Association between ultrasound and radiographic measurements of the medial longitudinal arch: a cross-sectional study

Abstract Background The objective of this study was to compare measurements of the medial cuneiform height (MCH) and navicular height (NH)—indicators of the medial longitudinal arch (MLA)—obtained using an ultrasound imaging system (US) with values measured by X-ray (XR method), to clarify the relationship between the two measurement methods and to identify the characteristics of the US-based measurement method. Methods The study included 30 healthy adults (22 men, 8 women). MCH and NH, which are indicators of the medial longitudinal arch (MLA), were measured using ultrasound (the US-SG method, in which the lower end of the probe is placed along the floor) and using the X-ray method. Measurements were taken in both seated and simulated single-leg stance conditions. The relationship between the two measurement methods for MCH and NH was examined using correlation analysis, and systematic differences between the methods were characterized using Bland–Altman analysis. Additionally, to assess the reliability of the US-SG method, inter-observer reliability was evaluated in a separate group of 10 participants. Results For MCH measured using the US-SG method, the correlation with the XR method was low ( r = 0.501) or no significant correlation was observed ( p > 0.05). In contrast, for NH, the correlation ranged from r = 0.684 to 0.710. Bland-Altman analysis revealed proportional error only in the simulated single-leg stance condition for NH. Inter-examiner reliability ranged from 0.848 to 0.966. Conclusion The MLA values obtained using the US-SG method were associated with those obtained using the XR method. However, since systematic errors were observed between the two measurement methods, further investigation is necessary for the clinical application of the US-SG method.