Assessing the Reliability and Minimal Detectable Change of Frontal Plane Projection Angles During Single-leg Tasks in Individuals with Patellofemoral Pain

This study conducted a secondary analysis of a previous study to evaluate the test-retest reliability, standard error of measurement (SEM), and minimal detectable change (MDC) of frontal plane projection angles across five single-leg tasks in individuals with patellofemoral pain. Two-dimensional video data were collected from ten individuals with predominantly unilateral PFP (6 males and 4 females; 28.2 ± 6.9 years; BMI = 26.8 ± 6.7 kg/m²). Participants performed single-leg squat, single-leg landing, single-leg hop, forward step-down, and lateral step-down across two testing sessions. frontal plane projection angles were measured at peak knee flexion for each task, including trunk lean angle, knee frontal plane projection angles, hip frontal plane projection angles, and dynamic valgus index. Test-retest reliability was assessed using intraclass correlation coefficients (ICCs). SEM was calculated as SD × √(1–ICC), and MDC as SEM × 1.96 × √2. Individuals with patellofemoral pain demonstrated lower reliability and higher SEM and MDC values for hip frontal plane projection angles during single-leg squat and lateral step down, knee frontal plane projection angles during single-leg landing, and trunk lean angle during single-leg squat compared to previously reported values in pain free populations.