What Causes Knee Pain With Swelling, Vein Pain, Bruising And Darkening?

Out of no where I had a sudden pain in my left knee. I noticed some isolated swelling. A few hours later the vein over my knee cap looked as if it had ruptured. It has continued to worsen and is looking very bruised and dark. The vein is painful to the touch. Should I be concerned and seek medical help?