I agree with lesternator. A bad knee is not the worst injury...

Some of my patients have had serious neck injuries from hitting the headboard, etc. One fell off the bed and cut their head on the bedside table and had to go to hospital.

It does sound like a cartilage injury. If you are walking and your knee gives way suddenly, especially when going around corners, you can be nearly certain it is.

Get it checked out with a good physio or doctor.