Lower extremity mechanics of females with and without patellofemoral pain across activities with progressively greater task demands

BACKGROUND: Patellofemoral pain is commonly associated with lower extremity joint rotations that decrease retropatellar contact area and subsequently increase retropatellar stress during weightbearing activities. People with patellofemoral pain are thought to be capable of avoiding such harmful mechanics during activities with low external demands. However, this may not be possible during more demanding activities. The purpose of this study was to analyze lower extremity mechanics in females with and without patellofemoral pain during three different activities. Specifically, we sought to determine if differences between groups increase with increasingly demanding activities. METHODS: 20 females with patellofemoral pain and 20 healthy female controls performed single leg squats, running, and repetitive single leg jumps as their three-dimensional lower extremity mechanics were recorded. Transverse and frontal plane hip and knee kinematics were compared between groups for all activities. FINDINGS: Differences in the variables of interest between groups did not generally depend on the nature of the activity. The patellofemoral pain group performed all three activities with 4.3 degrees greater knee external rotation (P=0.06), 3.5 degrees greater hip adduction (P=0.012), and 3.9 degrees decreased hip internal rotation with respect to the control group (P=0.01). INTERPRETATION: These results suggest that females with patellofemoral pain do not employ different mechanics as demand of the activity increases. Rather, females with patellofemoral pain seem to demonstrate similar abnormal lower extremity mechanics across a variety of activities.