Lower extremity kinetics during stair ambulation in patients with and without patellofemoral pain.

OBJECTIVE: To compare lower extremity kinetics during stair ascent and descent in subjects with and without patellofemoral pain.
DESIGN: A cross-sectional study utilizing a control group.
BACKGROUND: The patellofemoral joint reaction force (the resultant force between the quadriceps muscle force and patellar ligament force) increases with quadriceps force and knee flexion angle. Consequently, patients with patellofemoral pain may employ compensatory strategies to minimize pain and reduce patellofemoral joint reaction forces during activity.
METHODS: 10 individuals with a diagnosis of patellofemoral pain and 10 individuals without pain participated. Subject groups were matched on sex, age, height, and body mass. Anthropometric data, three dimensional kinematics, and ground reaction forces were used to calculate lower extremity sagittal plane moments (inverse dynamics) while subjects ascended and descended stairs at a self-selected pace. Differences in kinetic variables between groups were assessed using 2x2 (group x stair condition) analysis of variance.
RESULTS: Subjects with patellofemoral pain had decreased peak knee extensor moments during stair ascent and descent. There were no group differences in peak hip, ankle, or support moments, however, subjects with patellofemoral pain had decreased cadence (descent) compared to controls.
CONCLUSION: Subjects with patellofemoral pain had reduced peak knee extensor moments, suggesting that quadriceps avoidance was employed to reduce patellofemoral joint reaction forces. The lack of group differences in peak moments at the hip and ankle suggests that secondary compensation did not occur exclusively at the hip or ankle in this group of subjects with patellofemoral pain. RELEVANCE STATEMENT: Because stair ambulation is often used to evaluate the reproducibility of symptoms and to identify abnormal movement patterns indicative of patellofemoral pain, knowledge of lower extremity mechanics during stair negotiation is necessary to better characterize compensatory behavior in this population.