MRI of the knee: what it shows & what to expect

If you’ve hurt your knee — a twist, a sports injury, or ongoing pain — an MRI is often the scan that gives the clearest answer, because it shows the soft tissues that an X-ray can’t.

What a knee MRI shows

MRI is the best test for the soft tissues of the knee.^[1] It can show:

• Ligaments — including the ACL (anterior cruciate ligament) and other knee ligaments, to detect tears;
• the meniscus — the C-shaped cartilage cushions that commonly tear;
• joint cartilage and signs of arthritis;
• tendons, and problems in the bone like a stress fracture or bruise that an X-ray may miss.

An X-ray is still better for showing the bones themselves, so the two can be complementary.^[2]

What to expect

A knee MRI uses no radiation — just a strong magnet and radio waves.^[2] You lie on the table and your knee is positioned in the scanner (often you don’t go all the way in). It takes about 20–30 minutes, during which you need to stay still so the images aren’t blurred, and you’ll hear the loud knocking that’s normal for MRI (you’ll get ear protection).^[3]

Most knee MRIs need no contrast injection. Occasionally, a special MR arthrogram is done — contrast is injected into the joint first — to look closely at cartilage or after some surgery.

Because of the strong magnet, tell the team about any metal implants or a pacemaker. See our guide on how an MRI works for the basics, and MRI safety for the checks.

Frequently asked questions

Is a knee MRI better than an X-ray?

For soft tissue (ligaments, meniscus, cartilage), yes — MRI shows what an X-ray can’t. For bones alone, an X-ray is quick and often enough. They answer different questions.^[1]

Does a knee MRI hurt or use radiation?

No — it’s painless and uses no radiation. The main things to manage are lying still and the loud noise.^[2]

Do I need contrast for a knee MRI?

Usually not. A contrast injection (or an MR arthrogram into the joint) is only used in specific situations, such as detailed cartilage assessment.^[2]