| Background: Patellofemoral pain syndrome (PFPS) also known as anterior knee pain is a common knee injury among runners. During running, people with PFPS demonstrate abnormal mechanics such as increased hip adduction and hip internal rotation (Dierks, Manal, Hamill, & Davis, 2008; Souza & Powers, 2009; Willson & Davis, 2008). Similar abnormal mechanics are also exhibited when people with PFPS perform a single limb squat (Crossley et al., 2011; Levinger et al., 2007; Nakagawa et al., 2012; Souza & Powers, 2009; Willson et al., 2008). The single limb squat (SLS) is a clinical assessment to examine the kinematics occurring during running. The mechanics during the two activities (SLS and running) are assumed to be related. However, the two tasks have never been directly compared in the same subjects. Hence, the current study examines the relationship between the hip and knee mechanics occurring during SLS and running. All previous studies identifying abnormal running kinematics have been cross-sectional in nature and only examined the kinematics after an injury such as PFPS has occurred (Bolgla et al., 2008; Crossley et al., 2011; Souza & Powers, 2009; Willson et al., 2008; Willson & Davis, 2008b). The current study examines running and SLS kinematics prior to an occurrence of anterior knee pain in subjects training to run a marathon. The aims of the current study are: 1) to determine if three-dimensional lower extremity kinematics during a SLS are associated with lower extremity kinematics during treadmill running, 2) to determine if three-dimensional lower extremity kinetic parameters of the single limb squat strengthen the relationship between medial-lateral and axial lower extremity running kinematics, and 3) to determine if either running or single limb squat kinematics, or single limb squat kinetics will be associated with development of self-reported anterior knee pain during the course of a marathon training program? Methods: Forty four subjects were investigated prior to and during their training for a marathon. Prior to marathon training, an eight camera VICON motion capture system was used to obtain single limb squat and running kinematics. A Bertec force plate measured ground reactions forces while subjects performed a single limb squat. During marathon training, anterior knee pain questionnaires were administered at three different times to all subjects. Questions asked in the questionnaires included any experience of knee pain in the last 7 days, the location of the knee pain experienced, and the Kujala questionnaire. To focus on variables that best identify subjects with anterior knee pain, answers to only the questions in the Kujala questionnaire considered most related to PFPS were considered: 1 (limp), 4 (climbing stairs), 6 (running), 8 (prolonged sitting with knees flexed), 9 (pain) and 11 (abnormal painful patellar movement) (Kujala et al., 1993). Anterior knee pain was classified as subjects responding yes to all three questions: 1) having any knee pain in the last 7 days and 2) having anterior knee pain at least once and, 3) answering any of the non-pain free options to any of the subset of Kujala questions at least once. Results: There was no significant association between SLS knee abduction excursion and running knee abduction excursion. There was no significant association between SLS hip internal rotation excursion. However, univariate linear regression found significant association between peak knee abduction angle during a SLS and during running (Multiple R-squared = 0.62, Model p-value <0.05). Univariate linear regression found significant association between peak hip internal rotation during a SLS and running (Multiple R-squared = 0.52, Model p-value<0.05). Multivariate regression found a negative significant association between net hip abductor muscle moment during SLS and knee abduction excursion during running (Estimate = -7.46, p-value <0.05). Logistic regression did not find a significant relationship between running and SLS kinematic excursions and the incidence of anterior knee pain during marathon training. While examining peak kinematic variables, backward stepwise logistic regression found a significant relationship between female gender and peak hip internal rotation angle during running to incidence of anterior knee pain during marathon training. Females were 9 times more likely to experience anterior knee pain compared to males. Subjects with lesser peak hip internal rotation during running were 1.15 times more likely to experience anterior knee pain. Univariate t-tests found a significant association between higher peak knee abduction angle during SLS and anterior knee pain (p-value = 0.02). Similarly, there was a significant relationship between higher peak knee abduction angle during running and anterior knee pain (p-value = 0.04). Conclusion: There were no significant associations between SLS excursions and running excursions. These findings could be due to difference in the definition of excursion across SLS and running. Significant and strong associations between SLS and running peak kinematics imply that peak kinematics and kinetics during a SLS are representative of those during running. Thereby, the results support the use of a SLS as a clinical tool to understand the mechanics during running. These findings and related theory support that the female gender and increased peak knee abduction angles are risk factors for anterior knee pain during marathon training. |
