While I haven't been to a doctor to be diagnosed, I'm very certain I have the same problems in both knees.  I believed I injured both knees in the 80's while riding up steep mountains in PA. on a very cold morning.  The good news is that since then I've learned coping skills such that in '04 my wife (with a new knee) and I rode around Lake Erie on a Duplex. In '05 I rode the Trans-Am West to East (Oregon to Yorktown VA to Harrisburg PA) on a Slipstream and this year I rode from Phoenix NY (near Syracuse) to Freeport Maine.  Here's what I've found.   1 st. - Most important. Keep the knees WARM at ALL times.  I wear fleece lined tights all year and on cool mornings additional windproof covering over my knees.  2.-  Wear Cho-Pat braces.  The ones with two velcro straps.  They are excellent.  3.- Take 3 ibuprofen tablets at breakfast and 3 more at lunch. (You want to take them before the pain and inflammation starts).  I didn't follow my own advice this summer when I rode thru the Adirondack mountains and my knees got cold and very, very  painful. I almost quit.  Then I woke up and realized my knees were getting cold through the tights. I took paper towels folded them to 10 thicknesses.  I put them under my tights, over my knees and held them in place with the cho-pats.  A day later - no problems.  4. - Gear down - 24 front and 34 rear to keep pressure reasonably low. 5. - If pain starts - Take a break and maybe tighten the Cho-Pats.  P.S. I'm 66 - Don't give up!  P.P.S. - I didn't find Chondroitin helpful at all but many others have.