MRI or CT scan for my knee: what is the difference, and why was I sent for one?

The short verdict

Neither scan is simply better. They answer different questions. If your surgeon suspects a torn ligament or meniscus, a cartilage injury or a bone bruise, MRI is normally the right test. If the concern is the exact shape of a fracture, how well a bone has healed, or the position of bones and tunnels before surgery, CT is often more useful. An ordinary X-ray usually comes first for both.

How they compare

• Shows well: MRI shows ligaments, tendons, meniscus, cartilage, bone bruising and fluid; CT shows bone edges, fragments and alignment
• Radiation: MRI uses magnets and none; CT uses X-rays, at a higher dose than a plain X-ray
• Time in the scanner: a knee MRI often takes around 20 to 40 minutes; a CT is usually a few minutes
• Noise and space: MRI is noisy and some people find the tunnel enclosed; CT is quick and more open
• Metal: some implants or devices rule out MRI or blur the images; CT copes better with metal, though it can also cause artefact
• Typical uses: MRI for sports injuries and unexplained pain; CT for tibial plateau fractures, revision ACL tunnel planning, kneecap alignment measurements and some knee replacement problems

Who each scan tends to suit

MRI tends to suit someone with a twisting injury, swelling, locking or giving way, or ongoing pain with a normal X-ray. CT tends to suit someone with a fracture that needs planning, a previous ACL reconstruction being considered for revision, a kneecap that keeps dislocating where bone shape is being measured, or a person who cannot have MRI because of a pacemaker or certain metal implants.

When to see a knee surgeon in Doha

If you have been told you need a scan, or you already have one and are unsure what it means, an examination helps put the images in context. Scan findings must always be matched to your symptoms and examination. Dr. Gelber at Aman Hospital can review existing images, decide whether another scan would change your treatment, and avoid tests that would not.