The Relationship Between Posterior Tibial Slope and Anterior Cruciate Ligament Injuries

Background: Two previous studies have examined the association between an increased posterior tibial slope and anterior cruciate ligament (ACL) injuries as measured on plain radiographs. The study results were contradictory, with 1 reporting a statistical difference and the other showing no association. Purpose: To determine if there is a difference in posterior tibial slope angle between patients with a history of noncontact ACL injury and a control group with no history of ACL injury. A secondary objective was to examine differences in tibial slope angle between male and female subjects within each group. Study Design: Case-control study; Level of evidence, 3. Methods: We identified all noncontact ACL injuries that were treated operatively at the United States Military Academy, West Point, New York, from 2004 to 2007. We digitally measured the posterior tibial slope from plain film radiographs of 140 noncontact ACL injuries, stratified them by sex, and compared them with a control cohort of 179 patients and radiographs. Results: Subjects in the noncontact ACL group had significantly greater slope angles (9.39 degrees +/- 2.58 degrees) than did control subjects (8.50 degrees +/- 2.67 degrees) (P = .003). The trend toward greater tibial slope angles in the noncontact ACL group was also observed when each sex was examined independently; however, the difference was only statistically significant for the female subjects between the injury and control groups (9.8 degrees +/- 2.6 degrees vs 8.20 degrees +/- 2.4 degrees) (P = .002). Conclusion: Despite the identification of an increased posterior tibial slope as a possible risk factor for women, more research that combines the multifactorial nature of an ACL injury must be performed.