Healthy 3D knee kinematics during gait: Differences between women and men, and correlation with x-ray alignment

Background: Normal 3D knee kinematics during gait is still not well understood, especially regarding differences between women and men. Research question: The objective of the present study was to characterize 3D knee kinematics during gait in healthy women and men with a validated tool. Methods: Knee kinematics was analysed with the KneeKG (TM) system in 90 healthy subjects (49 females and 41 males). 3D knee rotations were compared between women and men, and between right and left knees. Each subject underwent full-length weight-bearing x-rays. Correlations between abduction-adduction angles and lower-limb alignment measures on x-rays were assessed. Results: In the frontal plane, 2.0-5.0 degrees more abduction occurred in women compared to men (0.000 <= p <= 0.015) throughout the entire gait cycle. In the transverse plane, 2.4-3.7 degrees more external tibial rotation was seen in women than in men (0.002 <= p <= 0.041) during the initial and mid-swing phases. No difference was found between the right and left knees. Low correlations ( -0.52 <= r <= -0.41, p < 0.001) were observed between radiographic hip-knee-ankle angle (HKA) and abduction-adduction angles throughout the stance phase. Significance: Kinematic differences between women and men in the frontal plane can be partly explained by their anatomical differences: women were less in varus than men (HKA of -0.8 degrees vs. -2.6 degrees, p < 0.001). Our study contributes to a better understanding of healthy 3D knee kinematics during gait and highlights the need for accounting of gender differences in future investigations. Better knowledge of natural knee kinematics will be helpful in assessing pathological gait patterns or determining the efficiency of conservative and surgical treatments to restore normal kinematics.