The Effect Of Tibial Tunnel Location On Killer Turn Angle And Tunnel Length During Posterior Cruciate Ligament Reconstruction

Objective:When performing the posterior cruciate ligament(PCL)reconstruction,the shear compressive force commonly concentrated on the graft bending places where commonly occurs graft abrasion,elongation and thinning.The"killer turn"effect produced by the graft bending place on the tibial side is one of the important reasons leading to graft failure.In clinical practice,the tibial tunnel location is always adjusted to reduce the killer turn effect.This study aims to(1)establish a method for measuring three dimensional(3D)killer turn angle based on the in-vitro computer 3D knee joint model;(2)determine whether the increase of tibial tunnel angle increases the 3D killer turn angle during PCL reconstruction;(3)explore the influence of tibial tunnel position on graft turning angle in coronal plane,sagittal plane and 3D killing angle when the position of tibial tunnel changes in sagittal plane and coronal plane;(4)provide a method for predicting the 3D killer turn angle;(5)comprehensively consider the influence of the 3D killer turn angle and the tibial tunnel length on the killer turn effect,and discuss the best placement of the tibial tunnel to reduce the killer turn effect;provide a method for predicting the tibial tunnel length before preparing the tibial tunnel.Methods:The method used in the first part were as follows:(1)the 3D knee model was reconstructed by using the Mimics software on the basis of CT images;(2)the 3D knee model was imported into the Rhinoceros software,and the tibial and femoral PCL attachment were marked on the 3D knee model;(3)based on the changes of tibial tunnel in sagittal plane and coronal plane,different tibial tunnels were simulated,and the effect of tibial tunnel angle on the 3D killer turn angle was analyzed;(4)the effects of the graft bending angle in sagittal plane(GASP)and in coronal plane(GACP)on the 3D killer turn angle were quantitatively analyzed.The methods used in the second part were as follows:(1)The PCL attachment point on the femur and tibia were determined by the same method as in the first part;(2)the tibial tunnel entrance points were respectively placed at 2cm posterolateral and posteromedial from tibial crest,and the angle between the tibial tunnel and the tibial plateau were 40°,45°,50°,55°and 60°,respectively;(3)the 3D killer turn angle,length and height of different tibial tunnels were measured by using the measurement function of Rhinoceros software.Linear regression analysis was used to explore the effect of tibial tunnel angle on 3D killer turn angle and tibial tunnel length.Results:The first part of the study included the knee joint CT images of 60 patients.In this study,the anatomical structure of the knee joint was well restored by using Mimics software,and the measurement model of 3D killer turn angle was successfully established by using the Rhinoceros software.The angle between the tibial tunnel and the graft in knee joint in sagittal plane,coronal plane and 3D space were successful measured.The 3D killer turn angle showed a significant proportional relationship not only with the GASP(r~2>0.868,p<0.001),but also with the GACP(r~2>0.467,p<0.001).Every 10°change of the GACP caused 2.8°to 4.4°change of the 3D killer turn angle,whereas every 10°change of the GASP caused 6.4°to 9.2°change of the 3D killer turn angle.The second part of the study included the knee joint CT images of 63patients.The 3D killer turn angle in anterolateral approach with a 50°tibial tunnel angle was significantly greater than it in anteromedial approach with a 60°tibial tunnel angle(p<0.001).There was no difference of the 3D killer turn angle between the anterolateral approach with a 40°tibial tunnel and the anteromedial approach with a 60°tibial tunnel angle(p>0.05).The 3D killer turn angle showed a strong correlation with tibial tunnel angle(for anteromedial approach:r=0.759,p<0.001;for anterolateral approach:r=0.702,p<0.001).Every 10°increase of the tibial tunnel angle caused the3D killer turn angle increase about 8.9°for anteromedial approach(r~2=0.576),and 7.8°for anterolateral approach(r~2=0.493).In anteromedial and anterolateral tibial tunnel approaches,the tibial tunnel length showed a strong correlation with the tibial tunnel angle(for anteromedial:r=0.758,p<0.001;for anterolateral:r=0.727,p<0.001).The best fit equation to calculate the tibial tunnel length based on the tibial tunnel angle was Y=1.04*X+14.96 for males in anteromedial approach,Y=0.93*X+17.76 for males in anterolateral approach,Y=0.92*X+14.4 for females in anteromedial approach,and Y=0.94*X+10.5 for females in anterolateral approach.Conclusion:1.In this study,it is found that with the increase of tibial tunnel angle,the 3D killer turn angle will also increase.In PCL reconstruction,we should consider the effect of the GASP and GACP on the 3D killer turn angle at the same time to maximize the 3D killer turn angle.2.No matter how the tibial tunnel angle is changed in the anteromedial approach,using anterolateral approach is likely to reduce the killer turn effect more effectively than using anteromedial approach.Maximizing the angle of the tibial tunnel in the anterolateral tibia can maximize the 3D killer turn angle.Future studies should explore the 3D killer turn angle and the tibial tunnel length which has more influence on the killer turn effect,so as to determine the best placement mode of tibial tunnel.3.This study provides the best fit equation for predicting the tibial tunnel length based on the tibial tunnel angle for anterior medial and anterolateral approaches of different genders.When preparing the tibial tunnel,predicting the tibial tunnel length could help to avoid the drill bit over-penetrated into the popliteal space to damage the neurovascular structure.