Sorry about the accident. That's a bummer. So, your main question is about the cartilage thinning in your knee? I found this which might help. https://www.sportsinjuryclinic.net/sport-injuries/knee-pain/acute-knee-injuries/knee-articular-cartilage-injury Your accident could have caused this or it could have been happening over time. But either way, that is now seen, it's now a fact of your knee. Sorry about that! RICE is often applied to help with it. (rest, ice, compression and elevation) to reduce swelling. Doctor can give a professional ice wrap. If doc says it's okay, you can take ibuprofen. Some people are okay with just that. Others may need surgery. So, like everything, this will depend on the severity of your actual state of cartilage thinning.
When are you seeing a doctor next?