Just happened a few days ago after I nice ride in some cold weather .. I thought I was done for awhile .. although I had alot of pain .. I decided to try and ride it out with a nice slow paced ride.. I rode slow for awhile but my knee felt fine .. I had a couple of days rest and then I increased my cadence using the easier gears and had a hell of a ride.. must have averaged over 20 mph for 20 miles and did not get winded .. Im guessing since I wasnt going all out I was relaxed and not pressured to reach the next level and low and behold I was there .. zooming away relaxed.. at a better level then I ever had the pleasure to ride.. my knee is somewhat sore but much better.. Im also doing sqauts when the temp gets a little low rather then ride and also some upper body stuff.. this is a great sport folks .... I love it so much .. im selling my house to move to a nicer climate soon ..
1) You really need a sports physiotherapist, if you can afford one. Doctors don't usually have the specialised knowledge of how to rehabilitate an injury, which is a complex process with several phases.
2) I'm currently rehabilitating a chronic groin muscle strain using an excellent self-help book called "Treat Your Own Strains, Sprains and Bruises". The book is available from Spinal Publications Ltd, P.O.Box 93 Waikanae, New Zealand or in the U.S. from OPTP, PO Box 47009, Minneapolis, MN55447, USA , or so it says on the back cover. The edition I have was published 1994.
3) It's really important to either get very detailed professional advice, or a very good book to guide you. If you don't & try to "wing it", then you're likely to either re-injure yourself, or fail to properly stretch the damaged area, leaving you with a shortened range of movement and thus prone to injury again.