Virtual triple-bundle ACL graft via femoral tunnels behind the resident's ridge on 3D CT demonstrates equivalent orientation to native ACL

Purpose: To clarify the femoral tunnel location for a virtual anterior cruciate ligament (ACL) graft to simulate the native ACL.

Methods: Three-dimensional (3D) computed tomography (CT) and magnetic resonance imaging (MRI) were obtained in 14 normal knees in full extension. Two types of virtual triple bundle ACL grafts (VACLG) were created. In one type, the femoral tunnels for anteromedial bundle (AM = AMM/anteromedial bundle medial part + AML/anteromedial bundle lateral part) and posterolateral bundle (PL) were positioned behind the resident's ridge (RR) based on the bone landmark strategy (BR-VACLG group). In the other type, the tunnels were placed on the RR (OR-VACLG group). VACLG was displayed as three straight lines by connecting the two centres of the femoral attachment areas of AM and PL to those of the three tibial footprints of AMM, AML and PL attachments on 3D CT, and then superimposed on MRI. The ACL/ACL graft-the tibial plateau (ACL-TP) angles were compared among normal ACL (N-ACL), BR-VACLG and OR-VACLG.

Results: The mean ACL-TP angles of N-ACL, BR-VACLG and OR-VACLG were 74.4 ± 3.4°, 75.2 ± 4.5° and 68.7 ± 5.0° for AMM, 81.9 ± 3.8°, 82.9 ± 5.1° and 76.3 ± 4.0° and for AML, 71.1 ± 6.4°, 70.0 ± 7.2° and 61.0 ± 4.7° for PL on the oblique-coronal slices; 55.3 ± 4.9° 53.9 ± 4.4° and 50.5 ± 4.3° for AMM; 54.9 ± 4.5°, 54.7 ± 2.6° and 50.7 ± 3.2° for AML; 51.4 ± 3.3°, 51.2 ± 2.4° and 48.1 ± 2.0° for PL on the oblique-sagittal slices. There was no significant difference in the angles between N-ACL and BR-VACLG, while those of AMM and PL in OR-VACLG were significantly lower compared to N-ACL.

Conclusion: The virtual triple bundle ACL graft via femoral tunnels behind the RR on 3D CT shows equivalent orientation to the native ACL on MRI in full extension.

Level of evidence: Level III.