I tore my ACL playing football back in October, and had ACL and lateral meniscus surgery with a hamstring graft in November. I am now 22 weeks out. I was working out in the gym yesterday and was doing single leg leg extensions, and decided since I was so far out I could challenge myself a little. about half way through my reps I got a moderate pain in the middle of my knee and on the inside of my knee starting about mid quad and running down to my calf. So I stopped doing the leg extensions and went on with the rest of my workout with no problem. Then when I was exercising today, i.e. running, I ran one lap fine, my knee felt great, then when i took a turn half way through the second lap my knee started popping and having a grinding sound, I got a pain on the inside of my knee, and my knee felt weaker. I also had the pain on the inside of my knee when I was doing my quad stretches at the end. After the workout, after sitting for a little while when I started to walk my knee felt really stiff. Is this something to worry about, and get checked out, or did I just over work my knee?