Muscle memory is a factor when treating long term injuries . The longer the problem has been present the longer it will take to correct. The reason for that is we protect ourselves from further pain by compensating and limiting range of motion. We start to believe we are incapable the motion we are attempting. Even when the muscles are relaxed and strong enough to have complete range of motion your brain might say otherwise for fear of pain. We have to reeducate your brain to say "I DO MOVE THAT WAY". So muscle reeducation is the biggest hurdle when treating long term injuries. It requires effort on your part to stretch, and to make deliberate movements, such as fully bending the knee when taking a step up the staircase in order to break the old muscle memory.