How can you tell if you have torn cartilage or a muscle in your knee?

MRI. If you mean by exam. Torn muscles will have a gap in them and can be felt, torn cartilage you could feel but you cannot see. The best method to do MRI on the knee to find out.
Swelling . Persistent swelling, pain, and decreased range of motion following the initial trauma may indicate a tear. If symptoms are longer than 2 weeks, it needs further evaluation including imaging studies.

Related Questions

I am wondering if you can overstretch muscles or tendons inside your knee from doing a quad stretch? I just had surgery to remove torn cartilage

Possible. Yes, generally it is possible to overstretch. The likelihood you ripped the repair is probably low, and it would also depend on which piece of cartilage. Did you have cartilage removed or repaired? If the cartilage was removed, there's nothing to worry about but if was torn and your surgeon repaired it, I would make a quick phone call to their office to let them know what happened. Hope this helps. Read more...