It sounds like you have a torn miniscus and some arthiritis as well in your knee. I have had surgery on both knees for the meniscus tear and NOW have had total knee replacement as I got older (58) . I had a very active life ...playing softball for many years and jumping from big trucks, climbing ladders..etc. along with a family history of arthiritis and degenterative disc disease in the spine. This comes with age and some family history. You MAY NOT recall the injury or it may have slowly just happened. I can tell you that the surgeries did help with pain going away. I was back to work with in weeks , Good luck to you.