A Comparison of the Fixation Strengths Provided by Different Intraosseous Tendon Lengths during Anterior Cruciate Ligament Reconstruction: A Biomechanical Study in a Porcine Tibial Model

BACKGROUND: The purpose of this study was to determine the tibial fixation strength provided by different intraosseous soft tissue graft lengths within the tibial tunnel. METHODS: Porcine tibial bones and digital flexor tendons were used for testing. Bone mineral densities of proximal tibial medial condyles were measured, and two-strand tendon bundles of 8 mm diameter were used. An intraosseous graft length of 2 cm was used in group 1 (n = 10), and a graft length of 4 cm was used in group 2 (n = 10). Tunnels were 4 cm in length and 8 mm in diameter. Tibial fixation was performed using a suture tied around a screw post with a washer and an additionally inserted 7 × 20 mm bioabsorbable screw. After applying preconditioning loading of 10 cycles, 1,000 cycles between 70-220 N were applied at a frequency of 1 Hz. Graft slippage and total graft movement were recorded. Ultimate tensile strength was measured by pull-out testing at an Instron crosshead speed of 1,000 mm/min. RESULTS: No significant intergroup difference was found for total graft movement after cyclic loading (slippage in group 1, 1.2 mm and group 2, 1.2 mm, respectively, p = 0.917; and total graft movement in group 1, 3.3 mm and group 2, 2.7 mm, respectively, p = 0.199). However, mean ultimate tensile strength in group 2 was significantly higher than that in group 1 (group 1, 649.9 N; group 2, 938 N; p = 0.008). CONCLUSIONS: In a porcine model, ultimate tensile strength was greater for a 4 cm long intraosseous flexor tendon in the tibial tunnel. However, no intergroup difference in graft slippage or total graft movement was observed. The results show that a 2 cm intraosseous graft length in the tibial tunnel is safe and has sufficient strength (> 450 N) for adequate rehabilitation after anterior cruciate ligament reconstruction.