Aikido or Muay Thai

I have not been here in awhile. Last time I posted I was training in Shotokan Karate. Since then I had taken a break from martial arts because of lack of time. Also since then the school I was studying at has closed.

I'm looking to get back into martial arts in a few weeks now that I have more time to spare. I'm looking at Aikido and Muay Thai.

I have tendonitis in both of my wrists, and bad lower back and a weak left knee. I'm also a professional musician so I have to be careful when it comes to injuries so as to not effect my drumming career.

What I'm looking for most in a martial art is a style that teaches one how to fight well if need be in a street situation and also something that is good for exercise and that I can do long term. I also need a style that I can practice solo as much as possible so I can still train by myself when I'm on the road touring with my band's.

What do you all think is the better fit for what I'm looking for? Aikido or Muay Thai? I'm also open to other style suggestions. Thanks!