First, your doctor will compare your painful knee with your healthy one.
In addition to redness, swelling, bruising, and discoloration, your doctor will check for differences in your muscles. Knee pain often happens the when the outer muscles of the thigh are stronger than those in the mid-thigh.
You doctor will also feel your knee, checking for pain, warmth, and swelling. He will then move around the knee to feel for injury and find out how well it moves and where the pain is.