Effect of tibial drill-guide angle on the mechanical environment at bone tunnel aperture after anatomic single-bundle anterior cruciate ligament reconstruction

Purpose: The tibial drill-guide angle in anterior cruciate ligament (ACL) reconstruction influences the tunnel placement and graft-tunnel force, and is potentially associated with post-operative tunnel widening. This study aimed to examine the effect of the drill-guide angle on the stress redistribution at the tibial tunnel aperture after anatomic single-bundle ACL reconstruction. Methods: A validated finite element model of human knee joint was used. The tibial tunnel with drill-guide angle ranging from 30° to 75° was investigated. The post-operative stress redistribution in tibia under the compressive, valgus, rotational and complex loadings was analysed. Results: Compressive loading played a leading role on the stress redistribution at intra-articular tibial tunnel aperture. After ACL reconstruction, stress concentration occurred in the anterior and posterior regions of tunnel aperture while stress reduction occurred in the lateral and posteromedial regions under the compressive loading. Stress redistribution was partially alleviated by using the drill-guide angle ranging from 55° to 65°. Conclusions: The present study quantified the effect of bone tunnel drill-guide angle on the post-operative stress redistribution. This phenomenon potentially contributed to tunnel widening. A tunnel drill-guide angle ranging from 55° to 65° was proposed based on the biomechanical rationale. It could serve as a helpful surgical guide for ACL reconstruction.