I am 57 yrs old,had a total knee replacement in 2008.I have been working on my riding mower the last week laying on the ground and getting back up alot.Yesterday my knee started hurting right below the kneecap,hope i just strained it and not bone cement coming loose on lower part,Had a checkup and xrays 6 months ago and ortho doc said everything looked good.Don't want to panic and call him yet.It hurts walking and really hurt putting on brakes in my car.