About a forearm CT scan
The forearm runs from the elbow to the wrist and contains two long bones, the radius on the thumb side and the ulna on the little-finger side. They are joined at both ends so that the radius can roll around the ulna, letting you turn your palm up and down. 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 forearm CT may be used to look at:
- complex fractures, including fractures of both bones and injuries where one bone breaks and the joint at the elbow or wrist dislocates (Monteggia and Galeazzi injuries)
- how a fracture is healing, and fractures that have not joined (non-union)
- malunion, where a fracture has healed in a bent or twisted position, causing pain or loss of rotation; CT shows the exact angle and twist of the bone, and 3D models made from the scan can be used to plan corrective surgery
- problems with the joints between the two bones at the wrist (the DRUJ) and elbow
- bone lumps, cysts and growths
For muscles, tendons and nerves, such as tendon injuries or nerve compression, a forearm MRI or ultrasound is usually better. For the joints at each end, see elbow CT or wrist CT. When you book, choose the left or right side.
What happens during the scan
Depending on your comfort and the scanner, you either lie on your front with your arm stretched above your head, or on your back with your arm by your side. Pads are used to help you keep your arm still. Sometimes both forearms are scanned so the injured side can be compared with the normal side. If you have a cast or splint, it can usually stay on. 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 forearm CT gives a very low dose, because the area scanned is small and, with the arm positioned away from the body, far from the organs most sensitive to radiation. 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 forearm CT can help to look at:
- complex fractures of the radius and ulna
- fracture healing and non-union
- malunion and planning for corrective surgery
- Monteggia and Galeazzi injuries
- problems with the joints between the forearm bones
- bone lumps, cysts and growths
When to get urgent help: go to A&E if your forearm looks misshapen after an injury, you cannot move your wrist or fingers, or your hand feels numb, cold or looks pale.
Preparing for your scan
No special preparation is needed, and you can eat and drink normally. Remove watches and bracelets before your appointment. 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
Why might both forearms be scanned?
When planning surgery to correct a fracture that has healed in the wrong position, surgeons often compare the injured arm with the normal one. Your surgeon will say if both sides are needed; contact us before booking if so.
Is CT or MRI better for my forearm?
CT is best for the bones, such as fractures and planning surgery. MRI is better for muscles, tendons and nerves. Your referrer will say which is needed; if you are unsure, contact us before booking.
Do I need to choose a side?
Yes. Choose the left or right forearm when you book.
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
- Complex radius shaft malunion: osteotomy with computer-assisted planning (PMC)
- NHS – Broken arm or wrist
- NHS – Elbow and arm pain
- 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.