Can A Knee Injury, Torn Meniscus, Leg Lump And Atrophy Be Treated?

I have had a knee injury and had surgury for a torn menicus. Since then I have not been able to lock my leg all the way back. It feels like there is a muscle or something in the way cause I can feel a small lump in the back of my leg at the joint. I now have atrophy in the one leg along with several other issues I associate to this one issue. Can you direct me in one direction or another? Can you tell me what is wrong and how to have it fixed or how to fix it myself or who to go to, to have it looked at? How would a doctor diagnos this issue because I have talked to one about it before.