Hey Allen....I've had two knee injuries (one on each knee) and MRIs on both. I had decent health insurance that paid 95% of the MRIs, and with no ionizing radiation it's a safe procedure (minus any dyes).
The first knee injury (L) was a fall during a race, quickly got back up to race pace and felt a tear somewhere in the anterior part of knee - race over. Didn't shows any signs of healing with RICE protocol over the next several weeks. Saw an orthopedic surgeon - clinical diagnosis was a torn medial meniscus. Surgery recommended and I declined. Started rehab protocol for meniscus tears but no improvement. Got my MRI and what do you know...no evidence of a meniscus tear but a strain of the patellar tendon was discovered (so much for clinical exams. Lol). Started patellar tendon rehab protocol and saw significant improvement over several weeks. Not 100% nor anywhere near pre-injury level. Some restrictions and discomfort with too much running.
Second knee problem (R) was pain & discomfort during physical activity and instability with the knee "giving out" on occasion. I self-diagnosed as some type of ligament damage or other structural damage. Saw a sports med doc who said no ligament damage and diagnosed it as patellofemoral pain syndrome (PFS). Again, rehab wasn't working so I got MRI #2. The finding was a degenerative ACL tear, as I suspected. Rehab for chronic ACL tears worked pretty well in controlling the discomfort when running but the knee is, as always will be, unstable. All the evidence suggests it will eventually go OA if it hasn't already started.
Mainly the rehab now is lots of leg extensions for the quads, leg curls for hamstrings, calf strengthening excercises, hip abductors, core excercises - all for getting the load off the knee joint and reducing the impact forces to the joints.
And so much for clinical exams (at least in my case. Lol). The power of the MRI and a good MSK Radiologist to interpret the images. I wanted to know what I'm up against because there are different types of rehab for different knee injuries. And the right rehab can make all the difference.