Weight-bearing computed tomography (WBCT), also called weight-bearing cone-beam CT or standing CT, is a medical imaging technique in which cone-beam computed tomography of the lower limb is acquired while the patient stands, so that the bones are imaged under physiological load. It is used mainly in foot and ankle surgery and, less commonly, for the knee. Its stated advantage over conventional computed tomography is that it combines three-dimensional imaging with the loaded position that conventional radiography provides only in two dimensions.

The equipment used is a dedicated extremity cone-beam scanner. Compared with multidetector CT, it delivers a lower radiation dose, acquires images in less time, costs less to install and is compact enough for use at the point of care. These properties apply to non-weight-bearing examinations of the upper limb as well.

The technique emerged in the 2010s and has been studied most extensively in progressive collapsing foot deformity, hallux valgus, syndesmotic injury and hindfoot alignment. Its evidence base is large but of limited methodological quality, and several studies have found no advantage over conventional CT or weight-bearing radiographs for particular measurements. Adoption remains partial: a 2025 survey of the American Orthopaedic Foot and Ankle Society found that 42% of responding members had access to a scanner. Much of the field's leading literature is produced by authors with disclosed financial relationships to scanner manufacturers.

Principles and technique

WBCT uses cone-beam geometry, in which a cone-shaped X-ray beam and a flat-panel detector rotate around the limb, rather than the fan-beam geometry and rotating detector array of conventional multidetector CT. Cone-beam acquisition allows a compact gantry that the patient can step into, and produces isotropic voxels suitable for multiplanar and three-dimensional reconstruction.

Dedicated extremity cone-beam scanners are small enough to sit in an outpatient clinic and, in some designs, to run from a standard mains outlet with minimal additional shielding. Depending on the device, one or both limbs may be scanned from below the heel to above the knee.

Relationship to extremity cone-beam CT

Although the modality is named after its weight-bearing capability, the underlying technology is extremity cone-beam CT, and several of its practical advantages are properties of that technology rather than of loading. Reviews of musculoskeletal cone-beam CT describe reduced radiation dose, short acquisition times, low equipment cost and a footprint small enough for point-of-care use in a clinic or emergency department. These characteristics apply equally to acquisitions made without load.

A single acquisition yields both the loaded alignment information conventionally obtained from weight-bearing radiographs and the three-dimensional detail conventionally obtained from CT. Proponents argue that this allows one examination to replace two, shortening the diagnostic pathway; a single-centre series of 11,009 scans reported a 77% reduction in acquisition time relative to the imaging it displaced.

The same class of scanner is accordingly used for regions that cannot be loaded. Cone-beam CT has been evaluated for trauma of the small bones and joints, and a meta-analysis of diagnostic test accuracy found it useful in radiocarpal fractures. A scoping review of musculoskeletal trauma imaging concluded that image quality was high and dose lower than multidetector CT, while noting limited evidence on cost-effectiveness. In children, the dose and cost advantages have been reported independently of any weight-bearing indication.

Reported disadvantages of cone-beam geometry include increased scatter, cone-beam artefact, and poorer soft-tissue contrast than multidetector CT. An assessment of image quality in a dedicated extremity cone-beam system found bone visualisation comparable to multidetector CT but soft-tissue performance inferior. The American College of Radiology notes that the soft-tissue contrast of WBCT "is relatively poor, making it difficult to detect associated periarticular abnormalities such as soft tissue swelling, effusions, fluid collections, and muscle atrophy".

Motion artefact from postural sway during standing acquisition is a recognised problem, and dedicated motion-compensation algorithms have been developed for extremity and weight-bearing knee imaging. Where a large field of view is obtained by stitching successive acquisitions, geometrical stitching errors have been documented as a further source of measurement inaccuracy.

Radiation dose

Radiation dose is generally lower than conventional CT of the same region but higher than radiography. A 2024 systematic review of 21 studies by an NHS medical-physics and radiography group found that musculoskeletal cone-beam CT reduced effective dose relative to multidetector CT by a mean factor of about 12, while digital radiography delivered roughly 4.55 times less dose than cone-beam CT. In a paediatric series, mean dose was 0.63–1.1 mGy with WBCT compared with 7.92–10.37 mGy with non-weight-bearing CT. A single-centre review of 11,009 scans reported a small reduction in effective dose (4.3 versus 4.8 μSv) together with a 77% reduction in acquisition time; the same paper reported an institutional financial benefit, and its authors disclose shareholdings in a scanner manufacturer.

History

Cone-beam CT was established in dental and maxillofacial imaging before being applied to the extremities. Weight-bearing CT of the lower limb was described by a Finnish group in 2013. Early orthopaedic validation work reported that standing cone-beam CT allowed more accurate measurement of bone position than radiographs or conventional CT.

Swiss investigators independently applied the technique to the subtalar joint in 2014, and a radiology group at the Balgrist University Hospital in Zurich published comparisons of the hindfoot and later the knee between non-weight-bearing and upright positions in 2014 and 2015. An international study group was formed to coordinate research, later becoming the International Weight Bearing CT Society, and a dedicated textbook appeared in 2020. A 2024 scoping review identified 129 studies published between 2013 and 2023, of which 84% concerned the foot and ankle.

Measurement methods

WBCT is used less for the detection of lesions than for measurement of three-dimensional alignment, and a number of quantitative methods have been developed.

The foot and ankle offset (FAO) expresses hindfoot alignment as a percentage derived from the three-dimensional positions of the calcaneus, the metatarsal heads and the ankle joint. Reported mean values are approximately 2.3% in normal feet, −11.6% in varus and 11.4% in valgus, with high intra- and inter-observer reliability. A later prospective study of 250 feet proposed a normal range of −1.64% to 2.71%.

Distance and coverage mapping render the separation between two articular surfaces as a colour map, and have been applied to the subtalar, Chopart and ankle joints. Applied to the ankle, three-dimensional joint-space mapping achieved a smallest detectable difference of about 0.15 mm, although the authors described standardisation as unresolved. Semi-automated segmentation and statistical shape modelling have also been used, and automated syndesmosis measurement has been reported to agree with manual measurement to within 2.7° and 0.5 mm.

A 2025 international task force proposed standardised conventions for three-dimensional foot and ankle measurement, reflecting continuing heterogeneity of method between centres.

Clinical applications

Progressive collapsing foot deformity

The largest body of WBCT research concerns progressive collapsing foot deformity (formerly adult acquired flatfoot). Subluxation of the middle facet of the subtalar joint can be measured with high reliability and has been proposed as a marker of peritalar subluxation. Coverage mapping has been used to quantify uncovering of the talar head. A prospective series of 26 patients reported that surgical correction improved both WBCT measurements and patient-reported outcomes. An expert consensus statement recommends assessment of sinus tarsi and subfibular impingement and of posterior facet subluxation.

WBCT has also revised earlier estimates derived from radiography: measuring the sinus tarsi directly, one series found bony subfibular impingement in flatfoot to be less common than had previously been reported.

Evidence in this area is not uniformly favourable. A study comparing WBCT with MRI concluded that the association between WBCT three-dimensional measurements and ligament or tendon tears was limited. Another found that talocalcaneal overlap did not differ significantly between weight-bearing radiographs and WBCT.

Hindfoot alignment and ankle osteoarthritis

WBCT has been used to measure hindfoot alignment, and the ACR notes that hindfoot alignment view radiographs overestimated varus alignment by 3.9 mm compared with WBCT. Reliability depends heavily on which anatomical landmarks are chosen: a five-rater study found good agreement for methods based on the heel contact point but poor agreement for methods using the calcaneal wall, and only weak correlation between radiographic and cone-beam measurements. A comparison of six published three-dimensional methods found that they do not agree well with one another. Subtalar alignment has been studied in ankle osteoarthritis, where more valgus subtalar alignment was found in varus ankle osteoarthritis, without differences across osteoarthritis stages.

Syndesmotic and ankle injury

Reference values for the normal tibiofibular syndesmosis in 200 ankles have been published. A systematic review and meta-analysis of 11 studies and 559 ankles concluded that WBCT "has the potential" to differentiate stable from unstable syndesmotic injury, language the authors deliberately hedged. That review prompted a published exchange: trauma surgeons from Munich and Amsterdam wrote to the journal disputing its methods and conclusions, while an invited commentary from a proponent of the technique argued the opposite.

This debate concerns unstressed standing acquisition. Subtle syndesmotic instability may not be apparent under body weight alone, and adding an external rotation torque to the loaded ankle has been reported to improve detection. A 2025 systematic review examined external torque application during syndesmotic assessment across imaging modalities. Axial loading with the foot in different positions has been studied using conventional CT for the same purpose. An Asia-Pacific society consensus statement on chronic syndesmotic injury addresses WBCT among the available imaging options.

Midfoot and Lisfranc injury

Volumetric WBCT measurement has been reported to detect subtle Lisfranc instability with high sensitivity and specificity. A cadaveric study found an asymmetric "lambda sign" in 83.3% of specimens under full weight-bearing versus 33.3% without load. However, a 2026 systematic review and meta-analysis found no significant difference between conventional CT and WBCT for the principal linear measurements, with WBCT superior only for selected parameters such as axial joint volume. A study defining normal values concluded that the Lisfranc joint "is rigid with little to no physiologic widening".

Hallux valgus

WBCT has been used to assess pronation of the first metatarsal and instability of the first tarsometatarsal joint. A 2026 systematic review of 14 studies and 706 feet found that WBCT outperformed radiographs for measuring pronation but that "its clinical impact remains uncertain".

Knee