A novel protection liner to improve graft-tunnel interaction following anterior cruciate ligament reconstruction: a finite element analysis

BACKGROUND: Deteriorated bone-graft interaction at the tunnel entrance following ACL reconstruction (ACLR) is considered one of the primary causes of long-term tunnel enlargement and graft wear. Methods have been introduced to improve the long-term outcome, such as novel graft materials or alternative fixation methods, but have been met with varying degrees of success. This study aims to design a protection liner to improve the bone-graft interaction at the tunnel entrances. METHODS: A finite element model of a human cadaveric knee was used to simulate traditional ACLR and ACLR using the protection liner. Stress distribution around the tunnel entrances and on the ACL graft were calculated under a combined loading of 103 N anterior tibial load, 7.5 Nm internal tibial moment, and 6.9 Nm valgus tibial moment at a joint flexion angle of 20°. Results were compared between the traditional ACLR and ACLR using a double liner (femoral and tibial) setup, as well as between the ACLR using a double liner setup and a single liner (femoral side) setup. Different materials (PEEK, Ti-6Al-4V, CoCrMo) for the liner were also evaluated. RESULTS: The traditional ACLR resulted in concentrated stress on the graft where it contacted the tunnel entrance. Correspondingly, there were stress concentrations at the distal posterior zone of the femoral tunnel entrance and medial posterior zone of the tibial tunnel entrance, while the other zones suffered from a stress reduction. Use of the protection liner reduced the stress concentration around the tunnel entrances by up to 89% and increased the stress at the unloaded zones by up to 106%. Also, stress concentration on the graft was slightly decreased (15.4 vs 15.1 MPa) after using the liner. The single liner setup increased the stress concentration around the tibial tunnel entrance. Stiffer materials improved the stress distribution around tunnel entrances but had little effect on the stress on the graft. CONCLUSIONS: The novel protection liner can improve the stress distribution on the graft and at the tunnel entrances, which may be beneficial for improving the clinical outcome of ACLR.