About a knee MR arthrogram
Most knee problems can be assessed with a standard MRI scan. An MR arthrogram is a specialist scan used when more detail is needed. Contrast dye is injected into the knee before the MRI, which fills the joint and outlines the menisci (the two C-shaped cartilage cushions between the thigh and shin bones), the joint cartilage and the ligaments.
It is used most often after knee surgery. Once a meniscus has been repaired, or part of it has been removed (partial meniscectomy), scar tissue and healing changes can look like a tear on a standard MRI. Dye that seeps into a gap in the meniscus helps the radiologist tell a new or recurrent tear apart from healed tissue. Studies have found MR arthrography to be more accurate than standard MRI for recurrent meniscal tears after a repair or after a larger part of the meniscus has been removed. Left and right knees are separate scans.
What happens during the scan
An MR arthrogram is done in two parts. First, a small amount of contrast dye (gadolinium) is injected directly into the knee joint. The skin is cleaned and numbed with local anaesthetic, and the needle is guided into the joint using X-ray (fluoroscopy) or ultrasound. You may feel a sharp scratch, some pressure and a feeling of fullness in the joint, but it should not be painful. You will then be asked to move the joint gently to spread the dye.
Shortly afterwards you have the MRI scan. You lie still on the scanner bed with the knee in a coil while the pictures are taken; the scan itself usually takes about 20–40 minutes. The scanner is loud, so you will wear ear plugs or headphones, and the radiographer can talk to you throughout. Allow up to 1½ hours for the whole appointment.
Referral needed: this scan requires a referral from a specialist, such as an orthopaedic surgeon, sports medicine doctor or specialist physiotherapist. You can upload the referral when you book.
What the scan can show
A knee MR arthrogram can help to look at:
- new or recurrent meniscal tears after a meniscus repair or partial meniscectomy
- whether a meniscus repair has healed
- damage to the joint cartilage, including cartilage repairs
- loose pieces of cartilage or bone inside the joint
- ligament problems, including after reconstruction surgery
- persistent, unexplained knee pain when a standard MRI has not given an answer
Preparing for your scan
No special preparation is usually needed, and you can eat and drink normally. Because the injection goes into a joint, tell us when booking if you take blood-thinning medicines, have a skin infection near the joint, have kidney problems or have had a reaction to contrast dye. Arrange for someone else to drive you home, as you should not drive for 24 hours afterwards.
If you have had knee surgery, bring or upload your operation notes or previous scan reports if you have them, as these help the radiologist interpret the pictures.
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.
After the arthrogram
The joint may feel stiff, swollen or full, and you may hear it creak or gurgle as you move it. This usually settles within 48 hours. Keep the joint moving gently, but avoid vigorous exercise for at least 24 hours. An ice pack and a simple painkiller can help. Do not drive for 24 hours after the injection. Contact your GP or NHS 111 if the joint becomes increasingly painful, red, hot or swollen, or if you develop a fever, as infection, although rare, needs prompt treatment.
Frequently asked questions
Do I need a referral for an MR arthrogram of the knee?
Yes. This scan requires a referral from a specialist. Please upload your referral when you book so the scanning centre can check that an arthrogram is the right test for you.
What is the difference between an MRI and an MR arthrogram?
A standard MRI is taken without anything being injected into the joint. In an MR arthrogram, contrast dye is injected into the joint first. The dye fills the joint and outlines the cartilage, ligaments and other structures, which can show small tears that a standard MRI may not.
Is the injection painful?
The skin is numbed with local anaesthetic first, so most people feel only a sharp scratch and some pressure. The joint may feel full or stiff for a day or two afterwards.
Can I drive home afterwards?
No. You should not drive for 24 hours after the injection, so please arrange for someone to take you home.
Why might I need an arthrogram rather than a standard knee MRI?
After meniscus surgery, healed tissue can look similar to a tear on a standard MRI. The contrast dye in an arthrogram helps show whether there is a genuine new tear. Your specialist will advise whether you need a standard MRI or an arthrogram.
Sources
- RadiologyInfo.org – Arthrography
- United Lincolnshire Hospitals NHS – MRI Arthrogram
- Imaging the postoperative knee meniscus: an evidence-based review (American Journal of Roentgenology, 2018)
- Radiology (RSNA, 2003) – MR arthrography of the postoperative meniscus
- 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.