knee pain in the rear of knee when bending and straighting under weight I am experiencing sharp pain in my left knee when i squat. when i extend my knee back straight I experience pain. Standing on my left knee and lift and bend my left up without any weight it experience pain in the back of my knee. I also experience pain straighting my knee back straight. I slao experience pain when lifting my knee while putting on my pants. Just standing straight up i get pain in the back on my left knee just standing straight legged. I also have alot of side to side movement with the tibia area at the knee.