Not necessarily. In the case of ligament tears of the knee, the doctor's exam has been proven very accurate. In fact, a recent study done at the University of Kentucky showed a clinical exam was equal to MRI for ACL and cartilage tears of the knee.
From a cost point of view, 80 percent of the knees scanned by MRI end up needing arthroscopy anyway. This means the added cost of the MRI could have been avoided by doing a clinical exam and jumping right to the arthroscopy. Arthroscopic exam finds the problem and allows the doctor to repair it all at the same time.