Okay So I Hit My Knee Against A Metal Railing

Okay so I hit my knee against a metal railing and right after I hit it, It started hurting and I laid on the floor in pain and now its still in pain and its swollen not like really bad but at least like a ping pong ball at least and I can't really bend it back b/c it hurts and wen I walk down stairs it hurts and upstairs and well that's about it so my question is what is wrong with my knee did I fracture it or dislocate the patella or something?