Greater Static Anterior Tibial Subluxation of the Lateral Compartment After an Acute Anterior Cruciate Ligament Injury Is Associated With an Increased Posterior Tibial Slope.

Background: Static anterior tibial subluxation of the lateral compartment after an anterior cruciate ligament (ACL) injury highlights an increased anterior position of the tibia relative to the femur. However, the precise cause of this phenomenon is not entirely clear. Recently, an increased posterior tibial slope (PTS) has been identified as an independent risk factor for noncontact ACL injuries. Hypothesis: An increased PTS is associated with an increased anterior position of the lateral compartment of the tibia relative to the femur after acute ACL injuries. Study Design: Case-control study; Level of evidence, 3. Methods: From March 2016 to March 2017, a total of 154 patients with clinically diagnosed noncontact ACL injuries who underwent primary ACL reconstruction were retrospectively analyzed. Static anterior subluxation of the lateral compartment relative to the lateral femoral condyle was measured on preoperative magnetic resonance imaging. Among them, 23 patients (study group) who demonstrated >= 6-mm anterior subluxation of the lateral compartment were matched in a 1: 1 fashion to 23 control participants (control group), who showed <6-mm anterior subluxation of the lateral compartment. The PTS was measured on routinely available preoperative weightbearing lateral knee radiographs. Predictors of increased (>= 6 mm) static anterior subluxation of the lateral compartment, including body mass index (BMI), PTS, injuries to the anterolateral ligament (ALL), and concomitant lateral meniscal lesions, were assessed by multivariable conditional logistic regression analysis. Results: The mean PTS in the study group was 15.4 degrees, which was significantly larger than that in the control group (degrees 8.8) (P <. 001). In addition, an abnormal degree of PTS (>= 10.0 degrees) was determined to be an independent risk factor (odds ratio, 8.0 [95% CI, 2.729.2]; P < . 001) associated with >= 6-mm anterior subluxation of the lateral compartment after acute ACL injuries. However, BMI, presence of concomitant lateral meniscal lesions, and presence of ALL ruptures were not. Conclusion: An increased PTS was identified to be an independent anatomic risk factor of increased (>= 6 mm) anterior subluxation of the lateral compartment in acute noncontact ACL injuries. For patients with obviously increased anterior tibial subluxation of the lateral compartment after ACL injuries, the PTS should be measured.