About a hip CT scan
The hip is a ball-and-socket joint, where the ball at the top of the thigh bone (the femoral head) sits in a cup-shaped socket in the pelvis (the acetabulum). It carries the weight of the body and allows the leg to move in many directions. A CT (computed tomography) scan uses X-rays and a computer to make detailed cross-section pictures of the bones, which can be turned into 3D images.
A hip CT may be used to look at:
- fractures that are complex, such as fractures of the hip socket, or that cannot be seen on X-ray. NICE recommends MRI first for a suspected hip fracture when X-rays are normal, and CT if MRI cannot be done within 24 hours or is not suitable
- the shape of the hip before surgery, such as in femoroacetabular impingement (FAI), where extra bone on the ball or socket causes pinching and pain, or hip dysplasia, where the socket is too shallow; CT can measure angles and twist (version) of the bones
- hip replacements, to check the position of the parts and look for loosening or bone loss around them, and to plan surgery
- arthritis, bone lumps and cysts, and how a fracture is healing
For the cartilage, labrum, tendons, bursitis, bone bruising and loss of blood supply to the bone (avascular necrosis), a hip MRI or MRI arthrogram of the hip is usually better. You can read more in our article on hip imaging. When you book, choose the left or right side.
What happens during the scan
You lie on your back on the scanner bed with your legs straight, and pads may be used to keep your legs still and turned slightly inwards. The bed moves through a short, open ring while your hip is scanned. For some measurements, the scan also includes your knees. The radiographer controls the scanner from the next room, but can see, hear and talk to you throughout. The scan itself takes only a few minutes. Contrast dye is not usually needed; where contrast is needed, it is charged separately.
Is CT safe?
CT uses X-rays, which are a type of ionising radiation. A hip CT covers part of the pelvis, so the dose is lower than for a full CT of the abdomen and pelvis (about 10 mSv). Because the reproductive organs are close by, the scan is only done when it is likely to help, and centres use low-dose techniques where possible. The risk from a single scan is very small, and every CT scan is checked by a radiologist or radiographer to make sure the benefit of the scan outweighs the risk, as required by the Ionising Radiation (Medical Exposure) Regulations. If you have had other CT scans recently, tell us when you book.
What the scan can show
A hip CT can help to look at:
- complex and hidden hip fractures
- fractures of the hip socket (acetabulum)
- femoroacetabular impingement (FAI)
- hip dysplasia and the angles of the bones
- hip replacement position and loosening
- osteoarthritis and bone spurs
- bone lumps and cysts
When to get urgent help: call 999 or go to A&E if you cannot stand or put weight on your leg after a fall, or if your leg looks shorter or is turned outwards. These can be signs of a broken hip, which usually needs surgery within a day or two. Do not wait for a private scan.
Preparing for your scan
No special preparation is needed, and you can eat and drink normally. Wear clothing without metal, or you may be asked to change into a gown. Upload any previous X-ray or scan reports and letters from your surgeon when you book, and remember to choose the correct side.
Wear loose, comfortable clothing without metal zips, poppers or buttons, and leave jewellery at home, as metal in the scan area can affect the pictures. You may be asked to change into a gown. Unlike MRI, CT is not affected by pacemakers or most metal implants, and the scanner is a short open ring rather than a tunnel, so it is usually easier for people who feel anxious in enclosed spaces.
Tell the team before your scan if you are, or might be, pregnant or breastfeeding, if you have kidney problems, diabetes (especially if you take metformin), asthma, thyroid problems or allergies, or if you have had a reaction to contrast dye before. If you need contrast, you may be asked for a recent kidney blood test result.
Frequently asked questions
Is CT or MRI better for my hip?
CT is best for the bones, such as fractures, the shape of the hip and joint replacements. MRI is better for cartilage, the labrum, tendons and bone bruising. Your referrer will say which is needed; if you are unsure, contact us before booking.
I have a hip replacement. Can I have a CT?
Yes. CT is often used to check hip replacements, and modern scanners use techniques to reduce the effect of the metal on the pictures. Tell us about your implant when you book.
Do I need to choose a side?
Yes. Choose the left or right hip when you book. Some scans for impingement or dysplasia include both hips; contact us if your surgeon has asked for both.
Do I need a referral?
Because CT uses radiation, each scan has to be justified by a qualified professional before it can go ahead. Upload a referral from your GP or consultant when you book if you have one. If you do not, select “no referral” and the scanning centre will review your request and confirm the next steps with you, which may include arranging a referral.
Sources
- NICE CG124 – Hip fracture: management
- The use of computed tomography in identifying radiologically occult hip fractures in the elderly (PMC)
- NHS – Hip pain
- NHS – Broken hip
- NHS – CT scan
- UKHSA – Patient dose information: guidance
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.