Anterior Cruciate Ligament-Injured Subjects Have Smaller Anterior Cruciate Ligaments Than Matched Controls A Magnetic Resonance Imaging Study

Background: Very few studies examining the predisposing anatomical factors leading to anterior cruciate ligament (ACL) injuries have examined the ACL itself, and none of these directly examined the difference in ACL properties between injured and matched control subjects. Hypothesis: The ACL total volume in people who have experienced a noncontact ACL injury is smaller than that of matched controls. Study Design: Case control study; Level of evidence, 3. Methods: Contours of the ACL were manually identified in sagittal magnetic resonance images, and volumes were calculated for 27 contralateral, healthy knees of individuals after noncontact ACL injury and for 27 control subjects matched for gender, height, age, and weight. Validation of this method was performed on 5 porcine knees. Stepwise multiple regression was used to determine the difference in ACL volume between injured and control subjects while considering gender, height, weight, and age as potential covariates. Results: Contralateral ACL volume for injured subjects was significantly smaller than for noninjured subjects (P = .0208) by 231 mm(3) after adjusting for weight, which was also a significant contributor to ACL volume (P < .0001). At the average body mass of 72.7 kg, subjects with a noncontact ACL injury had an average contralateral ACL volume of 1921 mm(3), while the corresponding control group had an average volume of 2151 mm(3). Gender, height, and age were not significant when weight was included in the regression model. Conclusion: This study shows that there are anthropometric differences between the knees of subjects with a noncontact ACL injury and those without an ACL injury, suggesting that ACL volume may play a direct role in noncontact ACL injury.