WEIGHT-BEARING CONE BEAM CT SCANS AND ITS USES IN ANKLE, FOOT, AND KNEE: AN UPDATE ARTICLE

Abstract

Imaging plays a key role in the preoperative diagnosis, surgical planning, and postsurgical assessment of the foot, ankle, and knee pathologies. Interpreting diagnostic imaging accurately is crucial for the clinical practice of orthopedic surgeons. Although among the most used imaging modalities, radiographic assessments are amenable to errors for various technical reasons and superposition of bones. Computed tomography (CT) is a conventional imaging procedure that provides high-resolution images, but fails in considering a truly weight-bearing (WB) condition. In an attempt to overcome this limitation, WB cone beam CT technology has being successfully employed in the clinical practice for the past decade. Besides economically viable and safe, the WB cone beam CT considers WB conditions and provides high-quality scans, thus allowing an equitable and correct interpretation. This review aims to address extensive description and discussion on WBCT, including imaging quality; costs; time consumption; and its applicability in common foot, ankle, and knee, conditions. With this technology increasing popularity, and considering the extensive literature on medical research, radiologists and orthopedic surgeons need to understand its potential applications and use it optimally. Level of Evidence III, Systematic review of level III studies.

Keywords: Ankle Joint; Foot; Knee Joint; Orthopedics; Tomography, X-Ray Computed; Weight-Bearing.

Figure 1. Weight bearing LineUp^® cone-beam computed tomography (CT; CurveBeam, Philadelphia, PA, USA). Patient positioning for ankles and feet scan. The patient stands at the center of the machine, with the X-ray source and image detector at opposing sites. The tube-detector system executes a single rotation around the patient. Curved arrows represent the tube-detector system rotational movement. For knee scanning, the gantry raises to the appropriate level and performs a single rotation (not shown).

Figure 2. Software user interface, Cubevue® (CurveBeam, Warrington, PA, USA) for foot and ankle. The upper-left window represents the volumetric reconstruction, which may be tailored by the user. The remaining windows are multiplanar reconstructions provided by the software. The user can likewise tailor these images and perform measurements.

Figure 3. Foot-Ankle Offset (FAO) measurement using the Torque Ankle Lever Arm System (TALAS^®; CurveBeam, Warrington PA, USA) with Cubevue^® software in a patient with pes planovalgus. In this example, the measured FAO is positive, indicating that the center of the ankle joint is positioned medially to the bisecting line of the foot tripod (valgus alignment). Five points (coordinates) are established using the multiplanar reconstruction - the first metatarsal head WB point (M1), fifth metatarsal head WB point (M5), ground projection of the centermost and highest talus point (T), M1-M5 equidistant point (E), and a CE line point (foot length) crossed by a perpendicular line that includes T. FAO is measured as a percentage of the TF distance divided by the CE distance (foot length). Using this system, FAO measurement is fast and straightforward.