There is a very interesting paper in the November edition of the Journal of the American Academy of Orthopaedic Surgeons, looking at which patients will benefit from a Knee MRI scan ordered in the Primary Care setting.
The findings of this paper show that when a patient has a history of an acute knee injury, a short duration of symptoms or a subjective sensation of instability – these patients are more likely to have positive findings on an MRI scan. When examined clinically, the patients with an effusion, joint line tenderness +/- clinical signs of instability are also more likely to have positive MRI findings, which will influence their treatment.
Thus if patients do not have an acute injury, have chronic symptoms and do not describe instability; it is preferable to hold off on requesting an MRI until they have been seen by the Orthopaedic surgeon. In many cases, weight bearing plain radiographs of the knee are more informative.