Knee MRI

You cannot have a knee joint MRI in the following situations:

• If you are pregnant and in the first trimester (unless the pros greatly outweigh the cons)
• If you have any of the following implants: 
• Some older pacemakers and cardiac defibrillators 
• Certain ear implants
• Certain clips used for brain aneurysms
• Certain metal coils placed within blood vessels
• If you have had an artificial joint replacement surgery recently

The doctor may order the scan in the following cases:

• A dead bone is suspected
• An abnormal result on a knee x-ray or bone scan
• Fluid collecting in the knee joint
• Baker’s cyst (a build-up of joint fluid behind the knee)
• Knee cap injury
• Injuries related to sports, such as a sprain or a ligament, tendon or cartilage tear
• Infection of the knee joint
• Arthritis
• Knee pain that does not improve with treatment
• Signs of damage to a knee muscle, cartilage or ligament
• Instability of the knee
• Any complication due to an implant in the knee
• Knee pain with fever
• Knee locking when you walk or move
• To check progress after knee surgery

Consume your food and medicines normally unless specially advised otherwise. Alert your doctor of any allergies you may have. Gadolinium contrast mediums are commonly used for MRIs and are safe to be used in people with an allergy to iodine contrast medium. Tell your doctor if you have had surgery recently or been diagnosed with a serious health problem such as kidney disease. The doctor needs to be informed if you are pregnant or if there is a chance of pregnancy. If you have claustrophobia, your doctor may need to provide a mild sedative before the test. In some cases, like if you fear being in closed spaces, your doctor may advise an “open” MRI, where the machine is not as close to the body.

All accessories and jewellery that contain metal should be taken off before the scan. These include:

• Removable dental work
• Body piercings
• Jewellery, watches, credit cards and hearing aids
• Pens, pocket knives and eyeglasses
• Pins, metal zippers, hairpins and other metallic items
• Mobile phones and tracking devices

Let your doctor know in case you have had any electronic or medical devices implanted in your body, such as pacemakers, artificial valves, stents or brain aneurysm clips as they may affect your test results or be a risk to you. You should also tell your doctor if you have worked with sheet metal as the metal chips may have entered your eye and you may need additional tests to check for this before you undergo an MRI.

(Read more: Swollen knee)

You may be asked to wear a hospital gown or clothes that do not have any metal zips or hooks. Next, you have to lie down on the table that will move into a large scanner. If you require a dye, it may be injected into the vein in your arm or directly into the joint. Images will be taken while the contrast is being injected or after it. The contrast provides better images of the knee joint. Usually, the test lasts from about half an hour to an hour but may take longer. The person performing the scan will observe from another room.

(Read more: Knee sprain)

The MRI is painless but the area to be tested may feel slightly warm. You may feel claustrophobic during the test and may find it tough to remain still. The machine will produce thumping and tapping sounds; you may be provided with earplugs to reduce this noise. 

If your scan requires injecting a contrast medium, you may feel coolness for a minute or so. The injection may cause some discomfort when the needle is inserted. There may be some mild bruising when the needle is removed, and some irritation at the site of IV tube insertion.

Abnormal results may indicate the following:

• Sprain
• Degenerative changes that occur with age
• A tear of knee ligaments
• Fractured bone
• Inflammation
• Osteonecrosis (avascular necrosis)
• Injury of the knee cap
• Bone cancer or tumour
• Osteomyelitis (an infection in the bone)
• Arthritis of the knee
• Baker’s cyst
• Injury in the cartilage or meniscus

Consult with your doctor once you receive the results to know the diagnosis and come up with a treatment plan.

A knee joint MRI has the following benefits:

• It is a non-invasive procedure.
• It involves no exposure to radiation.
• It can produce images of tissues such as tendons, ligaments and muscles from different angles.
• It can detect abnormalities hidden by the bone that cannot be seen on other imaging techniques.

The MRI is considered safe and has minimal risks such as:

• The magnetic field is very strong and may cause implants to malfunction or disturbances in the image.
• If you are given sedation, there may be a risk of its excess use.
• You may have a slight risk of an allergic reaction if a contrast medium is used. In people with severe kidney disease, a rare but serious complication called nephrogenic systemic fibrosis may arise due to the injection of the contrast material gadolinium.

(Read more: Lab tests)

You have no restrictions on your food or driving after the test. However, if you were given a sedative, someone else will need to drive you home.

(Read more: Cracking sound in knee)

Other tests that may be done instead are a CT scan of the knee or an x-ray of the knee.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.