Quantitative and qualitative assessment of frontal plane knee motion in males and females: A reliability and validity study.

BACKGROUND: The aim was to determine reliability and validity of frontal plane projection angle (FPPA) and visual assessments (VA) in both males and females. METHODS: Fifty-four participants (30 females) performed lateral step-downs while kinematics were recorded by two-dimensional and three-dimensional analyses. Two raters viewed the videos, extracted images, and measured the FPPA (quantitative). Using the videos, the raters also categorized (qualitative VA) each participant's motion as demonstrating dynamic valgus (>10° valgus), dynamic varus (>10° varus), or no change. Reliability was assessed for FPPA and VA using intraclass correlation coefficients and Kappa, respectively. Validity was determined by comparing the FPPA to three-dimensional measures (Pearson correlations) and comparing the VA to both FPPA and standard reference 3D kinematics (Kappa). RESULTS: FPPA showed good-excellent reliability (ICC = 0.850-0.998). VA showed minimal-moderate reliability (κ = 0.370-0.766). The FPPA showed large correlations (r = -0.514-0.531) with hip adduction in both sexes but only a moderate relationship with knee abduction in males (r = 0.427-0.445). VA showed no-weak (κ = 0.153-0.475) and weak-moderate (κ = 0.455-0.698) agreement compared to FPPA and no-weak (κ = -0.300-0.183) and no-minimal (κ = -0.078-0.027) disagreement compared to the reference standard 3D kinematics in males and females, respectively. CONCLUSION: The quantitative FPPA is more reliable and valid than qualitative VA of frontal knee plane motion.