I just read the MRI report on my right knee. I find it hard to believe but nothing is torn. I do have some chondromalacia (deterioration of the cartilage under my left knee cap). I ride a bike but I have runner’s knee. Frankly, given my symptoms, I find this a bit hard to believe.
I did some research and found that one way to fix chronic knee pain is to use shorter crank arms on your bike. (This is pretty common in the recumbent world.) The reason is that you have less flex in your leg at the top of the pedal stroke when you push down. (This is exactly when my knee aches.)
All of my bikes use 175mm length cranks which come stock on bikes for people my height.
So I have a question.
Do you use cranks shorter than 175mm?
A Few Spokes Shy of a Wheel 
No
Well you have gotten good news MRI wise. Ok no structural, fixable condition. So I imagine your only option is to try and give your joints a rest. Repetitive wear and tear can only be fixed by reducing the repetitive action. Not what you want to hear, but if I remember correctly you switched from running to riding because your body wouldn’t tolerate the running. Maybe alternate swimming with riding? I walk 6-8 miles a day. I have thought about running, but am very reluctant to because of fear of injury which would then force me to the sidelines. From what I read you road thousands of miles, but never gave your body a reasonable recovery. Even the Nats take the winter off.
You should go and get a professional bike fit. Tell them your issues. Bike fit can make a huge difference.
i’ve ridden 175s for years. My “beater” MTB -which never gets ridden off-road- has 180’s. My left knee has been dodgy since i was in high school and years before i got into cycling. When i was riding stock-equipped bikes with 170s my knee was still dodgy. My old track bike had 165s and they felt weird- i eventually put 175s on that bike & before folks shrink in horror at that idea, i never struck a pedal in the banking. i’m not particularly long legged, except perhaps in the femur. 5 millimeters make +/- should make little difference IMHO.
There’s an anectdote about a local racer here who would change crank arms for different race conditions. One day he found in his kit a 165 L & a 177.5 R arm. Checking his bike, he found the matches -he’d been riding that way for weeks.
Thanks. With today’s diagnosis I think I’m going to leave the cranks alone (I’d have to change them on all 4 bikes). I’m not all that optimistic about PT but the cortisone shot should help a lot.