Paper 208: The Use of 3-D CT Scan to Validate the Position of the Femoral Tunnels in Anatomic Double-bundle ACL Reconstruction

Abstract

The success of anatomic double-bundle ACL reconstruction is strongly related to tunnel positioning. Quantification and validation of tunnel location is still subject to debate. We performed a clinical study for evaluating the positioning of femoral anteromedial (AM) and posterolateral (PL) tunnels following anatomic double-bundle ACL reconstruction using high-speed 3-D computed tomography (3-D CT). We hypothesize that the position of the tunnels drilled with a specifically designed aimer will be located within the native ACL femoral footprint limits. case controlled series anatomic double-bundle ACL reconstruction with hamstrings tendons was performed with the Anatomic Director instruments set. During surgery the centre of each bundle was marked with a thermal probe. After drilling the AM tunnel through the AM portal, the PL tunnel was drilled with a specific PL aimer inserted through a far medial portal in the previously drilled AM tunnel. Thirty five continuous patients were enrolled in the study and prospectively evaluated with high speed 3-D CT scan performed within 1–3 days following surgery. Three-D reconstructions of both intact and involved knees were performed using the volume rendering technique, with the contralateral knee as control. In the control group, we measured the angle formed between the resident's ridge -which is parallel to the longitudinal axis of the ACL footprint- and the axis of the femoral diaphysis, named the “footprint angle” (FA) and the angle formed between the ridge and the Blumensaat's line (FB). On the involved side, using the axis passing through the centres of both tunnels as a reference line, FA and FB angles were also measured. The AP- and proximo-distal diameters of the ACL attachment area were measured. Also, in the involved side, the distances of ACL from the anterior, posterior and distal cartilage borders were measured and compared with the results of anatomical studies available in the literature. Finally, the distance from the centres and the bone bridge between the tunnels were also measured. the morphometric data for the involved group were the following: FA 31.4° ± 15.2°, FB 67.0° ± 16.9°, AP footprint diameter (mm) 17.2 ± 2.1, proximo distal diameter 8.1 ± 0.9, distances to cartilage (mm), posterior 2.2 ± 1.6, anterior 1.1 ± 0.7, distal 2.7 ± 1.2, distance between AM and PL bundle centres (mm) 9.4 ± 1.2. For the control group, FA 26.5° ± 4.7°, FB 61.6° ± 6.8°, AP footprint diameter (mm) 17.3 ± 1.7, proximo distal diameter 8.8 ± 1, distances to cartilage (mm), posterior 2.5 ± 1.1, anterior 1.8 ± 1.3, distal 2.8 ± 1.5, distance between AM and PL bundle centres (mm) 8.2 ± 1.2. There was no significant difference between the different values of the two groups. The native and reconstructed footprints were always entirely located distal to the resident's ridge. A highly significant correlation was found between FA and FB in both control (r = 0.71) and involved (r = 0.9) groups. The bone bridge thickness between the tunnels was 2.9mm ± 1.1mm. the morphometry of the femoral footprint of the ACL can be quantified using both its orientation and distances with regard to the local anatomical bony ridges, and cartilage borders landmarks. Locating the tunnels within the ACL footprint limits with appropriate restoration of the angle between the long axis of the femur and the long axis of the ACL femoral footprint are appropriate criteria to validate the proper positioning of the femoral tunnels when an anatomic double-bundle ACL reconstruction is performed. The use of a specifically-designed posterolateral femoral aimer allows duplicating the true morphometry of the native ACL footprint. Finally, as FA and FB are highly correlated, it is possible to use FB only to validate the footprint orientation on regular X-ray lateral view.