A finite element simulation of the effect of graft stiffness and graft tensioning in ACL reconstruction

Background. The anterior cruciate is the most frequent knee ligament to be totally disrupted. Surgical reconstruction of the anterior cruciate ligament is a common practice to treat the disability or chronical instability of knees due to anterior cruciate ligament insufficiency. Some of the factors that influence the success or failure of the anterior cruciate ligament reconstruction are the integrity of secondary restraints, the preoperative laxity of the knee, the status of the articular and meniscal cartilages, the selection of the graft material, the surgical technique, the graft tension and the postoperative rehabilitation. Methods. In this paper we present and discuss the results obtained with a three-dimensional finite element model of the human knee joint corresponding to different aspects of human anterior cruciate ligament reconstruction. In particular, this model was used to investigate the effect of graft stiffness and graft tensioning on the knee joint biomechanics. The initial graft tension was set to 0, 20, 40 or 60 N with the knee at 0°, 30° and 60° of flexion. Three different stiffnesses corresponding to those of patellar tendon, gracilis and quadrupled semitendinosus grafts were analyzed. Findings. The resulting kinematics in each of these cases under an anterior load of 134 N was compared to that of the intact knee. The obtained results showed that, after reconstruction, the closest anterior tibial translation to that of the intact knee is obtained with a bone-patellar tendon-bone graft with a pretension of 60 N. Interpretation. However, this initial tension produces an important additional stress in the graft during the knee movement. This may cause problems in revascularization and remodelling during the postoperative healing process. A lower pretension of about 40 N should therefore be recommended in the present conditions.