About a shoulder CT scan
The shoulder is a ball-and-socket joint, where the top of the upper arm bone (humerus) sits in a shallow socket (the glenoid) on the shoulder blade. The collarbone joins the shoulder blade at the top of the shoulder. A CT (computed tomography) scan uses X-rays and a computer to make detailed cross-section pictures of these bones, which can be turned into 3D images.
Most shoulder pain, including rotator cuff and labrum problems, is best investigated with a shoulder MRI or ultrasound. A shoulder CT is used when the question is about the bones, for example:
- complex fractures of the top of the humerus, the socket or the shoulder blade, where CT shows how the bone has broken and helps surgeons plan treatment
- recurrent dislocation: each time the shoulder dislocates, it can chip bone from the front of the socket (a bony Bankart lesion) or dent the back of the ball (a Hill-Sachs lesion). 3D CT is the most reliable way to measure this bone loss, which helps surgeons choose the right stabilisation operation
- shoulder replacement: CT shows the shape and angle of the socket and the quality of the bone, and is used to plan the operation and to check a replacement afterwards
- arthritis, fracture healing and bone lumps
If MRI is not possible, a CT arthrogram, with contrast injected into the joint, can be used to look at the labrum and cartilage. You can read more in our article on shoulder 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 arm by your side, and your other arm may be raised above your head to keep it out of the way. Pads are used to help you keep still. The bed moves through a short, open ring while your shoulder is scanned. 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 shoulder CT gives a relatively low dose, although part of the lung and the thyroid are close to the scan area, so the scan is only done when it is likely to help. 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 shoulder CT can help to look at:
- complex fractures of the humerus, socket and shoulder blade
- bone loss after dislocation (bony Bankart and Hill-Sachs lesions)
- planning for stabilisation surgery
- planning and checking shoulder replacements
- osteoarthritis and bone spurs
- fracture healing and bone lumps
When to get urgent help: go to A&E if your shoulder looks misshapen after an injury, you cannot move your arm, or your arm or hand feels numb, tingly or cold. A dislocated shoulder should be put back in place by a professional as soon as possible.
Preparing for your scan
No special preparation is needed, and you can eat and drink normally. Remove necklaces and wear a top 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 shoulder?
MRI is better for most shoulder problems, including rotator cuff and labrum tears. CT is best for the bones, such as complex fractures, bone loss after dislocation and planning shoulder replacements. Your referrer will say which is needed; if you are unsure, contact us before booking.
My shoulder keeps dislocating. Why do I need a CT?
Repeated dislocations can wear away bone from the socket and the ball of the joint. CT measures this bone loss accurately, which helps your surgeon decide which operation will best keep your shoulder stable.
Do I need to choose a side?
Yes. Choose the left or right shoulder when you book. If both shoulders 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
- 3-D CT is the most reliable imaging modality when quantifying glenoid bone loss (PMC)
- Imaging methods for quantifying glenoid and Hill-Sachs bone loss in traumatic instability of the shoulder: a scoping review (PMC)
- Classification and treatment of proximal humerus fractures: agreement across imaging modalities (PMC)
- NHS – Dislocated shoulder
- 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.