Differences in Retromalleolar Fibular Groove Morphology According to Level of Axial Computed Tomography Scans

Background: Studies have evaluated types of retromalleolar groove using axial magnetic resonance imaging at the level of 10 mm above the tip of the lateral malleolus. However, no evidence is available to support that this level is appropriate for evaluating retromalleolar groove morphology. Purpose: To assess the influence of the level of axial computed tomography (CT) scans on the assessment of retromalleolar groove morphology. Study Design: Cross-sectional study; Level of evidence, 3. Methods: The study population included 122 patients (mean age, 27.9 +/- 11.8 years; 69 males, 53 female) who underwent CT scans to evaluate foot or ankle pathologies between 2020 and 2023. The shape of the retromalleolar groove (concave, flat, convex, or irregular) at 3 levels of axial CT scans (8, 10, and 12 mm above the tip of the lateral malleolus) was assessed independently by 2 orthopaedic surgeons. The length from the tip of the lateral malleolus to the proximal tip of the fossa of the lateral malleolus was also measured on coronal CT scans. Results: The type of retromalleolar groove was significantly different according to the level of CT scans (8 vs 10 mm, P = .0001; 10 vs 12 mm, P = .0001; 8 vs 12 mm, P = .001). The type of retromalleolar groove was the same at all 3 levels in 31.1% of patients (38/122). The length from the tip of the lateral malleolus to the proximal tip of the fossa of the lateral malleolus was <10 mm in 17.2% of patients (21/122). Conclusion: The shape of the retromalleolar fibular groove was affected by the level at which the CT scan was obtained. Approximately 70% of the patients showed different types of retromalleolar grooves among the 3 CT scan levels.