What Causes Muscle Weakness After Complete ACL Reconstruction Surgery?

Hey, I had complete ACL reconstruction surgery about two years ago and my leg still hasn t fully returned to normal. The muscles haven t bulked up to the size of my healthy leg, especially the VMO. It also doesn t feel as stable or as strong at my healthy leg. I completed the physical therapy and exercised it a good bit when i was still in school sports that required a lot of weight lifting and it still didn t get much bigger or stronger. What can/should I do at this point to get it back to normal?