This study aimed to investigate the correlation between a higher lateral tibial slope (LTS) and inferior subjective outcomes following single-bundle anterior cruciate ligament (ACL) reconstruction over an extended period. Our findings support the theory that a greater LTS is associated with poorer subjective outcomes post-single-bundle ACL reconstruction in the long term. Our statistical evaluation also indicates that gender influences patient subjective outcomes, with females experiencing less favorable results.
Webb et al. has found that the slope of the lateral tibial plateau may be a more sensitive risk factor for ACL injuries than the medial tibial plateau. [38] Prior studies have investigated the link between the lateral tibial slope (LTS) and the risk of graft failure after anterior cruciate ligament reconstruction (ACLR).[26, 27, 39–41] These studies have suggested a range of LTS cutoff values to distinguish between groups at higher risk for graft failure and those at lower risk.[26, 27, 42, 43] However, the conclusions drawn from these studies vary, a discrepancy that can be attributed to the different methods employed in measuring LTS. In a 2019 case-control study, Grassi et al. investigated 43 patients who experienced graft failure after primary anterior cruciate ligament reconstruction (ACLR).[27] They identified a lateral tibial slope (LTS) cutoff point of 7.4 degrees as a potential indicator of increased risk for graft failure. However, the specific surgical techniques used in these ACLR procedures were not detailed in their study. Additionally, it's important to note that Grassi et al. employed a different methodology for measuring tibial slopes on MRI scans, which could influence the outcomes and comparability of their results. In a separate study, Cooper et al. focused on a larger cohort, enrolling 634 patients who had undergone primary single-bundle ACLR, including 317 individuals who required revision surgery and 317 who did not.[28] In this study, MRI scan measurements were performed using the technique described by Hashemi et al. One limitation of the Cooper et al. study was the lack of uniformity in graft types and femoral fixation methods used in the ACLR procedures, which could potentially affect the generalizability and interpretation of their findings. In our study, we adopted the measurement technique as described by Hashemi et al. for assessing the lateral and medial tibial slopes on MRI scans.[44] This approach allowed for a standardized and replicable method of evaluation, crucial for the reliability of our findings. Additionally, to maintain consistency in surgical variables, all patients in this study underwent single bundle anterior cruciate ligament reconstruction (ACLR) using the same graft type — hamstring tendon grafts. This consistency in both the measurement technique and surgical approach enhances the comparability of our results and provides a more controlled framework for analyzing the impact of tibial slope on post-operation ACLR subjective outcomes.
We found that an increased LTS was associated with poorer postoperative patient-reported outcome measures (PROMs), including Lysholm Knee Score, the UCLA Activity Score, the IKDC Score, and the Tegner Activity Score. This negative correlation indicates that a higher LTS may be predictive of less satisfactory outcomes following ACL reconstruction. Our findings are consistent with previous research indicating a relationship between higher LTS and increased risk of ACL injuries. Several biomechanical studies suggested that a higher LTS could increase anterior tibial translation, thereby increasing strain on the ACL. However, no previous studies had emphasized on the effect of increased tibial slope towards patient subjective outcomes. Our results suggest that the increased strain resulting from higher LTS could indeed impact the postoperative recovery and subjective outcomes following ACL reconstruction. This insight adds to our understanding of the complex interplay between biomechanical factors and patient-reported outcomes in the context of ACL injuries and reconstruction surgery.
While some studies suggest that double-bundle ACL reconstruction restores greater knee stability with respect to the antero-posterior and rotational stability than a single-bundle reconstruction, others have indicated that a single-bundle ACL reconstruction is sufficient to restore normal joint laxity.[45, 46] Our study recognizes the widely varied opinions and results between the difference in prognosis in single and double bundle ACL reconstruction. To provide a more targeted and controlled analysis, our research exclusively included patients who underwent single-bundle ACL reconstruction. This focused approach enables us to specifically investigate the prognosis and outcomes associated with this technique, thereby contributing valuable insights. By isolating this variable, our study aims to offer a clearer understanding of the correlation of LTS and subjective outcomes following single-bundle reconstruction.
Regarding the prognosis following anterior cruciate ligament (ACL) reconstruction between sexes, previous studies have demonstrated poorer outcomes in female patients compared to their male counterparts. [47–49] Females have inferior outcomes in instrumented laxity, revision rate, and activity scale after ACL reconstruction compared to males, but both sexes show comparable outcomes in other tests including anterior drawer test, Lachman test, pivot-shift test, timed single-legged hop test, single-legged hop test, quadriceps testing, hamstring testing, extension loss, flexion loss, development of cyclops lesion, and International Knee Documentation Committee (IKDC) knee examination score. [48] Some studies, however, found no difference in prognosis between sexes after ACL reconstruction surgery.[50, 51] Our study provides further evidence to support the gender disparity in ACL reconstruction results. In our cohort, female patients exhibited less favorable long-term PROMs and a statistically significant steeper lateral tibial slope (LTS), both of which are noteworthy factors contributing to the overall prognosis.
Furthermore, the established cut-off value of LTS in our study was 8.35 degrees, which was the point of distinction between patients with "Good" and "Fair" Lysholm scores. Previous studies have established varying cut-off values distinguishing better and inferior outcomes.[26] Webb et al. concluded that a posterior tibial slope (PTS) of above 12° had the most pronounced risk for ACL graft failure[38]. Grassi et al. established a cut-off value of 7.4° as an indicator for graft failure.[27] Gupta et al. found that an increased risk of graft failure was most evident with a posterior tibial slope (PTS) ≥ 10°, while Jaecker et al. observed similar findings for a lateral tibial posterior slope (LTPS) ≥ 10°.[11, 52] It is important to note that these studies exhibit variations to their methodologies, including patient selection, measurement techniques, and analysis, which can influence the interpretation and comparability of their results. Our study was designed to control for various variables, including hamstring grafts, single bundle surgical techniques, and the Hashemi measurement method, to ensure the reliability of our findings. However, our established cut-off value of LTS should nonetheless be interpreted with caution as LTS can still vary significantly among individuals and may be influenced by several factors, such as sex, age, and ethnicity.
Limitation
Our study has several limitations. Firstly, the study was retrospective in nature, which could lead to potential selection biases that could affect the results. Additionally, the study was limited to a single institution, which could limit the generalizability of the results. Furthermore, arthrometer examination were not included in our study. GNRB arthrometer was not applied as part of our institution protocol for ACL injury patients until 2019. Finally, future study with larger sample sizes is needed to validate our findings and further explore the influence of LTS on ACL reconstruction outcomes.