hi, concerning to the fall on the knee, it might be infrapatellar bursitis and also hoffers fad pad might be inflamed. if tibial tuberosity is painfull, osgood schlatter might be the reason.
if you want to check lig (ACL) use lachmann test, you only need about 30 to 40 degrees od knee flex. Pcl gravity sign might be useful.

cheers