About a thumb CT scan
The thumb has two bones of its own (phalanges) and a long bone in the palm (the first metacarpal), which joins the wrist at the base of the thumb through a saddle-shaped joint (the CMC joint) with the trapezium bone. This joint lets the thumb move in many directions to pinch and grip. A CT (computed tomography) scan uses X-rays and a computer to make detailed cross-section pictures of these small bones, which can be turned into 3D images.
A thumb CT is mainly used to look at the bones, for example:
- fractures at the base of the thumb, such as a Bennett’s fracture (a break into the CMC joint with the joint partly dislocated) or a Rolando fracture (a break into the joint in several pieces), where CT shows the size and position of the pieces and helps plan surgery
- fractures of the trapezium and other small wrist bones nearby
- arthritis at the base of the thumb, including before surgery
- how a fracture is healing, and bone lumps and cysts
For ligament injuries such as skier’s thumb, and for tendons and soft tissue lumps, a thumb MRI or ultrasound is usually better. For the wider hand and wrist, see hand 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 hand by your side. Your hand and thumb rest on a pad and are held still with supports. 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 thumb CT gives a very low dose, because the area scanned is small and 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 thumb CT can help to look at:
- Bennett’s and Rolando fractures
- other fractures of the thumb and nearby wrist bones
- fracture healing
- arthritis at the base of the thumb
- bone spurs, lumps and cysts
- screws and wires after surgery
When to get urgent help: go to A&E or an urgent treatment centre if your thumb looks misshapen after an injury, you cannot move it, or it feels numb, cold or looks pale.
Preparing for your scan
No special preparation is needed, and you can eat and drink normally. Remove rings, 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
Is CT or MRI better for my thumb?
CT is best for the bones, such as fractures at the base of the thumb and arthritis. MRI is better for ligaments, such as skier’s thumb, and tendons. Your referrer will say which is needed; if you are unsure, contact us before booking.
Why do I need a CT if my X-ray showed the fracture?
A CT shows the exact size and position of the broken pieces, especially where the fracture enters the joint. This helps your surgeon decide whether you need an operation and how to do it.
Do I need to choose a side?
Yes. Choose the left or right thumb when you book. If both thumbs need scanning, contact us so the centre can plan the appointment.
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
- Bennett’s fracture management: a systematic review of literature (PMC)
- Osteophyte growth in early thumb carpometacarpal osteoarthritis (PMC)
- NHS – Broken finger or thumb
- NHS – Hand 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.