Effect of Nearly Isometric ACL Reconstruction on Graft-Tunnel Motion: A Quantitative Clinical Study

Background: In anterior cruciate ligament (ACL) reconstruction, minimizing the graft-tunnel motion (GTM) will promote graft-to-bone healing and avoid graft loosening or tearing as well as potential bone tunnel enlargement. A nearly isometric state of the graft can be achieved by placing the tunnel properly to theoretically gain better graft-to-bone healing. However, little clinical evidence is available to quantify the relation between GTM and tunnel position. Purpose: To find the proper zones for the femoral and tibial tunnel apertures that minimize the GTM, referred to as the “nearly isometric zone,” through use of intraoperative GTM measurement and 3-dimensional computed tomography (3D-CT). Study Design: Cross-sectional study; Level of evidence, 3. Methods: A total of 100 patients were enrolled in this study. Nearly isometric ACL reconstruction was performed, and an intra-articular GTM measuring device was designed to measure and record the amplitude of GTM while the knee was flexed from 0° to 120°. Postoperatively, the patients underwent multislice CT, and the images were used to create 3D-CT models. After tibial aperture examination, 5 patients were excluded due to the divergence of tibial aperture, and therefore 95 patients remained in the study. Patients were divided into 2 groups according to whether the lateral intercondylar ridge was absent or present. The Bernard-Hertel grid coordinates ( h, t) of the femoral tunnel were then quantified. Results: The maximal GTM (mGTM) was a mean ± SD of 1.06 ± 0.66 mm (range, 0.0-3.0 mm). The mGTM in patients with a lateral intercondylar ridge was significantly lower than that in patients without a lateral intercondylar ridge (0.81 ± 0.39 vs 1.59 ± 0.73 mm, respectively; P < .0001). The average h and t were 0.227 ± 0.079 and 0.429 ± 0.770, respectively. Notably, in 1 patient, the mGTM was 0 mm whereas the coordinates ( h, t) of the femoral tunnel were 0.250 and 0.255. The overall GTM slowly increased before 90° but increased significantly after the knee was bent 105° ( P = .010). Correlation analysis showed that the t coordiinate had significant correlation with mGTM ( R = 0.581; P < .001). A gradient pattern was created to show the nearly isometric blue zone (mGTM <0.5 mm), which was found to overlap with the IDEAL (isometric, direct insertion, eccentric, anatomic, low tension-flexion pattern) position. Conclusion: A method of measuring intraoperative GTM and quantifying femoral tunnel position on postoperative 3D-CT was successfully developed. The presence of a lateral condylar ridge can significantly reduce mGTM. A nearly isometric zone was described that was consistent with the IDEAL concept.

Positioning of the femoral tunnel in anterior cruciate ligament reconstruction: functional anatomical reconstruction

The aim of this study was to review and update the literature in regard to the anatomy of the femoral origin of the ACL, the concept of the double band and its respective mechanical functions, and the concept of direct and indirect fibres in the ACL insertion. These topics will be used to help determine which might be the best place to position the femoral tunnel and how this should be achieved, based on the idea of functional positioning, that is, where the most important ACL fibres in terms of knee stability are positioned. Low positioning of the femoral tunnel, reproducing more of the posterolateral band, and positioning the tunnel away from the lateral intercondylar ridge, that is, in the indirect fibres, would theoretically rebuild a ligament that is less effective in relation to knee stability. The techniques described to determine the femoral tunnel’s centre point all involve some degree of subjectivity; the point is defined manually and depends on the surgeon’s expertise. The centre of the ACL insertion in the femur should be used as a parameter. Once the centre of the ligament in its footprint is marked, the centre of the tunnel must be defined, drawing the marking toward the intercondylar ridge and anteromedial band. This will allow the femoral tunnel to occupy the region containing the most important original ACL fibres in terms of this ligament’s function.