Deterioration of stress distribution due to tunnel creation in single-bundle and double-bundle anterior cruciate ligament reconstructions

Bone tunnel enlargement is a common effect associated with knee laxity after anterior cruciate ligament (ACL) reconstruction. Nevertheless, its exact pathomechanism remains controversial. One of the possible reasons could be bone remodeling due to tunnel creation, which changes the stress environment in the joint. The present study aims to characterize the deteriorated stress distribution on the articular surface, which is due to tunnel creation after single-bundle or double-bundle ACL reconstruction. The stress distributions in the knee following ACL reconstruction under the compression, rotation, and valgus torques were calculated using a validated three-dimensional finite element (FE) model. The results indicate that, (a) under compression, von Mises stress is decreased at lateral and posteromedial regions of single/anteromedial (AM) tunnel, whereas it is increased at anterior region of single/AM tunnel in tibial subchondral bone; (b) the concentration of tensile stress is transferred from the articular surface to the location of graft fixation, and tensile stress in subchondral plate is decreased after ACL reconstruction; (c) severe stress concentration occurs between AM and posterolateral tunnels following the double-bundle reconstruction, which may contribute to the tunnel communication after surgery. In summary, the present study affirms that the deterioration of stress distribution occurs near the articular surface, which may cause the collapse of the tunnel wall, and lead to tunnel enlargement. The present study provides an insight into the effect of tunnel creation on articular stress deterioration after single-bundle or double-bundle ACL reconstruction. These findings provide knowledge on the effect of tunnel enlargement after ACL reconstruction in the long term.