ACL reconstruction by bone-patellar tendon-bone graft: mechanical evaluation of the elastic modulus and failure modes

The aim of this study was to apply an engineering approach to study the biomechanical behaviour of both native and reconstructed anterior cruciate ligaments (ACL) under tensile test, simulating the primary stability of the reconstructed ACL in the immediate postoperative period, when the bone callus has not formed yet. We used the bovine bone-patellar tendon-bone grafts to reconstruct ACL in bovine knees. The grafts were fixed by means of titanium interference screws and titanium transverse compressive screws. We tested 18 native and 18 reconstructed ligaments (7 with interference screws and 11 with transverse compressive screws). We applied mechanical tension at a 500 mm/min strain rate, and observed the mode of failure. The data analysis confirmed the different behaviour recorded in load elongation curves, a difference enhanced in stress-strain curves for both fixation methods. The stress-strain patterns for the interference screw and for the native ligament were quite similar.