A weight-bearing computed tomography (WBCT) scan captures detailed, three-dimensional pictures of the foot, ankle, or knee while a person is standing in a natural position. Unlike a traditional CT scan performed while lying down, this technology reveals how the anatomy functions under the body’s load. A computer combines a series of X-ray images taken from various angles to create cross-sectional views of bones, joints, and soft tissues.
The Purpose of Weight Bearing Imaging
Imaging under a load is performed to observe the body’s true biomechanics in a functional state. When you stand, the alignment of your bones and the spaces within your joints change significantly compared to when you are lying down. Capturing images in this loaded state provides an accurate representation of what causes pain or instability during daily activities, allowing physicians to assess the alignment and stability of the foot and ankle as they support the body.
This concept is similar to a mechanic checking a car’s alignment. The assessment is most accurate when the car is on the ground, with its full weight on the tires, not when it is on a lift. A non-weight-bearing image might show that bones appear perfectly aligned, but this can be misleading. Under the body’s weight, a subtle instability, a collapsing arch, or abnormal joint spacing may become apparent that would otherwise be hidden.
This functional information is valuable for diagnosis and treatment planning. By accurately measuring joint angles, positions, and the space between bones under load, specialists can identify structural issues contributing to a patient’s symptoms. This detailed view helps create more effective and personalized treatment plans.
The Weight Bearing CT Procedure
Getting a weight-bearing CT scan is a straightforward and quick process. Upon arriving, you may be asked to change into a gown and will need to remove shoes, socks, and any metal objects from your lower extremities, such as ankle bracelets. The WBCT machine is different from a traditional, tunnel-like scanner, consisting of a circular platform for you to stand on and a gantry, or ring, that moves around your lower legs.
A technologist will guide you to step onto the platform, often marked with circles for foot placement, and ask you to stand naturally, holding onto handles for stability. You must remain as still as possible while the gantry rotates around your feet and ankles. This ensures the captured images are clear and accurate.
The scan itself takes less than one minute. Afterward, a technologist processes the images to create the 3D models for the doctor’s review. The scanner’s open design and short duration reduce feelings of claustrophobia. The radiation exposure is low, comparable to standard foot and ankle X-rays.
Conditions Diagnosed with Weight Bearing CT
Weight-bearing CT scans are used to evaluate complex orthopedic conditions where body weight is a factor. The 3D models created from the scan help surgeons plan procedures with greater precision and later verify that a correction has been successful. Common conditions diagnosed or assessed with a WBCT include:
- Flatfoot deformity (pes planus), to demonstrate the collapse of the foot’s arch under load.
- Bunions (hallux valgus), to reveal the true extent of the deformity and bone rotation for surgical planning.
- Arthritis, by showing the actual narrowing of joint spaces when a person is standing.
- Ankle instability or syndesmotic sprains (a high ankle sprain), by revealing abnormal movement between bones that only occurs under weight.
- Tarsal coalitions, which are abnormal connections between bones in the back of the foot.
- Subtle fractures that are not visible on standard X-rays.
This technology is effective at identifying issues that may be missed with other imaging methods.
Comparison with Other Imaging Techniques
A WBCT scan combines three-dimensional detail with functional positioning. Compared to a traditional CT scan, the primary difference is the element of load. A traditional CT provides excellent bone detail but is performed while the patient is lying down, which does not show how bones and joints align under the stress of standing.
Standard X-rays can be taken while standing, but they are limited to two-dimensional images. This 2D perspective can cause anatomical structures to overlap, hiding the true nature of a 3D deformity. A WBCT scan overcomes this by creating detailed cross-sectional images that can be viewed from any angle without obstruction.
Magnetic Resonance Imaging (MRI) is the preferred method for visualizing soft tissues like ligaments and tendons in high detail. However, MRI scans are performed with the patient lying down and are less effective for assessing bone alignment. While a WBCT scan can visualize soft tissues, its strength is providing detailed images of bony anatomy in a functional, weight-bearing state.