i had some cartilage impinging my left knee joint a few years ago and it had to be removed...while they were in there, they chipped off all of the bone spurs that were growing on the surfaces that were unprotected due to a complete lack of articular cartilage (osteoarthritis)...i was told that i needed my knees replaced...after a number of mri's i was also told that my hips weren't far behind...since then i went in once a year for supartz injections in my knees...haven't been back for over a year, though...i reduced or eliminated the impact exercises from my life (no more running and shit like that)...for cardio i use the elliptical, the rowing machine, a spinner bike and the heavy bag...and i cut back on the squats (i rarely, if ever, go past 225 and i never go past 90 degrees)...my knees actually feel better now than they have for quite a few years.
rehab was pretty long and pretty painful but the supartz definitely helped as did the electrical stim therapy...i'm going on 6 years now, since they told me i needed new knees...and i'm still using my OEM's.
chin-up, lad...you'll be fine!!