Following a skiing accident 2 months ago where I twisted my knee, I have seen a physiotherapist and a Doctor who both suspected a Meniscus tear. I had an MRI which came back showing no tears. I absolutely cannot straighten my knee, it seems locked. If i try to straighten it I get very sharp and unbearable pain in the centre of my knee. What else could cause this if the MRI is showing no ligament or cartilage damage ?