The short answer to your question is not necessarily. There are a number of reasons your new knee might be unstable-- some of these could be related to medical negligence and others are not. The only way to know for sure is to get your medical records (and the imaging studies too) into the hands of competent med mal lawyer and let him or her evaluate your case.
I think it makes sense for you to be worried about trusting the same doc. Head to a large, university-based medical center and get evaluated there-- these are the places that spend a fair amount of their time fixing things that have gone well elsewhere. You might not like the travel, but it's likely to be worth it in terms of expertise.
I wish you the best.
Answered on Aug 27th, 2012 at 3:27 PM