A Prospective Investigation of Biomechanical Risk Factors for Anterior Knee Pain

Anterior knee pain is one of the most common chronic knee conditions in the United States; however, little research has been done to determine the risk factors for this injury. The main objective of this investigation was to determine the biomechanical risk factors for anterior knee pain in a military population. We assessed lower extremity kinematics, kinetics, muscle strength, and postural measures as risk factors for the development of anterior knee pain. A total of 1597 participants were enrolled in this investigation. Each participant underwent baseline data collection during their first summer of enrollment at the United States Naval Academy. Baseline data collection included three-dimensional motion analysis during a jump-landing task, six lower extremity isometric strength tests, and measurement of navicular drop and Q-angle. Following baseline data collection participants were followed from their date of enrollment to January 15, 2008. Due to the enrollment of participants over the summers of 2005, 2006, and 2007, the follow up time for participants varied. Forty (females=24, males=16) of the enrolled participants were diagnosed with anterior knee pain over the course of the follow up period. Due to incomplete data collection for some of the participants, the cohort of non-injured subjects reduced to 1279. Poisson regression analyses were performed to determine the risk factors for the development of anterior knee pain. We also performed a 2x2 (gender x group) ANOVA to determine if there was a difference between genders for the risk factors for anterior knee pain. Poisson and logistic regression analyses were performed to determine if gender significantly predicted the incidence rate or prevalence of anterior knee pain. Risk factors for the development of anterior knee pain included decreased knee flexion angle and vertical ground reaction force and increased hip internal rotation angle during the jump-landing task. Additionally, decreased knee flexion and extension strength, increased hip external rotation strength, and increased navicular drop were risk factors for the development of anterior knee pain. There were no significant differences between males and females who developed anterior knee pain for the risk factor variables. The incidence rate of anterior knee pain in females was significantly greater than males, with females having 2.23 times (95% CI: 1.19, 4.20) the rate of anterior knee pain compared to males. There was no difference in the prevalence of anterior knee pain between males and females. Decreased strength, increased hip internal rotation angle, and increased navicular drop may be predisposing individuals to the development of anterior knee pain due to these muscle imbalances and malalignments leading to patellar malalignment. This suggests that prevention programs should focus on increasing strength of the lower extremity musculature along with instructing proper mechanics during dynamic movements in order to decrease the incidence of anterior knee pain. Additionally, targeting prevention programs towards females may help to decrease the incidence rate of anterior knee pain