Association Between Secondary ACL Injury and Tibial Spine Height After Primary ACL Reconstruction: A Case-Control Study.

Background: The anterior cruciate ligament (ACL) is essential for knee stability, and reconstruction aims to restore functionality. High secondary ACL injury rates after primary ACL reconstruction (ACLR) pose significant clinical, public health, and economic challenges. Although tibial spine height (TSH) has been identified as a risk factor for primary ACL injuries, its role in secondary ACL injury after primary ACLR remains poorly understood. Purpose: To investigate whether the increase in TSH between pre- and postoperative MRI measurements is associated with secondary ACL injury after primary ACLR. Study Design: Case-control study; Level of evidence, 3. Methods: A case-control study was conducted at a single institution, including 32 patients who underwent revision surgery after noncontact secondary ACL injury and 107 patients who maintained intact ACL grafts without revision after primary ACLR during a minimum 2-year follow-up period. The primary outcome was the increase in TSH between pre- and postoperative MRI scans. Logistic regression was used to examine the association between the increase in TSH and secondary ACL injury, and the area under the receiver operating characteristic (ROC) curve (AUC) was calculated to assess the model's discriminative ability. Other imaging characteristics and anteroposterior instability using KT-2000 were analyzed. Results: Each 1-mm increase in postoperative medial TSH (MTSH) was associated with secondary ACL injury (adjusted odds ratio, 7.62; 95% CI, 3.80-18.55; P = .0001). This increase in MTSH (postoperative value minus preoperative value) suggests potential bony changes after ACLR that may be associated with secondary ACL injury risk. Additionally, the notch width index was smaller in the secondary ACL injury group compared with the control group. The increase in MTSH demonstrated strong diagnostic potential for predicting secondary ACL injury using a threshold value derived from our ROC analysis. Specifically, the AUC of 0.93 ± 0.034 indicates the model's ability to discriminate between patients who developed secondary ACL injury and those who maintained intact ACL grafts based on the increase in MTSH. Conclusion: This study demonstrates a significant association between increased MTSH and secondary ACL injury after primary reconstruction. Using a 1-mm increase in MTSH as the cutoff value, our model showed excellent discriminative ability in predicting secondary ACL injury (AUC, 0.93; 95% CI, 0.86-0.99; sensitivity, 77.42%; specificity, 98.13%). These findings suggest that evaluating after reconstruction MTSH changes, particularly increases of ≥1 mm, may serve as a valuable risk assessment tool for secondary ACL injury.