ACL Navigation Techniques The most controversial and challenging technique in ACL reconstruction surgery is the double-bundle ACL reconstruction technique. Currently, the technical precision required for reconstructive surgery is quite high in order to obtain the mechanical stability that a double-bundle ACL reconstruction can provide. In fact, navigational surgery has been widely used in the field of orthopedics, from the first artificial joint replacements, to later spine surgery, oncology surgery and trauma surgery with success. When it comes to soft tissue surgery, such as ACL reconstruction, great challenges arise, especially in terms of how to achieve coupling and matching between clinician and engineering design. We would like to share with the attendees some of our early experiences using next-generation software during double-bundle ligament reconstruction. A tracer was placed on the tibial and femoral side, external calibration tests, applied clinical tests, Lachmann tests, torsion tests and drawer tests were performed, followed by knee kinematic evaluation. The internal image of the selected position of the tibial and femoral tunnel is observed, a virtual assessment of stability and impingement is performed before drilling the tunnel, the tunnel is drilled under the guidance of the tracker, and finally, the position and status of the tunnel is assessed. We are now proficient in applying the software and coupling it with our surgical technique, and the procedure has gradually reached a very smooth stage where it can be accurately repeated by different surgeons during the procedure. Thus, the advantages of the double-bundle ligament reconstruction navigation procedure are: 1) improved siting and placement of the bone tunnel; 2) accurate assessment of the bone volume; and 3) risk reduction and accurate drilling of the tunnel. On the other hand, the main disadvantage of the ACL reconstruction navigation procedure is the invasive injury caused by placing the tracer on the tibial and femoral side, especially the quadriceps muscle trauma. This must be further refined in order to avoid additional trauma to normal structures while maintaining the same degree of stability. Navigated surgery will pave the way for the further development of standardized ACL surgical guidelines among a broader group of physicians. This would be a useful educational and training tool. Dynamic Assessment of Rotational Stability In consideration of the frequent references in the literature to variable knee rotation, we have developed a biomechanical meter to quantify the rotational characteristics of the knee for clinical examination. The instrument consists of three main components: a foot brace to prevent ankle rotation, a torsiometer to monitor rotational torque, and a kinematic sensor to measure the amplitude of tibial rotation. The accuracy and reliability of the device was verified in human cadaveric experiments, and high correlation was obtained when compared with the gold standard measurement method. Subsequent application of this instrument to human cadavers revealed a significant increase in the difference in rotational laxity between the right and left side in patients with unilateral ACL injuries compared to healthy subjects with lower extremities. To complement the passive clinical testing, we utilized a high-intensity maneuver to test the patient’s dynamic knee rotation qualitatively. Twenty-six patients with unilateral ACL injuries were invited to undergo either single-bundle repair or double-bundle repair surgery. Prior to ACL repair surgery and for an average of ten months postoperatively, subjects performed a jump landing and ninety-degree steering maneuver during instrumental monitoring with optical motion analysis. The results showed a significant increase in tibial rotation on the preoperative damaged side compared to the healthy side, but this returned to normal after the double-bundle repair surgery. The magnitude of tibial rotation did not differ significantly between surgical approaches. Using a high-intensity steering maneuver in the dynamic functional assessment, it was demonstrated that the double-bundle repair procedure was effective in repairing excess tibial rotation, but there was no significant advantage in improving the characterization of knee rotation with the double-bundle repair procedure compared to the single-bundle repair procedure.