Influence of Hallux Valgus Varus Deformity on First Metatarsal Sagittal Inclination Assessment: A Comparison Between Weightbearing Radiography and Weightbearing Computed Tomography

Background: Radiographic assessment of the sagittal inclination of the first metatarsal (1M) is essential for evaluating foot disorders. However, 1M varus deviation may influence these measurements. This study aimed to determine whether hallux valgus (HV) varus deformity influences the sagittal radiographic inclination of the 1M by comparing weightbearing radiography (WBR) and weightbearing computed tomography (WBCT) images. Methods: Eighty-four feet were analyzed, including HV cases with intermetatarsal angle (IMA) >15° and control feet without HV. The sagittal inclination of the 1M, its base height, and ground lines form a rectangular scalene triangle, in which perspective changes can modify the lengths and angles of its sides. The first metatarsal declination angle (FMDA) and length of the first metatarsal (L1M) were used to assess the influence of 1M varus on sagittal alignment differences between WBR and WBCT. Results: < .05). Agreement analysis demonstrated strong concordance between WBR and WBCT measurements, indicating comparable values with minimal systematic bias. Conclusion: In patients with IMA >15°, forefoot geometric changes were reflected with modest L1M differences, although their clinical impact should be interpreted cautiously. Importantly, these changes did not affect FMDA, which remained stable across imaging modalities. The strong agreement between WBR and WBCT supports FMDA as a reliable parameter for assessing 1M sagittal alignment and planning realignment procedures, irrespective of HV severity. Level of Evidence: Level IV, cross-sectional study.