We have yet another gelding with a locking stifle...which is disappointing, but since they are geldings, we won't be breeding it on. While many people say "work it out" and "square off toes" , in my personal experience those things are only temporary fixes. Yes, they do work...in the short-term, but the stifle will always show itself again...at some point. Surgery is the only permanent fix.
The problem I found in the past is many vets either don't want to do the surgery or don't have the correct "training" to do the surgery (which seems strange to me since I've watched this surgery being done and it is a very simple procedure). I haven't started looking for a vet here to do our "newest candidate", so hopefully I will find one locally.
Like others have said, once it is done, you would never know they ever had the problem...Just make sure you have BOTH sides done...not just the leg that shows locking (usually there is one leg that locks the most or all the time), because the problem is actually on both stifles, but the horse uses his strongest leg to "prevent" locking on one leg (if that makes sense), so if you only do the surgery on one leg, the other leg will lock up. We didn't know this and that is what happened when we opted to only have the one side done...then you are looking at another surgery charge to have the other stifle done!