Back knee pain - hurts when cross-legged! Please help!

Hi guys, I'm a 22 year old guy. I'll also mention that I have flat feet (no arch support).

I'm been having this strange pain in the back outside part of my knee. I don't think it has anything to do with the joint itself or the kneecap. I can squat just fine with no pain and support my entire weight on that knee no problem (quads tensed).

However, the pain is initiated when I try to flex my leg against resistance (i.e. when I try to "fold" my leg). It also hurts a lot when I try to sit cross legged, or when I'm sitting and I try to put the ankle of my injured leg on the knee of my healthy one. I don't know what initiated this injury, my best guess is that as it's in my left leg, its due to clutching action of my car, which I've had about as long as the injury has been present, I think.

I read up about a few problems. My knee feels very solid and doesn't give out, so I don't think it's my ACL. I've read about the popliteus muscle, and it seems to correlate well with my symptoms, but then again it also seems to be a very rare condition. I also read about ITB, but it doesn't seem like that would be my problem, considering that I don't really run. I did play badminton once a week but never experienced any pain during gameplay (not that I noticed anyhow).

Does anybody have any insight as to what the problem I'm having can be? Thank you very much in advance!

[peetss]

i'm 23, flat feet and i'm having the same problem as you; only hurts when i put the ankle of my leg on the knee of the other...

as my ankle hangs naturally in this position the pain is there however if i lift my ankle with my hand the pain subsides... this has been an issue for me for awhile now and i have no answers... anyone?