Is posterior tibial slope associated with noncontact anterior cruciate ligament injury?

This study aimed to: (1) examine whether the association between posterior tibial slope and noncontact ACL injury exists in Chinese population; (2) compare the reliability and consistency of the three methods (longitudinal axis, posterior and anterior tibial cortex axis) in lateral radiograph. Case-control study contained 146 patients in total (73 noncontact ACL injuries and 73 meniscus injuries, matched for age and gender), which were verified by arthroscopy, MRI and physical examination. For the total population and the male subgroup, the mean posterior tibial slope of the ACL-injured group was significantly higher than that of the control group (P < 0.001). In addition, the longitudinal axis method exhibited the highest inter-rater (0.898) and intrarater reliability (0.928), whereas the anterior tibial cortex was the most variable (inter-rater reliability, 0.805; intrarater reliability, 0.824). The anterior tibial cortex method produced largest posterior tibial slope measurements (13.8 +/- A 3.3 for injury group; 11.6 +/- A 2.7 for control group), while the posterior tibial cortex method was the smallest (9.1 +/- A 3.1 for injury group; 7.2 +/- A 2.6 for control group). All three methods were not affected by age, sex, height, weight and BMI (n.s.). The results of this study suggested that an increased posterior tibial slope was associated with the risk of noncontact ACL injury in Chinese population. Meanwhile, the longitudinal axis method is recommended for measuring posterior tibial slope in lateral radiograph in future studies. Posterior tibial slope measured by longitudinal axis method may be used as predictor of ACL injury. Case-control study, Level III.