Have you had experiences with this type of injury? What had to be done to keep the horse sound? What could they handle in the future workwise? I don't intend to sell this horse, even if we can't continue our dressage career. I'd just like to know what to expect. Thanks for reading the long backstory below, and for any advice you may have!

So, I have a 9 yo TB gelding, he never raced but has always been a bit stiff in the left stifle. Usually it's manageable, and in fact last year it was almost unnoticeable 99% of the time. When it was noticeable, he usually seemed to work out of the stiffness with lots of easy work, stretching, etc.
Fast forward to this fall. I leave for a 3 month trip to Australia, asking friends and my trainer to ride him a few times a week while I'm away. He gets about a week off before they get their act together and decide to get on him. All is going well for about a week, then my trainer attempts to ride about 3 weeks after I leave and he is majorly off at the trot, in the left hind. The decision is made to give him some time off, but his condition seems to worsen. They put him on stall rest for a few days, no improvement. Call the vet out, flex him and nerve block him, nothing shows up but he is still off. Put him on Bute for 3 days and he is still off. Pain is ruled out, which is good, but the lameness is still mysteriously there. Consultation between the vet and my trainer occurs (I am still Down Under, no one has informed me yet what is going on - but that's another story) and the tentative diagnosis is made of partial upward flexion of the patella. What this means is that his stifle locks on the left side, occasionally.
So they continue to give him time off and put him in private turnout. I hear of the vet visit, lameness in late November and am due to come home the week before Christmas. I agree that until I can see him go in person, I'd rather not have any further vet visits for the sake of my pocketbook, and since he is not in pain.
When I get home, I go out to lunge him and he seems just a little off. Nothing shows up that is particularly worrying, he simply looks a little short on that left hind. I put him in a program of light long-lining 4 times a week and notice a few hitchy steps every now and then, but nothing too serious. Once he seems 90% sound with me on the ground, which happens after about 3 weeks of consistent light work, I get on and begin the same type of program from the saddle.
As of today, I've been riding him for about 2 weeks consistently, for about 20-30 minutes each time, just walking and trotting. I've cantered a few steps once on a particularly good day, and he seemed fine. What worries me is those "hitchy" steps that happen every so often. Usually it's not a big deal at all but once or twice he's had quite a big hiccup with that hind leg. When this happens, I just go back to walking on a loose rein and feel for any further trouble back there. He always seems to recover right away from these incidents, within 1-3 steps, and we continue on our way.
I've done some research on this type of injury and it seems to me that consistent work is sometimes the key to keeping horses with this condition sound, as it strengthens the muscles around the joint and keeps the whole area tighter.
At this point, I'm going to continue with the consistent light work for another month to six weeks and then re-evaluate. The vet suggested that if he does not remain sound, an irritant can be injected in the stifle area (not the joint itself) which creates scar tissue to keep the patella in place, but I don't necessarily want to go this route if I don't need to.

Again, any advice or experiences that you can share would be greatly appreciated!

Oh - he is also on a supplement, Recovery EQ, if that has any bearing on your response.

You are right, keeping him in work will keep his stifle from locking more frequently. Hill work helps a lot. This is probably why it surfaced while you were away.

We have done two different treatments for this. The first was estrogen therapy, with the thought that hormone would 'loosen' the muscle that causes the stifle to catch. The second was making a small incision and then the muscle was cut vertically in an attempt to loosen it as well (not a highly technical description!! I know..it was a while ago). We had a lot of success with the second procedure. The pony I had was much more chronic than what you are describing. I have known people who have had success with the estrogen as well.

I found that if they really get stuck (my pony would literally drag the hind legs along) is to back up and this will usually help.

Good luck. Sounds like your vet may not have much experience with this. In my experience injecting the stifle had no effect. JMHO

Hmm, I am rereading your message... is he dragging the leg straight behind him with the toe on ground? or lifting it up really high?

Thanks for your reply FluZ. Good to hear about techniques that have worked. I think the key descriptor here is "partial", so it only shows up every now and then which is why I'm hesitant to go right to semi-invasive medical treatment. When it does show up, he drags his foot for a second and then has to...almost catch the leg up with the rest of his legs..if that makes sense. You can see the stifle catch sometimes when you watch him canter at liberty, and he definitely doesn't lift his leg up high. I realize that my description is not great or very technical. I'm hoping to take a video of him undersaddle this weekend and I'll post it when I do.

I don't have much insight other than what Fluz already said; hillwork, careful conditioning/consistency, and backing up will help if it is bad. A friend's horse and a school horse in college both had very severe instances of stifles locking; to the point where the horse was three-legged and couldn't relax the leg.

If it's a mild case you might find some good stretches/massage therapy for helping the muscles stay loose. Definitely keeping him moving and strong in the hindquarters is key.

Thanks, Rumble. Good to hear that I'm on the right track. Unfortunately, it's Ice City around here at the moment, and I live in a very flat area so outdoor and hill work is out of the question for the foreseeable future. The work I'm doing with him in the arena definitely seems to be helping, though. Thanks again for your input, I'm looking forward to hearing about others who have dealt with this situation.
What could the horses do that you guys knew? Were they still able to do the same type of work most of the time, or were they pretty much retired? Somewhere in between?

I had a horse here who locked one up and after trying injections etc. the vet had to make the incision to release it. This was three years ago, she was sold since then and is still doing very well at her new home. No issues.

I think I would find out about the estrogen injections - my friend had very good success with them. The pony is in full work with no issues.

I don't have any personal experience with this, but an equine chiropractor I know quite well has had some success treating this problem. Just another option.

Hmm, interesting. FluZ - I'm going to do some research into the estrogen thing.
Alison - thanks, I know there's a really well-known chiro around here who has worked on stifles. I'm a bit cynical about it, though, as I can't really fathom actually moving the patella manually. I'm going to look into it, though!

I agree with you on the chiro, I have used a vet who did acupuncture and blisters with some success.

Call me clueless - what do you mean by "blisters"?

Blistering is an injection of a 2% iodine solution into the stifle. The idea is that the resulting inflamation will cause scar tissue to develop. The scar tissue causes the patellar ligament to shorten and keep from "catching" - no more locking stifle.

Ooh, this must be what the vet told my trainer about. She never used that term, so I was confused. Thanks!

Starr - My understanding is that the chiropractor partly makes sure that there are no other issues making everything worse (back, ect.), and that they can also influence the muscles surrounding the patella to keep things working well. The chiropractor I'm thinking of worked in conjunction with a massage therapist.

(note - I also just realized that Rumble already suggested this. I feel smart!)

Plus, I believe that when Fluz talked about injecting the joint in her first post she was referring to blistering.

My old gelding had the same issue as well. We did some injections on him, but they didn't help much. But we did find that he would not stay sound unless he was worked daily. Any days off were really bad for him. Some of the days I would just take him on an hour long walking trail ride with like 5 mins of trotting in the end, and that was sufficient. Plus it still refreshed him like a normal day off did, if not more. In the end it became more pronounced and he really wasn't sound enough to do any significant work. He was retired for about 6 months before he colicked and died in surgery :(. But that's another story.

Thanks for sharing your experience. Did you try any other treatments?

How is your horse doing? Did you try any treatments?

I've been working him consistently, trying to get his fitness up to par so I can properly judge how much this is affecting his soundness. Some days are better than others, but he does seem to be steadily improving. Still, I am getting the vet out sometime in the next couple of weeks to talk to him in person, get him to take another look at Spyro and give me some options now that he's in shape again. I've done some research and am leaning towards acupuncture, but it will depend on if I can find a good practitioner in this area. If not, I'll probably go with the injections first.

You know that Dr. Rach does acupuncture, right?

I did not, but thanks for the tip!

Have you tried the acupuncture yet?

Vet is coming out on Monday. That was the soonest appointment I could get that worked for my schedule. Horse is doing well, actually, and we've had some really productive rides. Hopefully it will improve even more after treatment.

Good to hear, I am hoping the acupuncture will help continue the work you are doing.

Vet came out - no treatment required at this time. He is not symptomatic enough to warrant any treatment, so we get the all-clear to move on to lessons and regular work. YAHOO!!!

That is great news, enjoy the lessons!