Influence of lower limb rotation on hindfoot alignment using a conventional two-dimensional radiographic technique

Abstract

Background: Rotation is one of the variables explaining lack of reproducibility in assessing hindfoot alignment. The hypothesis for this study was that a mathematical model predicts how this modifies radiographic hindfoot alignment measurements.

Methods: A cadaveric lower limb, disjointed at knee level, was used. Sagittal and coronal planes were fixed using a custom clamp. Standard AP views were shot every five degrees and measured hindfoot alignments were compared to theoretical values obtained from a mathematical simulation.

Results: Hindfoot angle was 7.04° at 0° rotation and 2.11° at -90°. Intra-class and inter-investigator correlation was 0.863. The t-test showed no significant difference (p=0.73). Intra-investigator correlation was 0.957. The R2 correlation index was 0.852.

Conclusions: The mathematical model accurately predicted the variations of the hindfoot angle which was maximum when the foot was aligned with the X-rays source. It then decreased when the foot rotated away, following a parabolic curve.

Keywords: Alignment; Foot; Forefoot; Hindfoot; Meary; Radiography.