Preparing for a knee MRI is straightforward. Most knee scans require no fasting, no injections, and no special preparation beyond wearing the right clothes and disclosing any metal in your body. The scan itself typically takes about 11 minutes, and you can walk out and resume normal activities immediately afterward. Here’s what to know before your appointment.
What to Wear (and What to Avoid)
The simplest thing you can do is dress in comfortable clothes with no metal. That means no zippers, snaps, hooks, or underwire bras. Sweatpants and a cotton t-shirt work well. Skip anything with metallic threads, which are more common than you might think. Many athletic and “tech” clothing brands now weave silver or copper microfibers into fabrics for odor control or antibacterial properties. These invisible metal threads can heat up inside the MRI and cause skin burns. A case published in the American Journal of Neuroradiology documented exactly this: a patient was burned by silver-embedded microfibers in an undershirt that looked and felt completely normal.
Many imaging centers will ask you to change into a hospital gown regardless of what you’re wearing. If they don’t, you’ll still need to remove anything with metal, including belts, jewelry, watches, hair clips, and body piercings. Leave valuables at home or in a locker if one is provided.
Eating, Drinking, and Medications
For a standard knee MRI without contrast, there are no dietary restrictions. Eat and drink normally, and take your regular medications as usual. If your scan requires an intravenous contrast agent (a substance injected into your arm to make certain structures show up more clearly), you may be asked to avoid solid food for four to eight hours beforehand. Your scheduling team will tell you in advance if contrast is part of your exam.
The Metal Screening Process
Before you enter the scan room, you’ll fill out a safety questionnaire about metal inside your body. MRI uses an extremely powerful magnet, and certain implants or metal fragments can move, malfunction, or heat up during the scan. Be ready to answer questions about:
- Cardiac devices such as pacemakers or defibrillators, which are typically not safe in a standard MRI
- Surgical hardware including joint replacements, screws, plates, rods, or surgical clips
- Other implants such as cochlear implants, drug infusion pumps, neurostimulators, or IUDs
- Metal fragments from previous injuries (bullets, shrapnel) or occupational exposure (welding, metalwork)
Joint replacements are generally safe for MRI but need to be documented so the technologist can verify. If you’ve ever had metal fragments near your eyes, from welding without eye protection for instance, you may need an X-ray of your eye sockets before the scan can proceed. If you have any implant and aren’t sure of the brand or model, mention this when you schedule so the facility can research it ahead of time.
Tattoos and MRI
If you have tattoos, especially large ones with black ink or designs featuring loops and circular patterns, let the technologist know. Some tattoo inks contain iron oxide, which can heat up during the scan and cause a burning or stinging sensation at the tattoo site. The risk is low, but the fix is simple: the technologist can place a cold, wet washcloth over the tattoo before the scan starts. If you feel any warmth or tingling at a tattoo during the procedure, tell the technologist immediately through the intercom.
If You Get Anxious in Tight Spaces
MRI machines are enclosed tubes, and the experience involves loud banging and clicking noises for the duration of the scan. For a knee MRI, your knee goes into the center of the machine, but depending on your height, your head and upper body may remain near or partially outside the opening. This makes it more tolerable than a head or chest MRI for many people.
If you know you’re claustrophobic, call the facility before your appointment. Many centers offer mild sedation, typically a pill or inhaled gas that reduces anxiety while keeping you awake. Nitrous oxide (the same gas used in dental offices) works quickly, wears off fast, and doesn’t require needles. If you receive any form of sedation, you’ll need someone to drive you home. Some facilities also have open or wide-bore MRI machines that feel less confining.
You’ll be given earplugs or headphones to dampen the noise. Some centers let you listen to music during the scan.
What Happens During the Scan
You’ll lie on your back on a padded table. The technologist will position your knee with a slight bend of about 15 degrees and place a specialized coil around it. This coil looks like a molded plastic cradle and is what captures the images. It doesn’t hurt or squeeze. Once positioned, the table slides into the MRI tube.
The most important thing you’ll need to do is hold still. Even small movements blur the images and may mean repeating a sequence. A standard knee MRI takes about 11 minutes of actual scanning time, though you should plan to be at the facility for 30 to 45 minutes total once you account for check-in, changing, and screening. You’ll hear a series of loud knocking, buzzing, and humming sounds as different image sequences run. Each sequence lasts a few minutes, and there are brief pauses between them.
You’ll have a call button or squeeze ball to signal the technologist at any time, and they can talk to you through a speaker in the machine.
Contrast Injections for Knee MRI
Most routine knee MRIs don’t use contrast. But if your doctor is looking for specific types of damage, infection, or tumors, they may order contrast. There are two types you might encounter.
Intravenous contrast involves a small needle in your arm. The substance (a gadolinium-based agent) travels through your bloodstream and highlights areas of inflammation or abnormal tissue. Your kidneys filter it out within hours. If you have kidney problems, the facility will likely require a blood test beforehand to confirm your kidneys can handle it safely. People with severe kidney disease face a small risk of a tissue disorder from gadolinium, so the imaging team screens for this carefully.
An MR arthrogram is different. A doctor injects contrast material directly into your knee joint before the MRI, which gives a much more detailed look at cartilage, ligaments, and the meniscus. This is less common and involves a separate procedure before you enter the scanner.
After the Scan
If you had a standard knee MRI without sedation, there are no restrictions. You can drive yourself home, go back to work, exercise, and eat normally. If contrast was used, drinking extra water helps your kidneys flush it out faster. If you received sedation, plan to rest for the remainder of the day and don’t drive until the effects have fully worn off.
Results typically go to your referring doctor within a few business days, though some facilities offer faster turnaround. The scan itself is painless, and the only discomfort most people report is stiffness from lying still.