Welcome at healthcare magic.
I feel sorry to hear about your accident.
It looks that you are worried about small lump over the knee.
Underneath skin & in front of knee we have a pocket of small fluid containing structure which is present in normal person.This structure is known as bursa.The collection of fluid in this bursa increases whenever there is infection ,inflammation or trauma.
The present swelling is in this bursa is due to trauma,you are having PRE PATELLAR TRAUMATIC BURSITIS
At present you should do cold
fomentation over it & take an anti inflammatory analgesic
.This will give you relief.
With best wishes.