You think a lunge is going to be easier on your RF than a squat? No, no, no. What happened to your thigh 2 years ago is already healed, and you're having problems with the scar. This can be treated with myofascial release-type massage. But if you propose to stop squatting until the pain is gone, it will be a while before you squat again. Get the massage, squat through the pain during rehab, and quit being a puss.