I've been studying TKD for a few years now but am having to stop because of problems with one of my knees.  I've managed to tear the meniscus and damage the cartilage in my right knee and will probably have to have surgery later this year to fix it.  The doctor has said that all of the low stances in TKD probably contributed to the injury and I will not be able to do any stance that involves placing a lot of weight on my knee in an awkward position after the surgery.

Is there a decent martial art out there that:

- teaches useful self defense techniques
- provides a good work-out
- doesn't involve a lot of stances that put a lot of strain on the knees

Jujitsu perhaps?

We had a guy who had arthroscopic surgery and returned to get an aikido shodan.

Still some low stances but not as hard on your body;  footwork similar to swordwork.

With TKD you have a lot of the striking work already so some joint manipulation and throws will be a useful complement.  Check out aikido - just make sure it's closer to aiki jujitsu, the precursor art - some aiki gets very airy fairy.

I would get a second opinion.  There's been guys that have come back from complete ACL tears and surgery and were able to compete at a high level.  Former UFC champ Tito Ortiz had an ACL tear/surgery/rehab and was able to come back and fight again competitively.

I'm not saying to disregard your Dr.'s advice, but I'm not sure how familiar some of them are with martial arts.  Maybe see a sports Dr. for a second opinion.  Nothing wrong with learning other styles, but I would hate to see you give up years of TKD based on what a Dr. said, especially if it's not necessary.  

Lester, that's good advice.  I've had two different doctors and two different physical therapists tell me that I shouldn't do the low stances.  I'm still going to try to ease back into TKD (very slowly!) and see if I can manage the low stances without hurting my knees again.  I'm not expecting to be able to do it though and want to have a "Plan B".

Don't think I'd do jujitsu with knee problems.  I know two different people who tore knee ligaments in BJJ.

Might try something like Modern Arnis or some other Filipino martial art (FMA).    

I had a similar issue, bt was fortunate enough to avoid the tear and surgery...I was a TKD student also.
Try Aikido it has very useful non stressful practitioner  technigues that ar every effective

JuJitsu includes LEG SWEEPS,,, very bad for joints like knees that are suspect

Although Aikido might seem like a decent choice, I think the kneeling techniques (suware-waza) and the constant throwing and standing back up would be hard on someone with bad knees.   Also, depending on the mats (non tatami) used in a paticular dojo, doing some Aiki techniques such as Shihonage and Iriminage on softer mats puts a lot of strain on the knees.  

UPDATE- I've found a guy that teaches "self defence" classes with a very broad backgroud - TKD, Karate, Hapkido and some other stuff.  I've talked to him and it sounds like it is at least something to try.  He doesn't emphasize low stances or forms like a normal TKD school would.  Best of all, he is teaching because he likes too -- he doesn't charge for it.

I'm keeping my fingers crossed that my knee stays in once piece, because life without MA would be boring!

Be carefull you may be getting what you pay for.  

First off as a Black Belt in TKD I will say TKD is useless and sucks horribly for self defense.  Try a real stand up style like Muay Thai or American Boxing.  Any wrestling discipline is a total different workout and type of conditioning than stand up.  You can go for round after round and run miles every day and still be gassed in under 2 min on the mat wrestling (BJJ or any other)