It has been 2 and a half years since my TKR and I still have the tight band feeling 24-7. But Just yesterday I was in the bathroom took a step and my knee collapsed on me for no apparent reason. After a few minutes I was able to put some weight on it and walk very gingerly. Nothing seemed out of place and today it is less sore and I am walking on it. The last time this happened to me was last March meanwhile I have worked very hard to strengthen my quad and stretch my knee with a range of 105. DOES ANYONE HAVE ANY REASON WHY MY KNEE WOULD COLLAPSE FOR NO APPARENT REASON? No one in the medical field has given me any insight.