There are potential limitations with using a 2D analysis of limb motion; McLean et al. [19] though reported that 2-D video analysis was suitable to screen individuals with excessive knee valgus. Both McLean et al. [19] and Willson and Davis [4] stated that this conclusion should be viewed with caution as the 2D method lacks sensitivity to measure small changes in angles. This study has shown significantly larger differences between symptomatic and asymptomatic knees than the previously reported standard error of measurement [14] demonstrating the differences to be real and beyond measurement error. McLean et al. [19] found an average peak 2-D knee valgus angle accounted for 58% to 64% of the variance in average peak 3-D knee valgus angle between subjects during side-step and side-jump activities, demonstrating a degree of validity to the measure. Willson and Davis [4] found 2-D knee valgus reflected 23% to 30% of the variance of 3-D measurements during single leg squat, but interestingly found knee valgus to be significantly correlated with knee external rotation (r = 0.54, p = 0.001) and hip adduction (r = 0.32, p = 0.04), which are major components of the “medial collapse” 2-D knee valgus angle which it aims to represent.
This study is cross sectional in nature and so its nature prevents making direct causal links between the altered kinematics seen in the patient group and pain. It cannot be concluded that the knee valgus position caused the pain or the pain created the altered mechanics. What is significant is that without the correction of these mechanical issues, the pain is likely to continue and potentially worsen, because of the altered stresses placed on the PFJ.