CT Scan – Femur (Thigh Bone)

About a CT scan of the femur

The femur (thigh bone) is the longest and strongest bone in the body, running from the hip to the knee. A CT (computed tomography) scan uses X-rays and a computer to make detailed cross-section pictures of the bone, which can be turned into 3D images. CT shows the outer shell (cortex) and inner structure of bone in more detail than any other scan.

A femur CT may be used to look at:

• fractures that are complex or hard to see on X-ray, and how a fracture is healing, including around metalwork or a hip or knee replacement
• bone lumps and lesions, to show their size, shape and effect on the bone, which helps doctors work out what they are likely to be and whether the bone is at risk of breaking
• osteoid osteoma, a small, harmless bone growth that causes pain, often worse at night and eased by anti-inflammatory painkillers, most common in young people; CT is the best scan for finding its small centre
• changes in the shape, length or rotation of the bone, before surgery to correct them

People who have taken bisphosphonate medicines (such as alendronic acid) for osteoporosis for several years have a small risk of an unusual type of thigh bone fracture, known as an atypical femoral fracture. New thigh, hip or groin pain while taking these medicines should be reported to your doctor; X-rays are usually the first test, and MRI or CT may be used if more detail is needed.

For stress fractures, bone bruising and the muscles around the thigh, a femur MRI is usually better. When you book, choose the left or right side.

What happens during the scan

You lie on your back on the scanner bed, usually feet first, with pads to help keep your leg still. The bed moves through a short, open ring while your thigh 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, but may be used to look at a lump or infection; where contrast is needed, it is charged separately.

Is CT safe?

CT uses X-rays, which are a type of ionising radiation. A femur CT gives a relatively low dose, as the thigh contains few organs that are sensitive to radiation. When the top of the femur is scanned, the dose is a little higher because the pelvis is close by. 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.