Three-Dimensional Reconstruction Computed Tomography Evaluation of the Tunnel Location and Angle during Anatomic Single-Bundle Anterior Cruciate Ligament Reconstruction: A Comparison of the Anteromedial Portal and Outside-In Techniques

PURPOSE: Tibial tunnel-independent drilling has attracted increased interest in recent years for anatomic anterior cruciate ligament (ACL) reconstruction. The purpose of this study was to compare the geometry and position of the femoral tunnel between the anteromedial portal (AMP) and outside-in (OI) techniques after anatomic single-bundle ACL reconstruction. METHODS: We prospectively evaluated 82 patients undergoing single-bundle ACL reconstruction with hamstring tendon autografts using either the AMP (n=40) or OI (n=42) technique. The locations of the tibial and femoral tunnel apertures were assessed by immediate postoperative 3-dimensional computed tomography (3D CT) imaging with OsiriX imaging software. The femoral graft bending angle, femoral tunnel aperture shape (height/width ratio), femoral tunnel length, and posterior wall breakage were also measured. RESULTS: The two techniques did not differ significantly in the femoral tunnel position perpendicular to the Blumensaat line. However, the mean femoral tunnel position parallel to the Blumensaat line was more caudally positioned in the AMP group than in the OI group (P=0.025) The two groups did not differ significantly in tibial tunnel position. The mean femoral tunnel length did not differ between the AMP (36.1±0.33 mm) and OI groups (35.6±0.37 mm; P=0.548) The mean femoral graft angle in the OI group (99.6°±7.1°) was significantly more acute than that of the AMP group (108.9°±10.2°) (p < 0.0001). The mean height/width ratio of the AMP group (1.21±0.20) was significantly more ellipsoidal than that of the OI group (1.07±0.09) (p < 0.0001). Posterior wall breakage was detected in 3 cases (7.5%), all in the AMP group. CONCLUSIONS: After single-bundle anatomic ACL reconstruction, 3D CT showed a significantly shallower femoral tunnel in the AMP group than in the OI group. The AMP group had a more ellipsoidal femoral tunnel with a risk of posterior wall breakage than the OI group. The OI group showed a more acute bending angle of the femoral tunnel than the AMP group.