Make sure you get the MRI as soon as possible. I snapped my anterior cruciate ligament, and was wrongly diagnosed with stretched medial ligaments. Nine months later I chipped the cartilage throwing a frisbee (I know, I know, and how the nurses laughed too) and during the ensuing arthroscopy my ACL was nowhere to be seen. Oh - and do as your physioterrorist tells you. When my ACL snapped I was playing cricket and all I could do to try and stop the pain was bite on a cricket ball. Entonox sounds like more fun.