The tibial tunnel drilling angles of 60 degrees provided a lower ultimate load to failure on a single bundle posterior cruciate ligament graft using interference screw fixation compared to 30 degrees/45 degrees

PurposeTo biomechanically compare the initial fixation strength of grafts among three tibial tunnel angles (30 degrees/45 degrees/60 degrees) in transtibial posterior cruciate ligament (PCL) reconstruction.MethodsA series of transtibial PCL reconstruction models were established with porcine tibias and bovine tendons. Specimens were randomly assigned to three groups according to the angles between the tibial tunnel and the perpendicular line of the tibial shaft: Group A (30 degrees, n = 12), Group B (45 degrees, n = 12), and Group C (60 degrees, n = 12). The area of the tunnel entrance, the segmental bone mineral density (sBMD) of the graft fixation site of the tibia and the maximum insertion torque of the interference screw were measured. Finally, load to failure tests were carried out on the graft-screw-tibia constructs at the same rate.ResultsUltimate load to failure in Group C (335.2 +/- 107.5 N) was significantly lower than that in Group A (584.1 +/- 127.9 N, P < 0.01) and Group B (521.9 +/- 95.9 N, P < 0.01). There were no significant differences between biomechanical properties of Groups A and B (n.s.). The posterior part fractures of the tibial tunnel exit occurred in eight specimens of Group C. In addition, the ultimate load was proven to be related to insertion torque (rho = 0.7, P < 0.01), sBMD (rho = 0.7, P < 0.01), and the area of the tunnel entrance (rho =- 0.4, P = 0.01).ConclusionThe ultimate load to failure was significantly lower in tibial PCL interference screw fixation for tunnels drilled at 60 degrees compared to 30 degrees/45 degrees. In addition, the ultimate load was significantly correlated with insertion torque, sBMD and the area of the tunnel entrance. Given that the load to failure of distal fixation may not be sufficient for early postoperative rehabilitation, a 60 degrees tunnel should not be recommended to drill in tibia during PCL reconstruction.