Reliability and Agreement of a Dual-Method RadiographicStandard vs. Clinical Goniometry for Shank–ForefootAlignment A GRRAS-Compliant Study

Abstract

Introduction: Forefoot varus prevalence varies widely (8.6–83.67%) and may be attributableto the lack of a gold standard. Clinical methods are limited by subjective positioning andlandmark variability. This study established a reliable radiographic reference using a dualmethodapproach. Methods: Following GRRAS guidelines, 70 lower limbs (35 participants)were evaluated using consecutive sampling. Three blinded investigators performed themeasurements. Reliability was assessed throughout inter-rater (30-min interval) and intrarater(≥30-day washout) sessions. Dual radiographic methods (metallic nail vs. radiopaquemarkers) were compared against standardized goniometry. The analysis included ICC(2,1)and ICC(3,1), SEM, MDC95, and Bland–Altman plots, with a significance threshold ofp < 0.005. A sensitivity analysis using one randomly selected limb per participant (n = 35)confirmed the robustness of the findings. Results: Participants (mean age 32.77 ± 10.8 years,54% female) had a mean forefoot varus of 15.53 ± 7.35◦, with a prevalence of 97.1% (≥0◦).Goniometric inter-rater reliability was excellent (ICC = 0.987, MDC95 = 1.382◦). The markerbasedradiographic method demonstrated excellent intra-rater reliability (ICC = 0.906,MDC95 = 1.129◦). The agreement between goniometry and marker-based radiographywas strong (ICC = 0.898). All analyses surpassed the p < 0.005 threshold. No significantdifferences were found for sex or laterality (p > 0.005). Conclusions: Marker-based radiographyprovides a validated reference standard with excellent reliability. Standardizedclinical goniometry demonstrated excellent reliability and strong radiographic agreement,making it appropriate for routine assessment (changes > 1.4◦ represent true structuralchange). Radiography should be reserved for research or definitive structural confirmation.Limitations include the lack of inter-reader radiographic reproducibility assessment andlimited generalizability to young adults (mean age 33 years) with predominantly forefootvarus alignment.