Summary

The virtual triple-bundle ACL graft on the 3-D CT via the femoral tunnels created behind the resident’s ridge showed the equivalent orientation to the normal ACL on MRI.

Abstract

Purpose

We have been adopting the bony landmark strategy (BLS) to delineate the anterior
cruciate ligament (ACL) attachment areas in the anatomical triple-bundle ACL reconstruction. The aim of this study was to scrutinize femoral tunnel position to closely mimic the normal ACL in the ACLR.

Methods

3-D CT and MRI were obtained in 14 normal knees in full extension. Two types of virtual triple bundle ACL grafts (VACL) with different femoral tunnel positions were compared. 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 BLS (BR-VACL group). In the other type, the tunnels were placed on the RR (OR-VACL group). VACL was displayed as 3 straight lines by connecting the 2 centers of the femoral attachment areas of AM and PL to those of the 3 tibial footprints of AMM, AML and PL attachments on 3-D CT, and then superimposed on MRI. The location of the attachment position of each bundle of BR-VACL and OR-VACL was evaluated using the quadrant method on 3-D CT images. Then, the ACL/ACL graft-the tibial plateau (ACL-TP) angles were compared among normal ACL (N-ACL), BR-VACL and OR-VACL.

Results

The femoral tunnels of BR-VACL were located at 13.6 ± 2.5% / 22.1 ± 9.0% for the AM and 25.3 ± 3.1% / 52.4 ± 7.0% for the PL in deep-shallow / high-low directions by the quadrant coordinate system. On OR-VACL, they were located at 24.9 ± 2.8% / 30.5 ± 3.6% for the AM and 37.2 ± 4.2% / 59.3 ± 3.9% for the PL. Thus, the femoral tunnels of the BR-VACL were significantly deeper and higher compared to those of the OR-VACL in both AM and PL, showing the tunnels for the BR-VACL was much closer to the ideal tunnel position determined by the quadrant technique.
The mean ACL-TP angles of N-ACL, BR-VACL and OR-VACL 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. Those on the oblique-sagittal slices were 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, respectively. There was no significant difference in the angles between N-ACL and BR-VACL, while those of AMM and PL in OR-VACL were significantly narrower compared to N-ACL.

Conclusion

(1) The virtual triple-bundle ACL graft on the 3-D CT via the femoral tunnels created behind the resident’s ridge showed the equivalent orientation to the normal ACL on MRI. (2) The bony landmark strategy is useful to create anatomical tunnels at the time of ACLR.