THE STRESS IN THE ACL, ACL GRAFT, AND OTHER JOINT ELEMENTS WHILE WEIGHT-BEARING IN FULL EXTENSION DEPENDING ON THE...

The safety of early weight bearing after anterior cruciate ligament (ACL) reconstruction and the degree of posterior tibial slope (PTS) impact on ACL and ACL graft are still uncertain due to the limitations of previous studies. The study aimed to evaluate the effect of PTS change on ACL and ACL graft stress. We created the complex multicomponent static models of physiologically normal knee joint, taking into account the different PTS, the ligaments of the knee joint, including the ALL, articular cartilage, and menisci, literature data on muscle tension also with double-bundle ACL and single-bundle ACL graft to determine deformations and stress on the anatomical elements of the joint at a qualitatively new level. Stress in the knee structures was assessed using the finite element method separately with a 6 mm diameter double-bundle normal ACL and an 8 mm single-bundle ACL graft for the two variants of the tibial plateau slope: 5° and 13.9°. Raising PTS from 5° to 13.9° increases stress in the ACL by 1.29 - 1.45 times and in the single-bundle ACL graft by 1.75 - 1.81 times in the upright position with knees in full extension. Stress in ALL increases with higher PTS by 1.58-2.00 times in the knee joint with double-bundle ACL and 1.93-2.02 times in the knee joint with single-bundle ACL graft while weight bearing in full extension. Increasing the PTS angle from 5° to 13.9° with healthy ACL stress in the meniscus increases by 1.05 - 1.34 times, and with a single-bundle ACL graft - by 2.04 - 2.30 times. Replacing the double-bundle ACL with the single-bundle ACL graft also causes an increase in its stress compared to intact ACL under all studied conditions. Increased PTS and ACL reconstruction significantly increase stress in most knee anatomical elements while weight bearing in full extension. Even with a total weight of up to 150 kg, the critical value of stress for the rupture of the ACL graft from a one-time load is not achieved even after reducing its breaking load in 6 weeks. In the early postoperative period, the weakest link is the fixation of the graft with the interference screw. Cyclic load on the fully extended knee (regular walking) can provoke slipping out of the graft from under the interference screw.