Computed Tomography Scan Architectural Measurements in Adult Foot and Ankle Surgery: A Narrative Review for Orthopaedic Trainees

Abstract

CT scan plays an important role in adult foot and ankle surgery. Plain radiographs are usually the first-line imaging modality for assessing foot and ankle bone and joint architectural abnormalities. However, despite the fact that a CT scan is more expensive and associated with higher radiation exposure, it offers better imaging quality for the assessment of bony lesions in orthopaedics and trauma. Evidence has shown that more accurate measurements can be obtained from a CT scan compared to plain radiographs. Weight-bearing multi-detection CT scanning goes the extra mile by providing a more detailed assessment, especially for intra-articular fractures, and mirrors the real-life foot and ankle dynamics compared to conventional non-weight-bearing CT scans. It also has a relatively lower radiation dose compared to conventional CT scans. CT scan is the best modality for assessing bony lesions whereas MRI is better for soft tissue pathology. An understanding of the role of CT scan in the anatomical assessment of the foot and ankle will help improve communication between orthopaedic surgeons, radiologists, and radiographers. A thorough understanding of when to use a CT scan compared to the other imaging modalities will also lead to better surgical outcomes, reduced cost, and reduced risk from radiation exposure. This review article analyzes the role of CT in assessing relevant radiographic architectural measurements for diagnosis and surgical planning in adult foot and ankle surgery.

Keywords: computed tomography scan; ct scan; foot and ankle surgery; foot deformity; radiological findings; weight-bearing ct.

Figure 1. Image A is a coronal CT scan image with the corresponding axial CT scan in image B showing measurements for the distal tibiofibular syndesmosis at a level 1 cm above the tibial plafond

a: anterior interval; b: posterior interval

Figure 2. The tibiofibular line (TFL)

Image A on the left shows the TFL measurement for a normal ankle while the image B on the right shows an inadequately reduced ankle syndesmosis as evidenced by the TFL

Figure 3. Image A is a sagittal CT image reconstruction with the orange arrow pointing to the intra-articular fracture with depression of the joint surface. The thin yellow line represents the level of the cut for the corresponding axial image on the right. Image B is an axial CT scan showing a displaced intra-articular calcaneal fracture. The green arrows point to the primary fracture line while the blue star represents the superomedial or constant fragment

Figure 4. Three-dimensional reconstructed CT images (panes A, B, D, and E) and sagittal reformatted CT images (panes C and F) showing measurements for (a) hallux-valgus angle, (b) metatarsus adductus angle, (c) effective 1st metatarsal length, (d) intermetatarsal angle for hallux valgus, (e) absolute 1st metatarsal angle, and (f) Meary's angle