Agreed, stifles are tough. Tough to diagnose and treat. In the past few weeks my 11 yr old feels like the right hing slips or gives out, mostly in indoor arena only. Am using PentAussie and Cosequin asu. We are 3 shots into loading dose of PentAussie so will know more soon. If no change, next step is lameness eval. Legend has always worked great for him so i would try that too before moving to joint injections. With stifles, it can be the joint or the ligaments, and arthritis or N upward patellar fixation or stuck/locking stifle. All with different treatments too, not at all confusing!