About a knee MRI scan
The knee is the largest joint in the body. It is held together by four main ligaments – the anterior and posterior cruciate ligaments (ACL and PCL) inside the joint and the medial and lateral collateral ligaments on either side – and cushioned by two C-shaped cartilage pads called the menisci. The kneecap (patella) sits at the front, attached to the thigh muscles and shin bone by strong tendons.
A knee MRI uses a strong magnetic field and radio waves, not X-rays, to show all of these structures. It is the test of choice for a suspected meniscal tear, which may follow a twisting injury in younger people or happen gradually through wear in older adults, and can cause pain, swelling, catching or locking. It also shows ligament injuries such as an ACL tear, which often happens during sport when changing direction or landing, and may cause a “pop”, rapid swelling and the knee giving way. X-rays usually cannot show these soft-tissue injuries.
MRI can also show cartilage damage, bone bruising, arthritis and problems around the kneecap. Left and right knees are separate scans. If you have had previous meniscus surgery, a specialist may request a knee MR arthrogram instead. You can read more in our article on knee MRI.
What happens during the scan
You lie on your back on the scanner bed and go in feet first, so for most people the head stays near the entrance of the scanner. Your knee is placed in a coil, with pads to help keep it still. The scanner is loud, so you will wear ear plugs or headphones, and the radiographer can talk to you throughout. Contrast dye is not usually needed for a knee MRI; where contrast is needed, it is charged separately.
What the scan can show
A knee MRI can help to look at:
- meniscal tears, including bucket-handle and root tears
- ACL, PCL and collateral ligament injuries
- cartilage damage and loose bodies in the joint
- bone bruising and hidden (occult) fractures
- osteoarthritis and inflammatory arthritis
- kneecap problems, including dislocation and patellar tendon injuries
- Baker’s cysts, bursitis and other swellings
- the knee after ligament reconstruction
Preparing for your scan
No special preparation is needed, and you can eat and drink normally. Wear comfortable clothing without metal, such as tracksuit bottoms or shorts. If you have had previous X-rays of your knee or knee surgery, upload the reports or operation notes when you book.
You can usually eat, drink and take your normal medicines unless the scanning centre tells you otherwise. Wear loose, comfortable clothing without metal zips or buttons, and leave jewellery at home. You will be asked to remove metal items such as hair clips, hearing aids, coins and keys, and you may be asked to change into a gown.
Before the scan you will complete a safety questionnaire. Tell the team if you have a pacemaker, any metal implant, surgical clips or other device, if you have kidney problems or allergies, or if you are, or might be, pregnant or breastfeeding. If you feel anxious in enclosed spaces, let us know when you book. Some centres can offer a relaxant, and if you take one you will need someone to take you home and must not drive for 24 hours.
Frequently asked questions
Can a knee MRI show a torn meniscus or ACL?
Yes. MRI is the test of choice for both. It shows whether the meniscus or ligament is torn, the type of tear and any other damage, which helps your doctor plan treatment.
Will I have to go fully into the scanner?
You go in feet first, and the scanner is centred on your knee, so for most people the head stays near the entrance. Many people who are anxious about enclosed spaces find this easier.
Do I need to book the left or right knee?
Yes. Each knee is a separate scan. If you need both, book them together, as two or more areas booked together qualify for the lower clubbed price.
Do I need a referral?
You can tell us if you have a referral from your GP, physiotherapist or consultant and upload it when you book. If you do not have one, select “no referral” when you book and the scanning centre will confirm the next steps with you.
Sources
- Radiopaedia – Meniscal tear
- NHS – Knee ligament surgery
- RadiologyInfo.org – Musculoskeletal MRI
- NHS – MRI scan
The information on this page has been gathered from various sources and is provided for general information only. It is not medical advice. TOP MRI is not liable for the accuracy or completeness of this information. Please speak to your doctor or the scanning centre about your own situation.