Sex Comparisons of In Vivo Anterior Cruciate Ligament Morphometry

Context: Females have consistently higher anterior cruciate ligament (ACL) injury rates than males. The reasons for this disparity are not fully understood. Whereas ACL morphometric characteristics are associated with injury risk and females have a smaller absolute ACL size, comprehensive sex comparisons that adequately account for sex differences in body mass index (BMI) have been limited. Objective: To investigate sex differences among in vivo ACL morphometric measures before and after controlling for femoral notch width and BMI. Design: Cross-sectional study. Setting: Laboratory. Patients or Other Participants: Twenty recreationally active men (age = 23.2 +/- 2.9 years, height = 180.4 +/- 6.7 cm, mass = 84.0 +/- 10.9 kg) and 20 recreationally active women (age = 21.3 +/- 2.3 years, height -166.9 +/- 7.7 cm, mass = 61.9 +/- 7.2 kg) participated. Main Outcome Measure(s): Structural magnetic resonance imaging sequences were performed on the left knee. Anterior cruciate ligament volume, width, and cross-sectional area measures were obtained from T2-weighted images and normal-ized to femoral notch width and BMI. Femoral notch width was measured from T1-weighted images. We used independent-samples t tests to examine sex differences in absolute and normalized measures. Results: Men had greater absolute ACL volume (1712.2 +/- 356.3 versus 1200.1 +/- 337.8 mm(3) ; t(38) = 4.67, P < .001) and ACL width (8.5 +/- 2.3 versus 7.0 +/- 1.2 mm; t(38) -2.53, P= .02) than women. The ACL volume remained greater in men than in women after controlling for femoral notch width (89.31 +/- 15.63 versus 72.42 +/- 16.82 mm(3)/mm; t(38) = -3.29, P= .002) and BMI (67.13 +/- 15.40 versus 54.69 +/- 16.39 mm(3)/kg/m(2); t(38) =-2.47, P = .02). Conclusions: Whereas men had greater ACL volume and width than women, only ACL volume remained different when we accounted for femoral notch width and BMI. This suggests that ACL volume may be an appropriate measure of ACL anatomy in investigations of ACL morphometry and ACL injury risk that include sex comparisons.