Reliability and criterion validity of hip and knee frontal plane projection angles and dynamic valgus index in those with patellofemoral pain

Title: Reliability and criterion validity of hip and knee frontal plane projection angles and dynamic valgus index in those with patellofemoral pain
Name: Erin Lally
Primary Presenters: Erin Marie Lally
College of Health Sciences
Research Doctorate (PhD)
Faculty Sponsor(s): Dr. Jennifer Earl-Boehm

Context: Poor hip and knee biomechanics have been demonstrated prospectively in those with patellofemoral pain (PFP). Using two-dimensional motion analysis (2DMA) to evaluate risky movement patterns is more accessible to clinicians compared to 3-dimensional motion analysis (3DMA). Knee frontal plane projection angle (kFPPA), hip frontal plane projection angle (hFPPA), and dynamic valgus index (DVI) are 2D measures used to assess movements that exacerbate PFP. These assessments have acceptable reliability and validity when analyzing single-leg squats in those with PFP. However, it is unknown if these 2D assessments are reliable and valid to analyze a step-down, a task frequently used to evaluate movement. Therefore, the purpose of this study was to determine intra- and inter-rater reliability and criterion validity of kFPPA, hFPPA, and DVI during the step-down in those with PFP. Methods: 39 participants (34.18 ± 7.41years, 1.70± .01m, 81.03 ± 19.36kg, duration of pain: 68.67±85.08 months, anterior knee pain scale: 80.49± 7.87, visual analog scale:2.08± 2.02) had 3D and 2D kinematic data collected simultaneously while performing the step-down. Participants were instructed to begin in a single limb stance on a 4-inch box and lower the non-stance foot to the floor without bearing weight and return to the starting position at the standardized rate of 60 bpm. Variables of interest were 3D hip and knee sagittal, frontal, and transverse joint angles at maximum knee flexion. 3D DVI was calculated as the sum of hip and knee frontal and transverse angles. Two experienced raters calculated 2D kFPPA, hFPPA, and DVI independently at two time points (12.8±7.05 days between ratings). Averages of 2D and 3D angles were calculated for data analysis. Intra-class correlations (ICC) were performed to establish intra- and inter-rater reliability. Bivariate correlations between 3D and 2D variables were used to determine criterion validity. Results: Intra- and inter-rater reliability of each 2D measure was excellent. 2D kFPPA was moderately correlated to 3D knee transverse angles. hFPPA was moderately correlated to 3D hip frontal angles, 3D hip transverse angles, and largely correlated to 3D DVI. 2D DVI was moderately correlated to hip transverse angles (Table 1). Conclusion: To evaluate movement during a step-down task 2D kFPPA, hFPPA, and DVI have excellent reliability within and between clinicians. hFPPA demonstrated the greatest criterion validity against 3D DVI, meaning it is a potential alternative to measures of 3D hip and knee frontal and transverse motion during the step-down in those with PFP. Due to the criterion validity findings of this study, kFPPA and 2D DVI cannot be recommended for clinical use to analyze the step-down over hFPPA. Our findings also support that reliability and validity of 2D movement assessments are task dependent, as 2D DVI was found to be most appropriate to analyze single-leg squats. Word count: 449 (out of 450)