Reliability and Agreement of a Dual-Method Radiographic Standard vs. Clinical Goniometry for Shank–Forefoot Alignment: A GRRAS-Compliant Study

Introduction: Forefoot varus prevalence varies widely (8.6–83.67%) and may be attributable to the lack of a gold standard. Clinical methods are limited by subjective positioning and landmark variability. This study established a reliable radiographic reference using a dual-method approach. Methods: Following GRRAS guidelines, 70 lower limbs (35 participants) were evaluated using consecutive sampling. Three blinded investigators performed the measurements. Reliability was assessed throughout inter-rater (30-min interval) and intra-rater (≥30-day washout) sessions. Dual radiographic methods (metallic nail vs. radiopaque markers) 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 of p < 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 marker-based radiographic method demonstrated excellent intra-rater reliability (ICC = 0.906, MDC95 = 1.129°). The agreement between goniometry and marker-based radiography was strong (ICC = 0.898). All analyses surpassed the p < 0.005 threshold. No significant differences were found for sex or laterality (p > 0.005). Conclusions: Marker-based radiography provides a validated reference standard with excellent reliability. Standardized clinical goniometry demonstrated excellent reliability and strong radiographic agreement, making it appropriate for routine assessment (changes > 1.4° represent true structural change). Radiography should be reserved for research or definitive structural confirmation. Limitations include the lack of inter-reader radiographic reproducibility assessment and limited generalizability to young adults (mean age 33 years) with predominantly forefoot varus alignment.