Purpose

Combined anterior cruciate ligament (ACL) and extra-articular lateral reconstructions bear the risk of a tunnel conflict. The goal of the present study was to provide a surgical rationale in order to avoid this tunnel conflict. It was hypothesized that a tunnel conflict is not only dependent on the insertion site of the lateral extra-articular tenodesis (LET), but also on the flexion angle, when drilling the ACL. Furthermore, it was hypothesized that by putting the LET insertion site anterior and proximal to the lateral femoral epicondyle, the tunnel conflict rate can be reduced.

Methods

Ten fresh frozen cadaveric knee specimen were used for measurements. Several K-wires were drilled into the lateral aspect of the femoral condyle according to published LET descriptions. Femoral insertion site and drill angles were precisely aligned according to the trans epicondylar axis and the femoral shaft axis using a custom-made alignment rig and a 3D printed drill angle template. The following insertion sites were tested according to LET insertion sites: original Lemaire insertion site (8 mm proximal and 4 mm posterior to the lateral epicondyle, 30° anterior and 30° proximal angulation), anterior Lemaire insertion site (5 mm proximal and 5 mm anterior; 30° anterior and 30° proximal angulation). K-wires were then inserted into the center of the femoral ACL footprint and drilled according to a standardized anteromedial portal single-bundle reconstruction in 110° and 140° knee flexion. An ACL reconstruction at 120° and 130° knee flexion was simulated using a metrology software. K-wires were then cut at bone level and each end was digitized using a portable measuring arm (Absolute Arm Compact, Fa. Hexagon, Wetzlar, Germany) with an accuracy of +/- 0.019 mm. Angles and distances between the K-wires in the aforementioned coordinate system were then measured. Measurements were then extrapolated to an 8 mm ACL tunnel and a 6 mm LET tunnel. A mixed model was used to determine statistical significances.

Results

Knee flexion angle when drilling the ACL showed a significant effect (p < 0.001) on the tunnel conflict rate between the ACL and LET tunnel. Tunnel conflicts gradually increased (p < 0.001) when the knee was flexed from 110° to 140°, when drilling the ACL tunnel. This resulted in 32.9% (110°) and 22.1% (120°) less tunnel conflicts compared to 140°.
Similarly, the LET insertion site also had a significant effect (p < 0.001) on the tunnel conflict rate. The anterior Lemaire showed a significant (p < 0.001) lower tunnel confluence rate (40% vs. 15%) than the original Lemaire insertion point.

Conclusion

Tunnel conflict rate in simultaneous ACL reconstruction and LET is not only dependent on LET insertion site, but also on the knee flexion angle, when drilling the femoral ACL tunnel. It appears that an anterior Lemaire insertion point results in less tunnel conflicts than the original Lemaire insertion site.