BACKGROUND:Hallux abducto valgus (HAV) is a triplane deformity with recent attention given to the significance of correcting the coronal plane component. This study explored the accuracy of the forefoot axial study as a standard radiographic assessment method compared to weight-bearing CT scanning.METHODS:Twelve feet with HAV from 12 subjects were included in this study. Three images of the affected foot were taken: 1) forefoot axial radiograph (FFA), 2) weight-bearing CT scan with the foot in a position of a) maximum pronation (Pronated CT) and b) maximum supination (Supinated CT). Five investigators (three faculty members and two podiatric16 medical students) determined the sesamoid rotation angle (SRA) from each of the images. The measurements from a single investigator were used to compare the SRA means from each of the image types, while those from all five investigators were used to determine reliability.RESULTS:The mean SRA for the pronated CT position was 22.1 {plus minus} 7.6 degrees, while that for the supinated CT image was 10.5 {plus minus} 5.0 degrees. In comparison, the mean SRA determined from the FFA image was 12.2 {plus minus} 9.4 degrees. The mean SRA from the Pronated CT was significantly greater than both the Supinated CT (p<0.001) and the FFA SRA (p<0.005). There were no significant differences in mean SRA between the FFA and Supinated CT images (p=1.000). Results indicated a high reliability in measurements between investigators.CONCLUSIONS:Using weight-bearing CT, the findings of this study indicate that the sesamoids significantly alter their position in the coronal plane, as determined by the SRA, with changes in weight-bearing subtalar joint position. Moreover, the affected foot positioning required for determining the SRA from the forefoot axial radiograph appears to significantly underestimate the true SRA value. Thus, the use of this image in surgical HAV planning is called into question.

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