Knee pain is the most common form of joint pain, found in a vast majority of people globally. Knee pain can arise from soft tissue injuries eg ligament sprains and muscle strains, bone conditions eg knee arthritis, Osgood Schlatters, and biomechanical dysfunction eg Patellofemoral syndrome. It may even be referred from your sciatica!
For an injured / swollen knee, RICE treatmentis usually helpful as the first line of treatment at home.