Subcortical Backup Tibial Fixation in Anterior Cruciate Ligament Reconstruction Has Similar Maximal Strength to Current Techniques

PURPOSE: To evaluate the biomechanical profile of subcortical backup fixation (subcortical button [SB]) in anterior cruciate ligament (ACL) reconstruction as compared with a bicortical post and washer (BP) and suture anchor (SA) when used with interference screw (IS) primary fixation and to evaluate the utility of backup fixation for tibial fixation with extramedullary cortical button primary fixation. METHODS: Fifty composite tibias with polyester webbing–simulated graft were used to test constructs across 10 methods. Specimens were separated into the following groups (n = 5): 9-mm IS only, BP (with and without graft and IS), SB (with and without graft and IS), SA (with and without graft and IS), extramedullary suture button (with and without graft and IS), and extramedullary suture button with BP as backup fixation. Specimens were tested under cyclic loading and then loaded to failure. Maximal load at failure, displacement, and stiffness were compared. RESULTS: Without a graft, the SB and BP had similar maximal loads (802.46 ± 185.18 N vs 785.67 ± 100.96 N, P = .560), and both were stronger than the SA (368.13 ± 77.26 N, P < .001). With graft and an IS, there was no significant difference in maximal load between the BP (1,461.27 ± 173.75 N), SB (1,362.46 ± 80.47 N), and SA (1,334.52 ± 195.80 N). All backup fixation groups were stronger than the control group with IS fixation only (932.91 ± 99.86 N, P < .001). There was no significant difference in outcome measures between the extramedullary suture button groups with and without the BP (failure loads of 721.39 ± 103.32 N and 718.15 ± 108.61 N, respectively). CONCLUSIONS: Subcortical backup fixation in ACL reconstruction has similar biomechanical properties to current methods and is a viable backup fixation alternative. Backup fixation methods work synergistically with IS primary fixation to strengthen the construct. There is no advantage to adding backup fixation to extramedullary button (all-inside) primary fixation when all suture strands are secured to the extramedullary button. CLINICAL RELEVANCE: This study provides evidence that subcortical backup fixation is a viable alternative for surgeons during ACL reconstruction.