Hi, im 23 and im having a problem with my knee, all of a sudden 3 weeks ago my knee felt like it gave way, ive been unable to straighten it fully, however this week i managed to straighten it but as soon as i put my weight on it stood up it gave way again. I have been to the hospital and xray was normal, im waiting for a scan but this is 4 weeks. please help or advise?