Navicular Height by Weight-bearing Ultrasound: A Reliable and Valid Tool for Assessing the Medial Longitudinal Arch in Physically Active Adults

Background: The medial longitudinal arch (MLA) height is an important clinical indicator of foot posture, linked to injury risk and rehabilitation targets. Assessment of navicular height (NH) in standing position is commonly used as a marker of MLA height. Methods such as palpation and imaging face limitations with operator variability, accessibility, and radiation exposure. Ultrasonography may be a practical alternative, but its reliability compared to established methods needs further evaluation. The research objective was to assess the reliability and validity of plantar ultrasonographic navicular height measures (US-NH) in standing position using a novel ultrasonography platform. Methods: A test-retest study design was adopted across 2 cohorts: cohort study 1 (CS1, 2023; n = 16) and cohort study 2 (CS2, 2024; n = 30), using the standing ultrasonography platform. Intra- and inter-rater intraclass correlation coefficients (ICCs) were assessed to evaluate method reliability. Validity was assessed using cadaveric dissection as a gold standard. Results: US-NH demonstrated excellent intra-rater reliability (ICC 0.956, 95% CI: 0.934-0.971), improving from good reliability in CS1 (ICC 0.827, 95% CI: 0.675-0.912) to excellent in CS2 (ICC 0.981, 95% CI: 0.969-0.989) after methodologic refinements. Inter-rater reliability also increased markedly, from poor in CS1 (ICC 0.459, 95% CI: 0.240-0.819) to excellent in CS2 (ICC 0.964, 95% CI: 0.940-0.978), indicating reduced operator-dependent variability. Dissection confirmed the bone visualised with weight-bearing ultrasonography corresponded accurately to the plantar navicular surface. Conclusion: Ultrasonography is a reliable, valid, and radiation-free method for measuring navicular height, in a physically active population. Dissections demonstrated the high validity of ultrasonographic assessment when compared to direct anatomical measurement. Level of Evidence: Level V, mechanism-based reasoning.