I think it is possible that the nerve is irritated.

When I dislocated my right knee, I had a severe pain in my thigh above it, that the ortho said was nerve irritation. I had an MRI to see if there was a cyst or tumor there which he suspected, but there was not. His manual exam showed very responsive nerve trigger points, however.

The treatment finally was to inject marcaine and celestone (a steroid) in the upper thigh on the latter side of the knee into the joint. This numbed the whole area internally and the pain went away. I was then able to exercise my quads, and balance the muscles on the front of my thigh, and the severe pain I was having stopped. Also I had some displacement of the kneecap which resolved when the swelling went down, and the pain reduced.

I also had some success with Lidoderm patches. I place 1/2 patch behind the knee on the back of the thigh just above the bend, when I have pain there now, which is transient.

Pain in the thigh can also refer from above.
Compression of the lateral femoral nerve can cause thigh pain.

This thread and some others on our MP forum may be helpful for you to read:
http://neurotalk.psychcentral.com/thread140114.html

A blood clot would be my first worry after surgery. The body tends to increase clotting factors during recovery as part of the trauma stress response.

You may try using a strong antioxidant.. like grapeseed extract, to calm any inflammation that may be hanging around. 200mg a day may be helpful to quench the inflammatory cytokines that result from trauma. Some fish oil or krill oil too may help that for you.