Internal brace augmentation in ACL reconstruction increases structural strength and stiffness: a biomechanical study in a porcine model

Abstract This study was to compare the biomechanical outcomes of three ACL graft tibial fixation. Biomechanical testing was performed on 36 fresh porcine tibias and flexor profundus tendon divided into three groups: interference screw group (n = 12), internal brace group (n = 12) and combined group (n = 12). The samples underwent cyclic loading at 1 Hz at 50–250 N for 1000 cycles, following by load-to-failure testing (200mm /min). The cyclic displacement, stiffness and ultimate failure loads were compared between the techniques. No sample failed during cyclic load test. The mean periodic displacement of the combined group(1.97 ± 0.32mm)was significantly lower than both the internal brace group (2.85 ± 0.43mm; p < 0.05) and interference screw group (2.48 ± 0.31 mm; p༜0.05), but there was no significant difference between two fixation alone groups. The mean failure load of combined fixation (821.71 ± 78.39N) was higher than that with interference screw (631.97 ± 109.96N; p < 0.01) or internal brace (566.04 ± 57.68 N; P < 0.01) fixation alone. The combined group showed greater pullout stiffness (217.79 ± 36.66 N/mm) than both the interference screw (151.69 ± 30.28 N/mm; p < 0.01) and internal brace (162.94 ± 35.42 N/mm; p < 0.01) groups. The ultimate failure load and stiffness of soft tissue grafts fixed with internal brace and interference screw were significantly higher than those fixed alone.