My TKR is almost 10 years old and I have lost my bend.

3 1/2 years ago I had under go 3 surgeries colon cancer, uterine cancer and a hernia. I was walking great no cane ,no walker. After about 2 weeks after that I had a hitch or you might say my knee just stopped. It has been 3 1/2 years and I have lost the bend in my knee . I have to use a walker or a cane. When this happens if I can't catch my self I fall. This is no good because I can't get up. I have been complaining since this has happened. I have had test and X-rays with no answers. I am getting an MRI on my knee and upper leg soon. Just wondering if anyone else has had this happen to them. My knee is 91/2 years old.