Context: Hip- and knee-joint kinematics during drop landings are relevant to lower-extremity injury mechanisms. In clinical research the "gold standard" for joint kinematic assessment is 3-dimensional (3D) motion analysis. However, 2-dimensional (2D) kinematic analysis is an objective and feasible alternative.
Objective: To quantify the relationship between 2D and 3D hip and knee kinematics in single-leg drop landings and test for a set of 3D hip and knee kinematics that best predicts 2D kinematic measures during single-leg drop landings Design: Descriptive, comparative laboratory study.
Participants: 31 healthy college-age women (65.5 kg [SD 12.3], 168.1 cm [SD 6.7]).
Methods: Participants performed five 40-cm single-leg landings during motion capture at 240 Hz. Multiple regressions were used to predict relationships for knee and hip between 2D frontal-plane projection angles (FPPA) and 3D measurements.
Results: 2D knee FPPA had a strong relationship with 3D frontal-plane knee kinematics at initial contact (IC) (r2 = .72), which was only minimally improved with the addition of knee sagittal-plane and hip transverse-plane positions at IC (r2 = .77). In contrast, 2D knee FPPA had a low relationship with 3D knee-abduction excursion (r2 = .06). The addition of knee sagittal-plane and hip transverse-plane motions did not improve this relationship (r2 = .14). 2D hip FPPA had a moderate relationship with 3D frontal-plane hip position at IC (r2 = .52), which was strengthened with the addition of hip sagittal-plane position (r2 = .60). In addition, hip 2D FPPA into adduction excursion had a strong association with 3D hip-adduction excursion (r2 = .70).
Conclusion: 2D kinematics can predict 3D frontal-plane hip and knee position at IC during a single-leg landing but predict 3D frontal-plane knee excursion with far less accuracy.