Introduction: The aim of this study was to determine if using a direct kinematic (DK) or inverse kinematic (IK) modelling approach could influence the estimation of knee joint kinematics, kinetics and ACL injury risk classification during unanticipated side-cutting.
Methods: Three-dimensional motion and force data of 34 amateur Australian rules footballers conducting unanticipated side-cutting manoeuvres were collected. The model used during the DK modelling approach was an eight segment lower body model with the hip, knee and ankle free to move in six degrees-of-freedom. During the IK modelling approach the same eight segment model was used, however translational constraints were imposed on the hip, knee and ankle joints. The similarity between kinematic and kinetic waveforms was evaluated using the root mean square difference (RMSD) and one-dimensional statistical parametric mapping (SPM1D). Classification of an athlete's ACL injury risk was determined by correlating their peak knee moments with a pre-defined injury risk threshold.
Results: The greatest RMSD occurred in the frontal plane joint angles (RMSD: 10.86[degrees]) and moments (RMSD: 0.67+/-0.18 N[middle dot]m[middle dot]kg-1), which were also shown to be significantly different throughout the stance phase in the SPM1D analysis. Both DK and IK modelling approaches classified the same athletes as being 'at risk' of ACL injury.
Conclusions: The choice of a DK or IK modelling approach affected frontal plane estimates of knee joint angles and peak knee moments during the weight acceptance phase of unanticipated side-cutting. However, both modelling approaches were similar in their classification of an athlete's ACL injury risk.
(C) 2014 American College of Sports Medicine