Have you had many doses of IVSM? Steroids can cause bone deterioration , particularly the hips and femoral head, as well as muscle wasting. Might be something to look into ,as well. It is unusual,but common enough,I guess, since my neuro warns me everytime steroids are mentioned.

http://www.drugs.com/pro/solu-medrol.html

You have to scroll about halfway down, but there's some good info on the more interesting "side effects".

Another thought - if your legs hurt more and your balance is worse, it's possible to have a compensation injury,where you put extra stress on the "good" side while compensating for the bad one. When my balance first went screwy, my left knee started hurting like crazy...turns out the way I was walking in an attempt to not fall over was putting a strain on that knee.

I hope whatever it is, the docs can find a treatment that gives you some relief.