Is markerless, smart phone recorded two-dimensional video a clinically useful measure of relevant lower limb kinematics in runners with patellofemoral pain? A validity and reliability study.

Objective: Investigate the validity and reliability of markerless, smart phone collected, two-dimensional (2D) video, analysed using the 'Hudl technique' application, compared to three-dimensional (3D) kinematics during running, in participants with patellofemoral pain (PFP).

Methods: Validity/reliability study. Methods: Biomechanics laboratory. Methods: Males/females with PFP (n = 21, 10 males, 11 females, age 32.1 months [±12.9]). Methods: Manually synchronised 2D and 3D measurement of peak hip adduction (HADD) and peak knee flexion (KFLEX) during running.

Results: 2D and 3D measures of peak KFLEX (p = 0.02, d = 1.13), but not peak HADD (p = 0.25, d = -0.27), differed significantly. Poor validity was identified for 2D measurement of peak HADD (ICC 0.06, 95% CI -0.35, 0.47) and peak KFLEX ICC 0.42, 95% CI (-0.10, 0.75). Moderate intra-rater reliability was identified for both variables (ICC 0.61-65), alongside moderate inter-rater reliability for peak KFLEX (ICC 0.71) and poor inter-rater reliability for peak HADD (ICC 0.31).

Conclusions: Measurement of peak HADD and KFLEX in runners with PFP using markerless, smart phone collected 2D video, analysed using the Hudl technique Application is invalid, with poor to moderate reliability. Investigation of alternate 2D video approaches to increase precision is warranted. At present, 2D video analysis of running using Hudl Technique cannot be advocated.