What Is a Knee MRI?
An MRI test uses magnets and radio waves to capture images inside
your body without making a surgical incision. It can be performed on any part
of your body, but a knee MRI looks specifically at your knee and its
An MRI lets your doctor see the soft tissues in your body along
with the bones. This allows them to inspect the elements of the knee that might
have been injured during physical activity or from wear and tear. The test can
also provide detailed images of various sections of the knee, such as bones,
cartilage, tendons, muscles, blood vessels, and ligaments, in better contrast
than other tests.
Your doctor may want you to undergo a special kind of MRI called
an MRI arthrogram. For this procedure, your doctor will inject a contrast fluid
into your knee to provide a better view of its structure.
Causes for a Knee MRI
Your doctor may order an MRI scan if they suspect any
abnormalities within your knee joint. The test helps your doctor visualize the
anatomy of your knee to determine the possible cause of your pain,
inflammation, or weakness, without having to do surgery.
According to the Radiological Society
of North America, an MRI is usually ordered to help doctors diagnose and
treat many types of conditions. These include:
- arthritis and other degenerative joint disorders
- bone fractures
- damaged cartilage, ligaments, tendons, or meniscus
- decreased motion of the knee joint
- fluid buildup in the knee
with implanted medical devices
- sports or
Your doctor may order other imaging tests, such as an X-ray,
along with your knee MRI. They could also order an MRI before performing a knee
arthroscopy. This is a minor surgery where a doctor views the inside of your
knee by making a small incision and inserting a scope with a camera.
The Risks of a Knee MRI
Unlike X-rays and CT scans, an MRI does not use radiation. It's
considered a safer alternative for everyone, especially pregnant women. The
radiation levels in CT scans are safe for adults, but they're not safe for
If you have implants containing metal, you face certain risks.
The magnets used in an MRI can cause problems with pacemakers or make implanted
screws or pins shift in the body.
Some people might have an allergic reaction to the contrast dye.
The most common type of contrast dye is gadolinium. According to the
Radiological Society of North America, these allergic reactions are often mild
and easily controlled by medication.
How to Prepare for a Knee MRI
Preparations for an MRI vary between testing facilities. Your
doctor or attending technician will give you complete instructions on how to
prepare for your specific test.
Before your MRI, your doctor will explain the test and do a
complete physical and medical history. Be sure to tell them about any medication
you’re taking, including over-the-counter drugs and herbal supplements. Mention
any known allergies, too. Let them know if you have any implanted medical
devices, because the test can affect them.
Tell your doctor if you’ve had allergic reactions to contrast dye
in the past or if you’ve been diagnosed with kidney problems.
Let your doctor know if you’re pregnant, concerned you may be
pregnant, or breast-feeding. MRIs performed with radioactive contrast dye are
not considered safe for pregnant women. Breast-feeding mothers should stop
breastfeeding for about two days after the test.
The MRI machine is a tight, enclosed space. If you’re
claustrophobic or scared of small spaces, be sure to talk with your doctor
about your options. They may give you a sedative to help relax. In extreme
cases, your doctor may opt for an “open” MRI where the machine is not
as close to your body.
How a Knee MRI Is Performed
Before the scan, you’ll change into a hospital gown and remove
all jewelry and body piercings. If you’re using a contrast dye, an intravenous
line will be inserted into your arm to inject the dye into your bloodstream.
An MRI machine looks like a giant wheel. The center is open so a
flat table can slide in and out of the machine. The rounded, wheel-like part
sends out the magnetic and radio waves used to produce images of your body.
You’ll lie on your back or side on a padded table. The technician
may use pillows or straps to make your knee more comfortable during the test.
This will also help keep your leg still so the machine can take the clearest
The technician will then slide you into the machine feet first.
They’ll tell you when to hold still and hold your breath. These instructions will be given over a microphone,
since the technician will be in a separate room, watching the monitors as they
You won’t feel the machine working, but there may be some loud
noises, such as clacks or thuds, and possibly a whirring noise. The technician
may give you earplugs or provide music.
The test typically takes between 30 minutes to an hour. Once the
right images have been recorded, you’ll be free to change back into your
regular clothes and go about your day.
After a Knee MRI
A radiologist will review your knee MRI scans and give them to
MRI images are black and white. Abnormalities may appear as
bright white spots. These indicate areas where the contrast dye has collected
due to enhanced cell activity.
When your doctor reviews the results, they’ll explain the problem
and go over the next steps for treatment. Depending on your condition,
treatment may require more tests, medication, physical rehabilitation, surgery,
or some combination. Your doctor will help you decide which methods are best