Effect of gait pattern on patellofemoral joint stress during walking in individuals with patellar instability

Background: Patellar instability is a common injury among young, active individuals resulting in increased risk for future patellofemoral osteoarthritis. The purpose of this study is to quantify the effect of gait pattern on patellofemoral joint stress in those with patellar instability. Methods: Individuals with patellar instability (n = 17) completed an instrumented gait analysis. A mathematical model, with sagittal plane knee angle and knee moment as inputs, was used to estimate patellofemoral joint stress during stance. Individuals were grouped by presenting with an extension dominant knee moment or a flexion dominant knee moment. Patellofemoral joint stress and knee and hip mechanics were compared between affected limbs. The injured limb of the extension dominant group was also compared to matched healthy control participants. Findings: Extension dominant and flexion dominant groups had similar patellofemoral joint stress magnitudes (p = 0.37) throughout stance phase, but the flexion dominant group reached peak stress at a significantly later percentage of stance (p < 0.05) and at a smaller knee flexion angle (p < 0.05). There were no significant differences in peak or timing of patellofemoral joint stress or knee angle at peak stress between the extension dominant group and a matched set of healthy controls, but differences in other knee and hip mechanics were present. Interpretation: The flexion dominant group's peak patellofemoral joint stress occurred later in stance placing it above the trochlear groove, perhaps loading cartilage unaccustomed to high magnitudes, and may contribute to the development of patellofemoral osteoarthritis through impaired adaptation to altered loading.