Ever since I tore my ACL the cold really seems to affect my right knee. I'm trying to find a good knee warmer that isn't too tight and doesn't bind up behind the knee. Does anyone have any ideas ? It's not uncommon for the morning temp to between -2 to -10 so it needs to be fairly warm and wind resistant.
Get some wool tights, they're warmest, Swobos are great. For temps you mentioned layering would be manditory. (27 yrs year 'round experience talking, with winter tours.) The Synthetic stuff that I've tried, never seems to be as warm as wool, they're ok with wool under/over them though. I know about the knee sensitivity- I have both missing and replaced parts, in both knees, including ACL
In Wisconsin, it gets very cold in winter with wind chills sometimes -60 C. In January, it is not unusual to have -15C to -20C. Still, that can't stop you from bicycling, and some areas of your body which may have been injured in the past tend to get cold as you described.
Rather than trying to focus clothing on the cold limb, it is better to try to keep your whole body warm. The warm blood will find it's way to the cold part of your body.
Wear long underwear, a hat, and good wind resistant pants and jacket. It works for me and my friends. I hope it works for you too.