A comparison between a retrograde interference screw, suture button, and combined fixation on the tibial side in an all-inside anterior cruciate ligament reconstruction: a biomechanical study in a porcine model.

BACKGROUND Effective soft tissue graft fixation to the tibial tunnel in all-inside anterior cruciate ligament reconstructions has been reported to be a problem and may lead to retrograde pullout at ultimate load testing. HYPOTHESIS A combined retrograde bioabsorbable screw and cortical-cancellous suture button suspension apparatus would gain stiffness from the button and strength from the screw, thus providing for a larger pullout ultimate load, yield load, and stiffness when compared with either fixation alone in an all-inside anterior cruciate ligament reconstruction. STUDY DESIGN Controlled laboratory study. METHODS Eighteen porcine tibias (average bone mineral density of 1.46, measured by dual-energy x-ray absorptiometry scan) and 18 bovine extensor tendon allografts were divided into 3 groups: retrograde bioabsorbable screw fixation, cortical-cancellous suture button suspension apparatus fixation, and combined fixation in the tibia, with 6 specimens per group. They were biomechanically tested with cyclic (500 cycles, 50-250 N, 1 Hz) and load-to-failure (20 mm/min) parameters. RESULTS During cyclic testing, the retrograde screw-only group had a larger cyclic displacement (2.98 +/- 2.28 mm) than the suture button with retrograde screw combination group (1.40 +/- 0.34 mm). The combination fixation group also produced a higher cyclic stiffness (161.93 +/- 61.81 N/mm) than the retrograde screw-only group (91.59 +/- 43.26 N/mm). In load-to-failure testing, the retrograde screw with suture button combination group withstood significantly higher initial failure forces (873.87 +/- 148.74 N) than the retrograde screw-only (558.44 +/- 126.33 N) and suture button-only (121.76 +/- 40.57 N) groups. Additionally, ultimate loads were also significantly higher for the combination group (1027 +/- 157.11 N) than either the retrograde screw group (679.00 +/- 109.44 N) or the suture button group (161.00 +/- 29.27 N). The retrograde screw with suture button combination group showed significantly higher pullout stiffness (152.50 +/- 46.37 N/mm) than either the retrograde screw-only group (78.31 +/- 12.85 N/mm) or the suture button-only group (25.79 +/- 9.30 N/mm). CONCLUSION Soft tissue grafts fixed with a combination of a retrograde screw and a suture button were able to withstand higher initial failure and ultimate failure loads and were also stiffer than grafts fixed with either a retrograde screw or a suture button alone. CLINICAL RELEVANCE These findings may prove useful in providing additional stability when using an all-inside technique in a difficult case, or in a patient with poor bone stock, and may also be useful as an alternative to more commonly used tibial tunnel soft tissue fixation techniques.