Because my pet peeve is threads with no resolution, I want to update this in case anyone else find themselves in a similar boat.
The first vet that blocked him localized the lameness to the correct foot/portion of the leg, but not quite the right area of soft tissue.
After a few months of up and down rehab, I had a lameness specialist come out. He did an ultrasound and found a large lesion in the left branch of the SDFT in the pastern and a smaller lesion in the right branch.
We did shockwave monthly for 3 months, and I did cold laser almost daily in the interim (though not on the same day as shockwave, obviously).
The horse improved dramatically over the course of a month, and by the end of 3 months, he jogged sound. I walked him under saddle through most of this because, as the vet said, you can’t really hurt him by walking him under saddle. I don’t weigh much, and he’s a big horse, so I didn’t feel I was unduly burdening him, and the resistance was good for him. During this time, we only walked on very firm surfaces–concrete or dry, flat, grass fields. Avoided the (only slightly) deeper footing in the ring until he was consistently trotting well on the grass.
Fast forward to current day, and we basically made it through rehab and a BRUTAL winter this past winter with no major setbacks.
For various reasons (weather, his other health issues unrelated to this lameness, etc), we had to wait until this spring to really get back into consistent rehab, so we started at trotting 30 seconds in each direction, and increasing the total trot time by 1 minute per week.
We always start with 10 minutes of walking to warm up.
I add 7 seconds in each direction, each ride, as long as he feels solid because I ride him about 4 times a week, about every other day, except on weekends, when he is ridden two days in a row, and then, depending on how tired he seems, I sometimes keep the time the same on Sunday as Saturday.
He has been sound for the duration of this rehab, which is just incredible. I laser him afterwards each time.
We are currently at 4 minutes and 21 seconds of trotting in each direction, and when we get to 5 minutes in each direction, we will add cantering… one lap each direction, and increasing by one lap per direction each week.
It’s been over 2 years since I cantered my horse (on purpose–there have been a few spook steps that don’t count haha).
So… long story short… time and very, very incremental rehab, and no small measure of luck, and this horse is functional again. I am still being very careful about footing, turns, time, etc.
As I keep telling him, we are doing this so he can go run around and have fun without being in pain afterwards.