As per your description few points requires clarification
1- what is more troubling is it pain or instability (feeling of insecuritywhile turning around or running )?
2- Is there any episodes of locking of knee joint?
3- Is there a swelling now?
4- what is your age ?
5- was the patella (knee cap) alright after the fall ? any slipping?
6 - Have you been seen by an Arthroscopic and sports medicine
specialist after the fall ?
IF minimal or no pain the problem is mostly ACL injury
if pain and swelling is the problem most likely is a cartilage
or meniscal injury
if swelling is the major problem rather than pain mostly is due to bursitis
if knee cap is abnormal may be due to patellar dislocation.
if at older age group with swelling it may be the acute exacerbation of the existing .
PLEASE DO CONTACT ME OR AN ORTHOPAEDICIAN WHO IS WELL TRAINED IN ARTHROSCOPY
AND SPORTS MEDICINE.