Influence of the diameters of tendon graft and bone tunnel in hamstring ACL reconstruction. A bovine model

In an animal model of Anterior Cruciate Ligament reconstruction by hamstring tendons and 8mm diameter biodegradable interference screws, we aimed to investigate whether pull out forces and failure modes were influenced by changing tendon and bone tunnel diameters. Three groups of 10 calf tibiae each were prepared with 8, 9 and 10mm diameter proximal tunnels fitted respectively with 8, 9 and 10mm diameter tendon grafts. Mean +/- SD pull out force was 607.9 +/- 191.5N in the 8mm group, 494.2 +/- 206.2N in the 9mm group and 530.4 +/- 212.5N in the 10mm group. These differences were not significant at t-test. 8mm specimens failed by tendon rupture, 10mm specimens failed by screw pull out and 9mm specimens failed in both ways. In this ACL reconstruction model, safe pull out forces were achieved by fixing tendon grafts to bone by 8 mm absorbable interference screws regardless of tendon and bone tunnel diameter.