Inaccuracy of Forefoot Axial Radiographs in Determining the Coronal Plane Angle of Sesamoid Rotation in Adult Hallux Valgus Deformity: A Study Using Weightbearing Computed Tomography

Abstract

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.

The Assessment of First Metatarsal Rotation in the Normal Adult Population Using Weightbearing Computed Tomography

“…While the use of WBCT is a strength of our study, a key limitation is the use of 2D measurements, which are prone to error depending on subtle changes on foot position. 13 However, we found that the measurements taken in this study were reliable and reproducible. Other limitations include the failure to correlate the findings to patient outcome scores and function, although all patients in this study were radiologically normal.…”

Assessing the Rotation of the First Metatarsal on Computed Tomography Scans: A Systematic Literature Review

“…Eleven studies used 2D measurements on a CT slice. * Matsubara et al, 26 Cruz et al, 6 and Sadamasu et al 37 49 Mahmoud et al, 25 Kawalec et al, 19 and Scheele et al 40…”

“…Both the α angle and MPA have shown excellent interobserver and intraobserver reliability in different studies. 4,19,25,26,37,40,49 The α angle has been measured in 3 studies, and 2 studies looking at its reliability included 88 patients in total. 20,25,32 The interobserver reliability (ICC) was 0.93 and intraobserver reliability (ICC) for the α angle was between 0.7 and 0.96.…”

“…However, Pearson correlations of the α angle with respect to HVA and IMA showed relatively weak positive relationships. The authors * References 4,6,12,19,20,25,26,32,37,39,48. measured the α angle on the largest number of patients, but there were no data regarding the reliability of the measurements.…”

“…Since 3 reviewers were used, the ICC for interobserver reliability was between 0.79 and 0.87, and the ICC for intraobserver reliability was 0.81. Kawalec et al 19 used WBCT to measure SRA in 15 patients with hallux valgus. They compared a forefoot axial radiograph to measurements of the SRA with the foot in a maximally pronated position and the foot in a maximally supinated position.…”