Swollen kneecap after a fall 4 weeks ago.no pain,works fine just swollen. should i be concerned??

Yes and No: The knee has fluid or what is called an effusion under the knee cap. Over time ( 3 months) it will go away. It is not harmful just cosmetically larger knee. If you need it removed see an Orthopedic doctor for arthrocentesis. They can insert a needle and drain the fluid. It may return if the area is still healing. Fluid is natures way of making you go easy on your knee.