Correlation of Increased Lateral Tibial Slope With Baseline Tibial Position in Intact Knees and Side-to-Side Anterior Tibial Translation for Knees With ACL Tears

Background: Anterior cruciate ligament (ACL) stress techniques—including single-leg stress radiographs, Telos, and KT-1000 arthrometer—are highly accessible and can provide additional diagnostic information to assess ACL and ACL graft integrity. The degree of anterior tibial translation (ATT) may be useful in guiding treatment when a diagnosis on magnetic resonance imaging is not conclusive or for judging if additional treatments, such as anterolateral complex augmentation, may be necessary. Purpose/Hypothesis: The purpose of this study was to evaluate the effect of increasing posterior tibial slope (PTS) on baseline tibial position (BTP) and side-to-side differences (SSD) in ATT. A secondary purpose was to perform a subgroup analysis of SSD in ATT for patients with a PTS of ≥12° versus <12°, as well as for acute (<6 weeks from injury) versus chronic (≥6 weeks from injury or ACL graft tear) ACL tears. It was hypothesized that the BTP in normal intact knees would increase linearly with the PTS and there would be an increased SSD in ATT when comparing ACL-injured and ACL-intact knees. Study Design: Case-control study; Level of evidence, 3. Methods: Bilateral ACL stress radiographs were assessed from patients with primary ACL and ACL graft tears between March 2023 and March 2024. Bilateral stress views were obtained by single-leg full-length lateral weightbearing radiograph in 20° of knee flexion. The BTP and ATT were measured using a perpendicular line drawn between the posterior position of the lateral femoral condyle and the lateral tibial plateau. PTS measurements were assessed by the anatomic tibial axis. Statistical analysis using linear regression— r > 0.6 was considered strong, r between 0.4 and 0.6 moderate, and r < 0.4 weak—and t tests were used to compare the PTS with BTP and SSD in ATT. Results: A total of 72 patients were analyzed using ACL stress radiographs. The results found a significant positive correlation between increased PTS and increased BTP for the ACL-intact knees ( P < .001; r = 0.476). A significant increase was found in the SSD in ATT of 1.73 mm with a positive correlation between increased PTS and increased SSD in ATT of ACL-deficient knees ( P < .001; r = 0.397). A subgroup analysis reported significant increases in SSD in ATT for both ACL-injured knees with a PTS ≥12° ( P = .008) and for chronic ACL tears ( P < .001) and no significant differences in SSD in ATT for ACL-injured knees with a PTS of <12° ( P = .650) and for acute ACL tears ( P = .745). Conclusion: This study found a significant positive correlation between PTS and the BTP in ACL-intact knees and for the SSD in ATT between ACL-injured and ACL-intact knees. Moreover, the SSD in ATT was significantly increased for ACL-injured knees with a PTS of ≥12° and for chronic ACL tears. No significant difference in SSD in ATT was found for ACL-injured knees with a PTS of <12° and for acute ACL tears.