MRI of the hip: what it shows, how it works and what to expect

An MRI scan takes detailed pictures of the inside of the body. The NHS says it is used to help diagnose conditions, plan treatment and check how well treatment is working. For the hip, the scanner is a large machine with a short tunnel through it and a flat bed that moves through the scanner. You lie still while images are taken of the hip joint and the structures around it.

Versus Arthritis describes the hip tests in order. X-rays are often the best way to find out what is wrong because they show bone condition. CT can be helpful where the hip has an unusual shape, such as a very shallow socket. MRI uses radio waves to build a picture of the soft tissue, such as the muscles and tendons, inside the hip. That is why it is typically requested when the X-ray is normal or does not explain the pain.

The main strength of MRI is soft tissue and bone marrow detail. Versus Arthritis singles out avascular necrosis, a painful condition in which the blood flow to the ends of the bone is reduced and the bone collapses, as one condition for which MRI is particularly helpful. The same charity lists other hip problems that can cause pain, including tendon problems such as snapping iliopsoas tendon, and the NHS lists sprain or strain and tendonitis, osteoarthritis, bursitis, hip fracture and joint infection among the common causes of hip pain.

An MRI may therefore be asked for when a doctor wants to look at tendons, bursae, the joint lining, or the bone marrow. It is not needed for every hip complaint. The NHS says that treatment depends on the cause and that a specialist may do a scan and discuss treatments such as surgery.

• Pain that has not settled with treatment and where the X-ray is normal.

• Suspected avascular necrosis.

• Soft tissue problems such as tendon injuries or bursitis.

• Planning before surgery, as requested by a specialist.

The NHS says the hospital will tell you if there is anything you need to do beforehand. You may be asked not to wear anything with metal in it, such as jewellery, a bra, hair clips or hearing aids, to remove coins and keys, and to change into a hospital gown if your clothes have metal parts. You will be asked to fill in a form asking whether you are pregnant, breastfeeding, have had surgery, have kidney problems, have metal parts in your body such as surgical clips, a pacemaker or dental fillings, or have allergies including to contrast dye.

Not everyone can have an MRI. An NHS leaflet for MRI arthrograms lists items that need checking, such as cardiac pacemakers, prosthetic heart valves, neurostimulators, aneurysm clips, ear implants, metal fragments in the eye and some piercings, and asks you to telephone the MRI unit before your appointment if any apply. If you have a hip replacement or any other implant, declare it on the form; the radiographer will advise whether the scan can go ahead.

According to the NHS, you will be asked to lie flat on the bed, given ear plugs or headphones because the scanner makes loud bangs and clicks, and need to lie still so the images are clear. The radiographer controls the scanner from another room and can hear and speak to you. You may be given an injection of contrast medium, or dye, to help show more detail in some scans.

If you have an MRI arthrogram, the Lincolnshire leaflet explains that a dye is injected into the joint under X-ray guidance, using local anaesthetic on the skin, before you go to the MRI scanner, and that the whole procedure can take up to 1.5 hours with the scan itself taking around 20 minutes. Afterwards the joint may feel stiff and swollen and you may hear crackling for up to 48 hours, and the leaflet recommends not driving for 24 hours and seeking advice from your GP or A&E if the joint becomes painful, inflamed or red.

If you are anxious or claustrophobic, the NHS suggests talking to a healthcare professional before the appointment, as you may be able to have a medicine to help you relax, and you can ask to bring someone to support you. If you have a sedative, you will need someone to take you home and should not drive for 24 hours.

The radiographer will not be able to tell you the result on the day. The NHS says the images need to be looked at by a radiologist, who writes to the doctor who referred you, and that it usually takes 1 to 2 weeks. You may need a follow-up appointment to discuss the results, and if you have heard nothing after a few weeks you should contact the doctor who referred you.

The result will be interpreted alongside your symptoms and examination. The report is only one part of the picture. Your doctor will explain what it means and what comes next, which could include physiotherapy, injections, further tests or referral to an orthopaedic specialist.

The NHS says that in many areas you may be able to get help from NHS community musculoskeletal (MSK) services without a GP referral, and that a specialist may arrange a scan. Private MRI is also available in the UK. The safety checks are similar, and in either setting the result should be reviewed by a clinician who can examine you.