Sex-based differences in the tensile properties of the human anterior cruciate ligament

After immense amounts of research, the root cause for the significantly higher rates of anterior cruciate ligament (ACL) failure incidents in females as compared to males still remains unknown and the existing sex-based disparity has not diminished. To date, the possibility that the female ACL is mechanically weaker than the male ACL has not been directly investigated. Although it has been established in the literature that the female ACL is smaller in size, the differences in the structural and material properties of the ACL between sexes have not been studied. The aim of this cadaveric study was to determine if any sex-based differences in the tensile properties of the human ACL exist when considering age as well as ACL and body anthropometric measurements as covariates. Ten male and 10 female unpaired cadaveric knees (mean age 36.75 years) were used for this study. The geometry of the ACL (including length, cross-sectional area, and volume) was analyzed using a 3-D scanning system. The femur-ACL tibia complex was tested to failure along the longitudinal axis of the ligament in a tensile testing machine. The structural properties of the ACL as well as its mechanical properties were determined. Analysis of covariance was performed to assess the effect of sex on tensile properties. The female ACL was found to have a lower mechanical properties (8.3% lower strain at failure; 14.3% lower stress at failure, 9.43% lower strain energy density at failure, and most importantly, 22.49% lower modulus of elasticity) when considering age, ACL, and body anthropometric measurements as covariates.