I didn't suffer a traumatic injury like you did, I just started with osteo-arthritis. The symptom was pain through the kneecap, as though something was trying to burst out! This was accompanied by involuntary muscle weakness, my body would not "allow" me to ignore the pain, my leg or legs just went weak. The effect was that at first, I couldn't get up long hills with my usual speed. Later on I couldn't burst up short hills or out of bomb holes. No more pedalling stood up!
In an attempt to address this, I reduced the size of the front ring, then increased the range of the cassette. I ended up with a 10-50T on the rear and a 30T on the front. I also went to see the physio and did all the exercises she gave me. I wore KT tape below my knee caps, I applied pain-killing gels to the knees and I took a 400mg Brufen 30 mins before every ride. I didn't start this all at once, those measures escalated over a few years. By the middle of last year I was down to an mtb ride of 10 miles with 3 days off before the next ride. My next step was going to be an elliptical front ring. But then I took a test ride on an emtb. I had been aware of them for several years, but was resisting them as I felt that I was not ready to "wimp out". All I can say is OMG!!
What a revelation! Over the next several months I went on every test ride I could find and rode as many bikes as were on offer. In all I rode eight different emtbs plus some variants, each of which passed the look test (I am not a fashion freak, but I will not buy an ugly bike). I was astonished at the impact that only 250 Watts can deliver, I've got a more powerful light bulb outside my house!
I bought a Focus Jam2 in Jan this year and I feel transformed. I can easily do 20+ miles where I used to struggle to do 10 and I can do it again the next day. My number of hours exercising has rocketed, but the unexpected bonus is that because my knees are not being as physically stressed, it feels like they are recovering! My knees no longer hurt whilst walking and only twinge when climbing or descending stairs.
Because I couldn't keep up, I stopped riding in the hills or going on long rides with my previous riding buddies. I hated being at the back or being the one everyone is waiting for at the top of the hill! I have since ridden again with friends who ride non-assist mtbs and it is tricky. I dial back the assist, but it is not easy especially on the climbs. I think that I am going slow up the hill, but my mates see me rocket away. They are still faster than me downhill though!
However I am starting to develop new riding buddies that have emtbs. I am once again happy with my lot.
@rolcher, you may believe that emtbs are the Devil's ride, not fit for proper sportsmen, but do yourself a big favour and give one a go. If you don't believe me check out YouTube and see how many top riders are training on emtbs. See what they can do! An emtb will allow you to ride where and when you want and allow your mangled knee to recover. I wish you the best with your recovery.