gms | German Medical Science

Introduction: Several biomechanical in vitro studies have suggested that an anatomical ACL reconstruction restoring the anteromedial (AM) and posterolateral (PL) bundle restore the intact knee kinematics more closely. On the other side, authors have expressed their concerns about the stability of the lateral femoral condyle with two tunnels drilled for the reconstruction (Harner and Poehling 2004). Aim of the current study was to evaluate the impact of two different distances (widths) of the bony bridge between the femoral AM and femoral PL bundle tunnel on the stability of the graft/femur complex under cyclic loading in anatomical ACL reconstruction. We hypothesize that a 1 mm bridge may result in inferior mechanical properties when compared to a 2mm bridge.

Methods: Anatomical ACL reconstruction was performed in 20 fresh frozen porcine femora with a resulting bridge of 1 mm (group 1) and 2 mm (group 2) between the AM and PL bundle tunnel. To standardize the bridge width between the 6 mm tunnels for AM and PL bundle, a custom made aimer was used and the graft were fixed using an Endobutton technique. Specimens were mounted in a material testing machine (Lloyd 5k-plus, Great Britain) and the load application was in 90° direction to the AM bundle tunnel. After 1000 cycles of cyclic loading between 50 and 250 N the specimens were loaded to failure at a cross head speed of 200 mm/min. Elongation after 10, 100, 200, 300, 400, 500, 600, 700, 800, 900, and 1000 cycles of load, stiffness, yield load, ultimate failure load, and mode of failure were recorded. Data were analyzed using a Students T-test with the level of significance set at p<0.05.

Results: None of the anatomical ACL reconstructions of group 1 (1 mm) or group 2 (2 mm) failed prior to 1000 cycles of load between 50 and 250 N. After 1000 cycles, all specimens of group 1 (1 mm) showed macroscopic tunnel-widening at the tunnel entrance and 40% showed a fractured bony bridge, whereas none of the specimens of group 2 (2 mm) showed any signs of widening or fracture. No statistical significant differences in load to failure between the two groups was to be found (p>0.05).

Conclusion: A fracture of the bony bridge between the AM and the PL bundle tunnel may distort the healing of the graft/bone interface. Aim of the current study was to evaluate the influence of two different clinical relevant widths of the bony bridge between the femoral AM and femoral PL bundle tunnel on the stability of the graft/femur complex. The results suggest that the indication for anatomical ACL reconstruction may include the size of the lateral femoral condyle. In small knees, a second femoral tunnel may be difficult to locate with a minimum bridge of 2 mm.