Hi. I have been experiencing pain in my right knee (dominant). I caught the inside edge of my sneaker on a thick mat that you would typically find in a factory. I felt a sharp pull on the side (toward my other knee) of my kneecap. Since then I have had a great deal of pain. When I walk any distance the pain shoots down my shin just below my knee to the outside of my leg. It is painful when I am in bed even with a pillow between my knees, I sleep on my left side. I have found though that if i keep my leg straight at night it helps to ease the pain. After I have been sitting it is very painful to stand and begin to walk. I can feel that it is swollen even around the back of my knee and is painful to bend.
Dear sir /madam What is your age?  It could be:Internal derangement of knee, for which immobilization in knee immobilizer is recommended. Or it could be acute exacerbation of osteoarthritis in the knee.  Take Care!  Regards