What causes Locking Stifle? What can you do for it to stop it? I might have a coming 3y/o mare with locking stifle I've only owned her for about almost 2 years now and her one hind leg locks up some times like every month this started this winter. Not sure whats causing this. I will be getting my vet out to check her out to see what else i can do for her to. Thanks for the advice.