Julie, a 21-year-old soccer player, is running down the field when she plants her foot awkwardly and twists her knee. Her knee buckles, she feels a pop, and she is unable to walk. The knee swells within hours. Julie visits the hospital and has an x-ray, which is normal except for swelling (but it does not show a problem). When she sees her doctor a week later, her legs are well aligned but there is still too much swelling to tell if her ACL is torn. Julie asks if an MRI would help identify the injured anatomy.

George, a 52-year-old electrician, spends a considerable amount of time kneeling and squatting. Over the last 10 years, his knees have become increasingly painful. However, he cannot recall a specific injury. He feels the pain on the inside of his knee. Occasionally it is sudden and sharp. He almost always has a deep, achy discomfort that becomes worse when he uses his knees. His doctor recommends an x-ray.

Adam, a healthy 35-year-old postal carrier, slips on ice while carrying his two-year-old daughter. He feels his knee twist awkwardly. The next morning, his knee is swollen. Five months after that, Adam reports that he cannot jog or squat, and doesn’t trust his knee. His quality of life and work are affected. Adam has trouble with stairs due to sharp pain. He has seen a physiotherapist, and has been doing home exercises faithfully to strengthen his quadriceps (front of thigh) and gluteus (rear end/buttock) muscles. Occasionally, his knee swells.

When can MRI help with treating a sore knee?

An MRI may be helpful when:

a sore knee is not responding to appropriate treatment
the diagnosis is unclear after history, physical exam and other investigations, like X-ray, have been done
knowing more about the injury is likely to change how you care for the knee
if your knee looks out of alignment (more than just swollen) compared to the uninjured side after an acute injury.

What can MRI see?

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.

What are the limitations of MRI?

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.

When is an MRI appropriate?

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:

may be due to an underlying medical problem that cannot be identified by blood work or another imaging option
is not responding to usual and adequate rehabilitation
would be treated differently with the addition of new information, as when deciding on whether surgery might help.

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.

Private MRI testing

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.

Does my Sore Knee Require an MRI? It Depends...

A few scenarios

When can MRI help with treating a sore knee?

What can MRI see?

What are the limitations of MRI?

When is an MRI appropriate?

Private MRI testing

Does my Sore Knee Require an MRI?
It Depends...