while coming to a stop. This has been an ongoing issue for a couple of years now. I’ve been to two different vets and neither has been able to diagnose the exact issue. Injections, while they help him move better, do not stop the issue. I do know it is a stifle issue of some sort! Help! 

What your describing is a catching stifle. You’ll see it happen most anytime but particularly on a downward transition or even going downhill.  It’s very common in young geldings (but can happen at any age), especially this time of year. There are many causes of it including long toes behind, post legged conformation, EPM, lack of fitness, etc.

To treat it most vets will inject almond oil and iodine (internal blister) into a few different spots in the patellar ligament to tighten it up. Sometimes it needs to be done more than once. Some vets will do a procedure called stifle splitting of the ligament. A lot of times the stifle joint needs to be injected concurrently with the internal blister.

What Liana mentioned above, catching stifle....my mare did this a LOT until we treated for EPM. After she was treated for EPM, we did inject the stifle. 

I was wondering if it might be catching stifle. I’ll research that some more! 

I wonder what the link between EPM and stifle is? That is interesting. 

It has to do with what part of the spine the Protozoa is affecting. Usually it shows up in the right stifle first.

I have a gelding with very narrow joint space in the stifle that does this, if the vet doesn't have an ultrasound it might not be detectable. My vet also thinks the narrow joint space may be due to an old hock fracture but is not completely diagnosed due to a very fine thin line on radiograph in the hock.  My horse flexes lame though.  I inject every season as well as pentosan monthly.  We have discussed biostride. 

Huh. Didn't know it usually affected the right stifle first. Learn something new every day!