Summary

We successfully located a true femoral tunnel point for isometric-like ACL reconstruction.

Abstract

Background. In ACL reconstruction, Once the reconstructed graft is not in isometric-like, poor graft-bone healing, graft loose and potential bone tunnel enlargement may happen due to graft-tunnel motion (GTM) such as the effect of bungee cord or windshield wiper. However, there is still no way to ensure a successful isometric-like reconstruction to achieve better healing outcome. So we managed to perform a prospective study in order to find the true ACL isometric-like tunnel position on the lateral femoral condyle.

Method. 100 consecutive initial ACL injury patients were included in our prospective study. ACL reconstruction was performed with use of a hamstring autograft in suspensory fixation technique by a single surgeon. The intra-articular part of the graft was marked with suture knots, one and the other at the tibial and femoral tunnel aperture, the third at the middle point between the previous two. The tibial tunnel was drilled in the middle of the arm of the C-shape ACL remnant. In early stage, the femoral tunnel was drilled on the cross point of the lateral intercondyle ridge and the bifurcate ridge (Point A). Later, it moved above and posteriorly (Point B). After the reconstruction was finished, we use an intra-articular GTM measuring device to measure the amplitude of GTM while the knee was flexed. After the surgery, the patient received a multi-slice computer tomography (MSCT) to locate the intra-articular tibial and femoral tunnel point through 3D reconstruction. Bernard-Hertel grid was used to quantify the coordinates (h, t) of the femoral tunnel. While a rectangle coordinate system was used to quantify the coordinates (a, b) of the femoral tunnel. Statistical correlation analysis was proceed to evaluate the data.

Results. The cases were male dominant (90 males and 10 female) and the average age was 27.1±8.4 years old. 58 surgeries were performed on the left side while 42 on the right side. The graft type usage was distributed as 30 on allograft, 50 on autograft and 20 on synthetic graft. The average maximal GTM was 1.14±0.68mm (0-3mm). The average (a, b) was (0.45±0.02, 0.50±0.01) so that all the cases showed high consistency on tibial tunnel aperture position. The average (h, t) on the femoral tunnel aperture position was (0.23±0.08, 0.43±0.77). The parameter t showed significant positive correlation with maximal GTM (R=0.62, P<0.0001). According to the different stage of choosing the femoral tunnel aperture, the cases were divided into group A (n=45) and group B (n=55). Both groups showed no significant differences on demographic data and surgical details. The average (h, t) of group A and group B was (0.25±0.12, 0.48±0.13) and (0.24±0.08, 0.36±0.15), respectively. Parameter t was found statistically different between 2 groups. Meanwhile, the maximal GTM of group A (1.65±1.25mm) was significantly higher than group B (0.56±0.34mm). Coordinate (0.24, 0.36) was assumed as the ideal isometric-like point. The distance between all of the femoral tunnel coordinates and the ideal isometric-like point were calculated that showed positive correlation with maximal GTM (R=0.587,P<0.0001).

Conclusion. We successfully proved that the maximal GTM is decided by femoral aperture position with a constant tibial aperture. Point B shows more graft isometry than Point A. The ideal isometric-like point is (0.24, 0.36) that is slightly above and posterior to the cross point of the lateral intercondyle ridge and the bifurcate ridge. Certain positioning surgical tool should be developed in order to facilitated more precise isometric-like ACL reconstruction.