What Causes Pain In Leg While Straightening It After A Lipoma Removal?

In 1993 I had a lipoma removed from the top of my knee cap. In 2002 I started to experience pain on the inside of my right knee. The orthopedist told me that the lipoma had grown back and that's what was causing my pain. He did another operation. Ever since then, I've had pain on the inside of my knee off and on. One orthopedist told me it was referred pain from having fib-tib arthritis. Over the last few days, the pain has been intense when I go from sitting to standing. Last night I was laying in bed with my legs curled up. When I tried to straighten my leg, the pain was so intense I cried. After about 30 minutes of trying to relax it, I was able to straighten it out. Any thoughts? Thanks! Age 52 Height 5'6" Weight 220lbs