Hello, I am really sorry to hear that you hurt left knee.. Welcome to HCM and thank you so much for posting your query.. I read your question completely and have understood it well.. Generally if the injury is mild, it should subside in 2 weeks of Time. I am not trying to scare you but please do not neglect. I being a surgeon, we come across so many such cases. Pain and swelling indicates inflammation. But that also, means there is some kind of problem inside. What? Only investigations will tell us.. You say that you heard a loud sound. According to my experience following are the possibilities. 1. Most commonly there may be ligament injury, tear or just a normal inflammatory process. Knee joint is notorious for this. 2. Some bone related issues, especially the patella being the delicate darling of a bone. Swelling, go in favor of bone issues.. Hence, I suggest you these things.. 1. Get an x ray of the knee joint in AP and lateral views, it is basic and tell us few things like oedema and bone status. 2. If pain persists, then you may need a arthroscopy or MRI. But having said all these, I hope that your injury is not severe.. Hope this helps you. In case you need any further information, contact me. Take care friend and God bless you..