A knee MRI (magnetic resonance imaging) scan is a imaging method that uses powerful magnets and radio waves to create pictures of the knee joint and surrounding muscles and other tissues.
See also: Leg MRI
An MRI does not use radiation. Single MRI images are called slices. The images can be stored on a computer or printed on film. One exam produces dozens or sometimes hundreds of images.
MRI - knee
You may be asked to wear a hospital gown or clothing without metal fasteners (such as sweatpants and a t-shirt). Certain types of metal can cause blurry images.
You will lie on a narrow table, which slides into a large tunnel-like tube.
Some exams require a special dye (contrast). The dye is usually given before the test through a vein (IV) in your hand or forearm. Sometimes, the dye is given directly into a joint. The dye helps the radiologist see certain areas more clearly.
During the MRI, the person who operates the machine will watch you from another room. The test most often lasts 30-60 minutes, but may take longer.
You may be asked not to eat or drink anything for 4 - 6 hours before the scan.
Tell your doctor if you are afraid of close spaces (have claustrophobia). You may be given a medicine to help you feel sleepy and less anxious, or your doctor may suggest an "open" MRI, in which the machine is not as close to the body.
Before the test, tell your health care provider if you have:
Because the MRI contains strong magnets, metal objects are not allowed into the room with the MRI scanner:
An MRI exam causes no pain. If you have difficulty lying still or are very nervous, you may be given a medicine to relax you. Too much movement can blur MRI images and cause errors.
The table may be hard or cold, but you can request a blanket or pillow. The machine produces loud thumping and humming noises when turned on. You can wear ear plugs to help reduce the noise.
An intercom in the room allows you to speak to someone at any time. Some MRIs have televisions and special headphones that you can use to help the time pass.
There is no recovery time, unless you were given a medicine to relax. After an MRI scan, you can resume your normal diet, activity, and medications.
Your doctor may order this test if you have:
Your doctor may also order this test to monitor your progress after knee surgery.
A normal result means your knee appears normal.
Abnormal results may be due to a sprain or tear of the ligaments in the knee area, including:
Abnormal results may also be due to:
Consult your health care provider with any questions and concerns.
MRI contains no radiation. To date, no side effects from the magnetic fields and radio waves have been reported.
The most common type of contrast (dye) used is gadolinium. It is very safe. Allergic reactions to the substance rarely occur. However, gadolinium can be harmful to patients with kidney problems who require dialysis. If you have kidney problems, please tell your health care provider before the test.
The strong magnetic fields created during an MRI can cause heart pacemakers and other implants to not work as well. It can also cause a piece of metal inside your body to move or shift.
Tests that may be done instead of a knee MRI include:
Wilkinson ID, Paley MNJ. Magnetic resonance imaging: basic principles. In: Grainger RC, Allison D, Adam, Dixon AK, eds. Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 5.
DeLee JC, Drez D Jr, Miller MD, eds. DeLee and Drez’s Orthopaedic Sports Medicine. 3rd ed. Philadelphia, Pa: Saunders Elsevier; 2009:chap 23.
Grainger RG, Thomsen HS, Morcos SK, Koh DM, Roditi G. Intravascular contrast media for radiology, CT, and MRI. In: Adam A, Dixon AK, eds. Grainger & Allison's Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 2.