Background: There has been concern regarding the fixation of anterior cruciate ligament reconstruction, with soft tissue grafts being strong and stiff enough to allow for early accelerated postoperative rehabilitation. Therefore, some have recommended supplementary fixation for soft tissue tibia interference screw fixation with a staple, to improve the strength and stiffness of the fixation. Unfortunately, with staple supplementation, there is a risk for symptomatic hardware, which may require a second surgery to remove the staple.
Hypothesis: Supplementary fixation with a bioabsorbable knotless suture anchor will improve the structural properties of soft tissue tibia bioabsorbable interference screw (BIS) fixation and be comparable with supplementary fixation with a staple.
Study Design: Controlled laboratory study.
Method: Fifteen porcine tibias and flexor profundus tendons were randomized into 3 fixation study groups: group 1, BIS; group 2, BIS + staple; and group 3, BIS + push-lock screw. The structural properties of the 3 fixation groups were tested under displacement-controlled cyclic loading and load to failure.
Results: No significant difference in mean stiffness (N/mm ± SEM) under cyclic loading was found for BIS (335.31 ± 15.43), BIS + staple (344.81 ± 44.97), and BIS + push-lock (353.28 ± 38.93). Under load-to-failure testing, there were no differences found in stiffness, yield load, displacement at yield load, displacement at ultimate load, and energy absorbed among the 3 fixation methods. BIS + push-lock fixation had a significantly higher ultimate load than BIS alone and BIS + staple (917.85 ± 58.30 N vs 479.83 ± 66.04 N, P = .0003 vs 618.89 ± 8.94 N, P = .004).
Conclusion: Supplementary fixation with staple or push-lock screw did not significantly increase the structural strength and stiffness of the BIS soft tissue graft fixation under cyclic loading, but it did show improvement under load-to-failure testing for ultimate tensile load.
Clinical Relevance: The indication for supplementary fixation for tibial BIS soft tissue graft fixation depends on the fixation that the BIS achieves at the time of the surgery because the tensile load is transferred to the secondary fixation if and only when there is slippage of graft at the primary fixation. The supplementary fixation may be of value in those cases with poor bone quality, such as revision surgery with tunnel widening and/or graft-tunnel mismatch, or possibly in cases with older patients or patients with disorders affecting bone mineral density.