I have bone-on-bone arthritis in both knees and periodically get cortisone shots. About three weeks ago, I tripped over a kitchen rug and went down into a deep lunge; the right knee worse than the left, before I caught myself. I now have swelling and pain in the right knee and have been using a cane, but the past few days I notice a little pain behind the knee, at the back of my leg. The pain shoots down my leg a little, and sometimes pain just happens as I m sitting still. About 5 years ago I had surgery on this knee for torn cartilage; I m wondering if I could ve torn it again. Thanks for your help.