Sex-Specific Associations Between Body Mass Index and Knee Flexion Kinematics and Kinetics in Individuals With Anterior Cruciate Ligament Reconstruction.

Context: Anterior cruciate ligament reconstruction (ACLR) is a common surgical procedure after injury. However, ACLR contributes to aberrant biomechanical movement patterns that influence secondary injury or joint degeneration. Higher body size may influence gait and landing biomechanics differently between males and females. The purpose of this study was to investigate the influence of sex on the association between body mass index (BMI) and knee biomechanics long-term after ACLR recovery.

Design: Sixteen female (BMI: 27.7 [5.4]) and 14 male (BMI: 24.2 [5.5]) participants who had a history of ACLR performed walking and drop vertical jump tasks.

Methods: The knee-flexion angle (KFA), external knee flexion moment, knee abduction moment (landing), and knee adduction moment (gait) were measured using 3D motion capture. Body fat percentage was assessed using a BOD POD. Moderated regression evaluated the influence of sex on the association between BMI and biomechanical outcomes after adjusting for body fat percentage.

Results: There was a significant interaction between sex and BMI on the KFA at heel contact (P = .01), peak KFA (P = .04), and peak external knee flexion moment (P = .05) during gait and on the KFA at ground contact during landing (P = .04). Higher BMI was associated with smaller KFAs at heel contact (P = .03), smaller peak KFAs during gait (P = .02), and smaller external knee flexion moments (P = .01) but only in females. Similarly, a higher BMI was associated with a smaller KFA at ground contact during landing (P = .03) but only in females. There was no sex by BMI interaction on the knee adduction moment during gait (P = .657) or on the knee abduction moment during landing (P = .643). Moreover, sex and BMI were not independent predictors of the knee adduction moment during gait or the knee abduction moment during landing (all P > .05).

Conclusions: The association between sex and BMI may have implications for posttraumatic knee osteoarthritis and ACL reinjury, and female sex and high BMI should be considered when designing individualized rehabilitation programs. These findings suggest that females with high BMI may benefit from interventions to improve knee flexion during landing and gait.