There is no consensus regarding which graft should be tensioned and fixed first in combined anterior (ACL) and posterior (PCL) multiligament reconstruction. Most clinical studies tend to tension and fix the PCL first, however there is no biomechanical evidence to support this. The purpose of this study was to determine which sequence of tensioning and fixation better restores normal knee laxity. The hypothesis was that tensioning and fixing ACL first, better restores knee kinematics.
Fifteen unpaired fresh frozen human cadaveric knees were tested after being prepared by dissecting the soft tissue around the femur and tibia approximately 10 cm from the knee joint line and then mounted into metal cylinders. A 6 degree of freedom robotic testing system was used to test each knee under 89 Newton anterior and posterior tibial loads at full extension (FE), 15°, 30°, 60° and 90° of knee flexion, as well as 7 Nm valgus with 5 Nm internal rotation (simulated pivot shift), (d) 5 Nm external rotation at FE, 15º and 30. The knee states that were evaluated were: (1) intact, (2) ACL and PCL deficient (3) ACL-PCL reconstruction with ACL fixation first, and (4) ACL-PCL reconstruction with PCL fixation first. The 3rd and 4th states were randomized. The ACL graft tensioning and fixation first on tibial side (at 30º of knee flexion) followed by PCL fixation (at 90º of knee flexion) then the order of tensioning was reversed for each knee. Anatomic ACL and PCL reconstruction was performed using a single bundle (9 mm) quadriceps tendon autograft for the anterior cruciate ligament (ACL) graft and a single bundle (9.5 mm) hamstrings autograft for the PCL. Both grafts were tensioned equally at 40 Newton. One-way repeated measures analysis of variance (ANOVA) with Bonferroni correction was used to compare knee kinematics between intact, deficient, ACL fixation first, and PCL fixation first. The p value prior to Bonferroni correction was set at 0.05.
There were no statistically significant differences between both sequences regarding knee kinematics. Both sequences failed to fully restore the intact knee kinematics. ACL first showed no statistically differences for anterior tibial translation (ATT) as compared to the intact state at all tested knee flexion angles, while PCL first showed higher than intact ATT at 90º knee flexion (9.05 ± 3.05 mm vs. 5.87 ± 2.40 mm respectively, p = 0.018). Both sequences failed to restore posterior tibial translation (PTT) back to the intact state at 30º (p = 0.001), 60º (p < 0.001) and 90º (p < 0.001).
The most important finding of this study is that no statistically significant difference was found between both sequences in terms of ATT and PTT. ACL first tensioning and fixation restored intact ATT at all tested knee flexion angles. Neither sequence fully restored PTT to the intact state. This is consistent with clinical studies indicating residual posterior laxity after PCL reconstruction whether in isolation or after multi-ligament knee reconstruction.