The reliability and validity of a visual analog scale for rating the single leg squat test

Background The single leg squat test (SLST) is commonly used for visual movement assessment in subjects with lower extremity injuries. While current methods utilize ordinal rating categorization, adopting a visual analog scale (VAS) may offer potential advantages. The study aims to determine the intra-rater, inter-rater reliability, and validity of a visual analog scale (VAS) for rating the single leg squat test (SLST) in subjects with lower extremity injuries. Methods 58 subjects with lower extremity injuries participated. Intra-rater reliability was assessed by a physical therapist at 1-week and 2-week intervals. Single session inter-rater reliability was assessed by two physical therapists. A 10 cm VAS was used to measure trunk lateral flexion, hip adduction, and dynamic knee valgus during the SLST. Intra-class correlation coefficients (ICC) assessed intra-rater and inter-rater reliability. Validity was assessed by comparing VAS scores to 2-D kinematic analysis. Results Intra-rater reliability was good at both 1 week (ICC = 0.81–0.92, MDC = 1.2–2.2 cm) and 2 weeks (ICC = 0.77–0.79, MDC = 2.7–3 cm). Inter-rater reliability was good to excellent (ICC = 0.78–0.93, MDD = 1–2.6 cm). The correlation between visual assessment and 2-D kinematic analysis was moderate to good ( r = 0.66–0.78). Conclusion Preliminary data indicate that VAS reliably and validly rates SLST in individuals with lower-extremity injuries, allowing calculation of minimal detectable change and minimal detectable difference to support clinical interpretation. The MDC and MDD values established for trunk lateral flexion, hip adduction, and dynamic knee valgus allows clinicians to objectively determine if scores between repeated measurement and two raters are different.