Evaluation of First Metatarsal Pronation and the Sesamoid Complex in Hallux Valgus: A Retrospective Exploratory Descriptive Radiographic Study Using a Modified Metatarso-Sesamoid View

Background: Hallux valgus (HV) is a three-dimensional deformity, and preoperative assessment of sesamoid position and first metatarsal rotation is important for surgical planning. Weight-bearing computed tomography (WBCT) enables three-dimensional assessment but was unavailable at our institution during the study period. Therefore, this study was a retrospective, exploratory, descriptive radiographic study of a modified weight-bearing metatarso-sesamoid (MS) projection, rather than a diagnostic-accuracy, comparative, or feasibility study. Methods: Between 2022 and 2024, 18 patients (16 female, 2 male; mean age 46 years, range 25–75 years) with 22 feet scheduled for HV surgery were included. Preoperative weight-bearing AP, lateral, and modified MS radiographs were evaluated. The alpha angle, sesamoid rotation angle (SRA), AOFAS tibial sesamoid grade, and the pronation/subluxation (P/S) pattern were recorded on the modified MS view. Because the alpha angle and P/S classification were originally defined on axial CT, we applied them to plain radiography as an exploratory approach. We did not validate them against a CT reference standard. Intraobserver and interobserver measurement agreement on the same existing radiographs was assessed through repeated blinded measurements by the primary observer after four weeks and through independent evaluations by a second blinded observer. We quantified reliability using ICC(2,1), unweighted kappa, and linearly weighted kappa, with 95% CIs. Technical acquisition performance was recorded. Results: On AP radiographs, IMA1–2 showed 2 mild, 15 moderate, and 5 severe deformities; HVA showed 1 normal, 11 mild, and 10 moderate cases; and Agrawal lateral sesamoid (LS) severity showed 1 mild, 20 moderate, and 1 severe case. On the modified MS view, the alpha angle ranged from 6° to 30° (mean ± SD 15.6 ± 6.6°), and the SRA from 6° to 45° (18.2 ± 8.3°). Using the CT-derived thresholds as descriptive reference labels only, alpha values were at or below 15.8° in 13 feet and above 15.8° in 9 feet, and SRA values were within the 7–18° reference range in 11 feet. AOFAS tibial sesamoid grade was 0 in 6 feet, 1 in 11, and 2 in 5. P/S patterns were P−/S− in 9 feet, P−/S+ in 4, P+/S− in 4, and P+/S+ in 5. Intraobserver ICCs were 0.996 (95% CI 0.991–0.998) for the alpha angle and 0.998 (0.994–0.999) for the SRA; interobserver ICCs were 0.988 (0.972–0.994) and 0.975 (0.947–0.981), respectively. Interobserver agreement was substantial for the P/S pattern (κ = 0.746, 95% CI 0.476–0.937) and excellent for the AOFAS grade (linear weighted κ = 0.878, 95% CI 0.663–1.000); intraobserver agreement was κ = 1.000 for both. The modified MS view provided a diagnostic image on the first acquisition in 15 of 18 patients; 3 patients required a single repeat acquisition, which was adequate in every case, and no procedure-related discomfort or intolerance was recorded. Acquisition time and radiation exposure were not recorded. Conclusions: Weight-bearing CT remains the reference standard for three-dimensional assessment. In this small cohort study, the modified MS projection could be obtained in every patient and showed high intraobserver and interobserver measurement agreement when the same existing radiographs were assessed. These findings describe measurement agreement on the same existing radiographs and the acquisition experience. Because no WBCT reference standard was available, the study cannot determine which projection reflects the underlying anatomy and provides no evidence of diagnostic accuracy, superiority over AP radiography, or clinical benefit. Standardized prospective studies with direct WBCT validation are required.