Fibular Length and Syndesmotic Width Variations in Ankle Osteoarthritis: A Weightbearing CT Analysis of Coronal Plane Deformities.

Background: The relationship between fibular morphology, syndesmotic anatomy, and coronal plane deformities in ankle osteoarthritis (OA) remains poorly understood. Whether fibular length and syndesmosis width vary with different alignment patterns is unknown. This study aimed to evaluate these structural parameters in OA patients compared to normal controls using weightbearing computed tomography (WBCT).

Methods: We retrospectively analyzed 81 patients with end-stage ankle OA and 82 asymptomatic controls using weightbearing CT. OA patients were stratified by coronal alignment (varus n = 34, valgus n = 32, neutral n = 15) based on talar tilt measurements. Manual WBCT measurements included Tip to Subtalar Distance (TTST), Tip to Tibiotalar Distance (TTTT), syndesmosis width, talocrural angle, and TTST/TTTT ratio. Group comparisons were performed using t tests and Mann-Whitney U tests, and intra- and interrater reliability was assessed via intraclass correlation coefficient (ICC).

Results: Between OA subgroups, tip-to-tibiotalar distance (TTTT) was significantly greater in varus (26.38 mm) versus valgus ankles (20.43 mm; P = .010), suggesting relative fibular lengthening in varus deformity. TTST also differed between these subgroups (1.85 mm vs -2.51 mm; P = .020). Syndesmosis width tended to be greater in valgus ankles (6.00 mm) than in varus (4.71 mm) or normal controls (4.64 mm; P = .086). Talocrural angle was increased in valgus ankles (9.83 degrees) compared with normal (7.79 degrees) and varus (7.24 degrees; P = .090). TTTT showed the highest reliability across raters (ICC > 0.90).

Conclusion: This exploratory study identified trends suggesting fibular shortening and syndesmotic widening in valgus OA ankles, with opposite patterns in varus ankles. Although most comparisons with controls were not statistically significant, these hypothesis-generating findings suggest WBCT may detect subtle structural variations that warrant investigation in larger prospective studies.