knee fall, maniscal damage?

[Emanuele]

Anterior draw is not reliable as a test in acute events, however considering the mechanism of injury you had, it seems unluckily you injuried your cruciate, unless if in falling down you didn't awkwardly twist your knee, then that would change the scenario. Possible post traumatic sinovitis could be taken in account but the fact that your knee has swollen so rapidly doesn't convince me too much

Did you have a big cut over your knee?
Have you got fever?

however you said you can fully flex the knee so I guess the swelling is subsiding otherwise you would have struggled.
Damage to the cartilage would have possibly given you "joint mice" and you would have had some problem on flexing or extending (not always though)
Plica tends to be quite pinpointed as a problem, mostly just medially to the patella and anyway not easy to diagnose (usually by exclusion or with arthroscopy)

More than an X-ray, MRI is indicated.

Let us know how you are proceeding!

All the best!