With any reconstruction work you will get (a) scar tissue that needs to broken down to resume normal functionality (b) muscles will also overcompensate any issues and so you may have an muscle imbalance. ensure you train (i presume you do as you mention leg curls) - be sure to train laterally and medially (inside and outside mucsles) for example - leg extensions, you have 4 quad muscles, all need to be balanced and trained equally for optimum knee functionality. With regards to scar tissue - deep massage treatments will eventually break this down.. when did you have the operation?