An MRI may be helpful when:
X-ray is used to look at bones and the amount of space between them. MRI is better at imaging the soft tissues around the bones - the muscles, ligaments, tendons, and connective tissues. Joint pain and joint injuries often involve soft tissues. In this case, an x-ray will look normal even though the knee hurts.
Unnecessary use: In most cases of knee pain, a history and physical exam are enough to provide an accurate diagnosis. Often, an x-ray is the only imaging that is needed. Some patients expect an MRI, and doctors may feel pressured to order one to support their diagnosis (rather than relying on their experience). However, in many cases an MRI does not change how the knee problem is managed. When considering the value of an MRI, ask whether the test results will change the current treatment approach. If the answer is no, then MRI is likely not required.
Too much detail: MRI provides such great detail that it can create uncertainty about which abnormality is causing the pain. Even a young person can have something unusual in a knee, shoulder or lower back. This abnormality may or may not cause pain. Older people may have many abnormalities in or around a joint, making the diagnosis even more confusing. In addition, it is possible that an MRI can miss the cause of the pain. For instance, MRIs can miss 10 per cent of ACL (anterior cruciate ligament) tears in the knee, and miss labral (connective tissue) tears in the shoulder and hip more often.
Access and cost: MRI scanners are expensive and tend to be located in major centres. Waiting for MRI to confirm diagnosis can delay the treatment that might already have improved the situation.
Expectations: Finally, many patients and doctors feel that an MRI is required before a person sees a surgeon or has surgery. However, in most cases this is not necessary.
For Julie and George, a diagnosis can be made based on history and a physical exam, along with basic x-rays. Julie most likely has an ACL tear, and needs a repeat physical exam to confirm the diagnosis once her swelling settles. If there is doubt about whether her ACL is torn, an MRI may be reasonable. George most likely has arthritis in his knees and does not need an MRI. If either case does not improve with adequate rehabilitation, then a consultation with a sports medicine physician or surgeon is reasonable.
If an injury or pain is new, imaging is not usually required since many joint and soft tissue problems will resolve on their own. If diagnosis cannot be made with a basic history and physical exam, an imaging study may help. Depending on the likely diagnosis, the doctor might recommend an x-ray, bone scan, ultrasound, or CT scan before requesting an MRI.
MRI may be appropriate if an injury or problem:
Adam’s problem is not resolving with reasonable and consistent rehabilitation. He most likely has a meniscal tear. Using MRI in his situation might be warranted. However, even in this case, it is not likely to change how Adam’s sore knee is managed. Waiting for an MRI should not delay referral to a surgeon.
In many centres in western Canada, MRIs are available privately for a considerable price. Be very careful before spending money on a private MRI, as you may not gain more information than you already have. Ask your doctor whether MRI is likely to help before pursing this option.
In general, MRIs are done for knee pain more often than they are needed. In carefully selected situations of knee pain, MRI can be very helpful. However, MRI is not necessary for the majority of people with knee pain.