Notch-referenced mediolateral verification of tibial tunnel position in anterior cruciate ligament reconstruction: a 3D imaging validation study

BACKGROUND: Non-anatomic tibial tunnel placement remains a leading contributor to anterior cruciate ligament reconstruction (ACLR) failure. Mediolateral (ML) tunnel positioning is particularly difficult intraoperatively because no consistent bony landmark defines the lateral footprint border. PURPOSE: To evaluate the accuracy of a novel intraoperative Notch-Referenced Mediolateral (NRML) verification technique by comparing the ML position of the tibial tunnel center (TTC) on postoperative 3D CT with the native tibial footprint center (TFC) on preoperative 3D MRI. METHODS: In this retrospective cross-sectional study, 108 consecutive patients underwent primary all-inside single-bundle ACLR with intraoperative NRML verification. This arthroscopic technique uses the intercondylar notch as a visual reference to verify mediolateral tibial tunnel position before definitive drilling. TFC and TTC were independently measured on preoperative 3D MRI and postoperative 3D CT using a standardized quadrant-grid protocol by two blinded observers. The primary outcome was ML deviation (tunnel - footprint). MRI-CT agreement and measurement reliability were assessed with intraclass correlation coefficients (ICC) and Bland-Altman analysis. RESULTS: The anatomical TFC was located at 46.1 ± 2.3% of tibial plateau width in the ML direction, versus 44.8 ± 2.0% for the TTC. Mean ML deviation was -1.01 ± 1.52 mm (p < 0.001), a small but statistically significant medial bias; 91.7% (95% CI 84.9-95.6%) of tunnels fell within ±3 mm of the native footprint. MRI-CT agreement was good (ICC 0.81-0.85), and inter/intraobserver reliability was good to excellent (ICC 0.78-0.89). No significant associations were found between ML deviation and sex, injury chronicity, graft diameter, or plateau size. CONCLUSION: In this single-arm cohort,NRML verification is a simple, equipment-free technique that placed the tibial tunnel within ~1 mm of the native ML footprint, with high measurement reliability. Prospective comparative and outcome studies are needed to confirm its clinical value. LEVEL OF EVIDENCE: IV.