Results

1. Patterns of Hip Flexion Motion Predict Knee Abduction Torques during a Single-leg Land and Cut Maneuver KristofKipp, Scott G McLean, Riann M Palmieri-Smith University of Michigan, Ann Arbor, MI, USA Results Introduction Methods An eigenvector decomposition method was used to extract principal components from each data input matrix. Principal components were normalized to unit vectors, in order to account for magnitude differences between principal components, and projected onto the respective waveforms from which the principal components were originally extracted. The summation of these projections across the stance phase gave a set of PC scores that expressed the extent to which each principal component contributed to the original waveforms for each participant. The PC scores for each of the retained principal components were then subjected to statistical analysis. A forward step-wise regression model, with PC scores as dependent variables, was used to establish a prediction equation for peak ensemble-averaged knee abduction torque. Normality and residual plots were checked to ensure that assumptions of the test statistic were met. Conditions for entry and removal into the regression model were set at 0.05 and 0.10, respectively. Impulsive frontal plane knee joint torques directly strain the anterior cruciate ligament (ACL) and therefore may contribute to ACL injury risk. The ability to identify the most pertinent kinematic movement patterns that are associated with deleterious knee joint torques may assist in the development of screening protocols and aid in the refinement of current injury prevention strategies. Principal component analysis (PCA) provides a means to extract characteristic features of motion patterns across entire movements. PCA may prove particularly suitable to establish relationships between kinematic movement characteristics and peak knee joint torques. The second principal component extracted from the hip joint flexion rotation (PC2HipFlexion) that entered into the regression model captured the magnitude of hip flexion motion during the first half of the stance phase (Figure 2). Objective Figure 2 Hip flexion angles (degrees) across the stance phase of the single-leg land and cut maneuver for subjects with high (white line) and low (black line) PC2HipFlexion scores. To establish a prediction model for frontal plane knee joint torques based on motion patterns derived from PCA.  Results The results from the regression analysis indicated that only one principal component (PC2HipFlexion) was a significant predictor of knee abduction torque (Figure 1). Methods Conclusion Eighteen healthy female NCAA Division 1 athletes (mean ±SD age: 19.7±1.7 yrs; height: 1.67±0.06 m; mass: 61.5±6.0 kg) were recruited to participate in this study. Written informed consent was obtained from all participants. Biomechanical data were collected during the execution of a single-leg land-and-cut maneuver that required participants to initiate a forward two-legged jump, land on the dominant leg, and execute a side cut away from the landing leg. Joint angles of the hip, knee, and ankle were computed in three dimensions. The resultant external joint torque acting at the knee in the frontal plane was calculated and normalized to participant mass and height. Kinematic and kinetic time-series data were time-normalized to 100% of stance phase and ensemble-averaged. These mean-removed, ensemble averages were combined into 8 data matrices. These data matrices were used as input to the PCA. Greater hip flexion motion during the first half of the stance phase of a single-leg land-and-cut maneuver is associated with greater external knee joint torques in the frontal plane. Injury screening and prevention protocols should consider hip flexion motion upon single-leg landing as a modifiable characteristic that could decrease the magnitude of frontal plane knee joint torques and potentially decrease the likelihood of ACL injury. Acknowledgements This research was funded in part through the National Football League Charities. The authors would also like to acknowledge assistance from the National Institutes of Health (NIH) Grant # NIH Grant T32 HD007422-19. Figure 1: Knee abduction torques (N∙m/kg∙m) across the stance phase of the single-leg land and cut maneuver for subjects with high (white line) and low (yellow line) PC2HipFlexion scores.