Do I have a minor knee sprain or is it more serious?

[Shawnteee]

While playing racket ball the sole of my shoe stuck to the floor causing my ankle and knee to slide outward. I felt my knee buckle. I am not experiencing any pain unless I twist my knee. There is a small bulge on the outside of my knee cap. No popping noising when I bend my knee, it is hard to totally bend due to tightness from the swelling.  I can put weight on it, but having to be really careful walking due to any twisting motion causing pain. Mostly I'm concerned about the one area that bulges out because there's almost no other swelling.