Gender differences in knee kinematics and its possible consequences.

AIM To analyze anatomic and kinematic characteristics of male and female knees in the sagittal plane. METHODS Ten healthy male and 10 healthy female participants performed extension of their right lower leg in non-weight bearing and weight bearing conditions. The centers of knee joint motion were obtained by videographic motion analysis, and radii of condylar curves were calculated from digitalized X-ray scan. The Knee Roll software was made for this purpose. RESULTS The extension of the knee in non-weight loaded and weight loaded conditions is a combination of rolling and sliding joint surface motion with 6:5 ratio, in both genders. During the last 20 degrees of the extension of weight loaded male knee, rolling/sliding ratio changed to 8:1 (P<0.05). Average radii of condylar curves were between 4.5 and 1.7 cm medially, and between 3.2 and 1.8 cm laterally, for 0 degrees and 90 degrees flexion contact point, respectively. Gender differences in the radii of condylar curves, after the adjusting to body height were insignificant. CONCLUSION A higher proportion of joint surface sliding with consecutive anterior tibial displacement in women indicates more strain during knee extension, potentially making the female anterior cruciate ligament tend and susceptible to injury. The gender differences in the knee kinematics are probably the consequence of different soft tissue structure or its activity, because no difference in the sagittal shape of femoral condyles was noted.