When you state stifle problems, we assume that lameness is involved. Horses with stifle problems are going to be lame in the hind end. The lameness can be on one or both sides, depending on if one or both stifles are affected. Usually the stifle joint will be swollen and possibly painful but not always. If the problems have been going on for a period of time in one leg, the other leg may develop problems from supporting too much weight. Diagnosing the problem requires a good physical exam, radiographs, possibly ultrasound and arthroscopic surgery. Prognosis is based on the diagnosis but is often guarded. If your horse is not lame but just locks his stifle, he is getting his patella (knee cap) caught. These horses will get their leg stuck out behind them and will be unable to flex (bend) the leg. Having the horse back up slowly or manipulating the patella will normally allow the patella to release. Treatment is directed to building the muscles of the area by allowing the horse to move at will and not stabling the horse. If you have some hills in the pasture, this will also aid in muscle development.