| Background: Posterior cruciate ligament（PCL）reconstruction had a high postoperative failure rate.A number of studies reported that the “killer turn” effect was one of the main reasons for the failure of PCL grafts.However,there is no consensus on the optimal position of the PCL tibial tunnel to minimize the “killer turn” effect.To reduce tendon laceration caused by the “killer turn” effect,surgeons usually performed PCL reconstruction using the maximum angle of tibial tunnel.However,few studies reported the parameters regarding the maximum and safe angle of PCL tibial tunnel based on CT,X-ray and 3D knee models.In this study,based on two-dimensional images（CT and virtual X-ray）and three-dimensional surgical simulation techniques,the maximum and safe angle,tunnel length and tunnel height of the PCL tibial tunnel were measured.In addition,we also explored the formation mechanism of the “killer turn” effect and investigated the biomechanical properties of different tibial tunnels,in order to provide theoretical supports to determine the optimal tibial tunnel position during PCL reconstruction.Objective: 1.In this study,the technique of two-dimensional（CT and virtual Xray）PCL surgical simulation were developed to evaluate the maximum safe angle,the length and height of PCL tibial tunnel.2.The PCL surgical simulation technique was established based on the three-dimensional model of knee joint,and relevant parameters of anterolateral and anterolateral tibial tunnels were measured.We also compared the differences of parameters of PCL tibial tunnels in the two-dimensional and threedimensional states.3.Based on a new hypothesis of the “killer turn” mechanism proposed by us,we quantitatively analyzed the effect of different tibial tunnel positions on the coronal and 3D “killer turn” angles.4.we conducted an in-vitro biomechanical study to investigate the influence of different tibial tunnel positions on the initial fixation strength of PCL tibial-bone complex,in order to provide theoretical supports for the selection of the optimal tibial tunnel position during PCL reconstruction.Methods: 1.The Mimics software was used to simulate the PCL tibial tunnel on2 D CT and virtual X-ray images;and we adjusted the tibial tunnel to the position of the maximum safe angle,and measured the following parameters: the maximum safe angle,tunnel length and tunnel height.2.The anterolateral and anterolateral tibial tunnels were simulated based on the 3D knee models;and the positions of the tibial tunnels were adjusted and the parameters of the tibial tunnel were measured.3.The Rhinoceros software was used to simulate PCL reconstruction,and 2D coronal and 3D “killing turn”angles were quantitatively analyzed based on the same sagittal plane angle（50°）of the tibial tunnel.4.An in-vitro PCL biomechanical model was established,and the initial fixation strength between anteromedial and anterolateral tibial tunnels was compared using a single load-to-failure test.All the above results were statistically analyzed using SPSS software.Results:1.The PCL tibial tunnel was successfully simulated on 2D CT and virtual X ray images.The results based on 2D knee CT images showed that the maximum angle of the PCL tibial tunnel was 49.3° ± 5.4°,the length of the tunnel was 66.1 ± 9.6mm,and the height of the tunnel was 61.8 ± 9.3mm.The results based on virtual X-ray images showed that the maximum angle of the PCL tibial tunnel was 68.4° ± 6.3°,the length of the tunnel was 86.5 ± 9.8 mm,and the height of the tunnel was 80.0 ± 10.7 mm.2.The results showed that the maximum angle in anteromedial tibial tunnel was58.2 ± 8.0°,tunnel length was 67.0 ± 8.9 mm,and tunnel height was 60.5 ± 8.9 mm.The results showed that the maximum angle in anterolateral tibial tunnel was 50.4 ±7.7°,the tunnel length was 59.9 ± 8.4 mm,and the tunnel height was 51.0 ± 9.9 mm.Pearson correlation analysis showed that the tunnel length（anteromedial tunnel: r =0.39,p < 0.001;anterolateral tunnel: r = 0.31,p < 0.001）and tunnel height（anteromedial tunnel: r = 0.34,p<0.001;anterolateral tunnel: r = 0.37,p<0.001）was moderately related with patient height.Subgroup analysis showed that gender had significant influence on tunnel length and tunnel height3.Using the Rhinoceros software,we successfully established the 3D surgical simulation technique of PCL tibial tunnel on 3D knee joint models.The results showed that the coronal angles of anteromedial,tibial tuberosity and anterolateral tunnels were as follows: 127.64°±8.72°,146.24°±6.21°,169.95°±7.43°;the 3D killer turn angle of anteromedial,tibial tuberosity and anterolateral tunnel was 96.76°±7.52°,103.70°±7.51°and 111.62°±7.83°,respectively,and the differences among the three groups were statistically significant（p < 0.05）.As shown in the linear correlation analysis,the correlation coefficient between coronal 2D and 3D killer turn angle is 0.659,indicating that there is a strong correlation between these two parameters.The linear relationship is as follows: y=52.67+0.35*x,x: 2D coronal killer turn angle,and y: 3D killer turn angle).4.The biomechanical test showed that the maximum and yield load of anteromedial tunnel group were significantly higher than those of anterolateral tunnel（maximum load: 499.33 ± 49.90 N vs 396.89 ± 78.76 N,p = 0.003;yield load: 375.03± 62.59 N vs 293.18 ± 60.58 N,p = 0.008）.Conclusions: 1.We successfully developed the techniques of virtual X-ray imaging and PCL 3D surgical simulation based on the Mimics software and Rhinoceros software.These techniques have great clinical values,which can be widely used in preoperative design and related scientific research of PCL reconstruction.2.The average maximum angle of the PCL tibial tunnel was 49° measured on CT images,and 68° on virtual X-ray images.There were significant differences on tunnel parameters between CT and X-ray images.Therefore,we do not recommend to use 2D images（CT and X ray）for preoperative or intraoperative assessment of the position of the PCL tibial tunnel.3.Based on the measurement outcomes of 3D knee models,the mean maximum angle in PCL reconstruction was 58° for the anteromedial tibial tunnel,and was 50° for the anterolateral tibial tunnel.We firstly proposed for the concept of "3-60" for the anteromedial tibial tunnel and "3-50" for the anterolateral tibial tunnel,which were more memorable and practical for surgeons.4.We have preliminary confirmed our hypothesis: the angles of PCL graft and tibial tunnel in coronal and sagittal planes were the key factors of killer turn effect.Therefore,surgeons should not ignore the killer turn formed in the coronal plane,and we should focus on both the coronal and sagittal the killer turn angles to minimize graft laceration.5.Surgeons majoring in sports medicine need to be aware of the “advantages” and“disadvantages” of PCL anterolateral tibial tunnel: anterolateral tibial tunnel theoretically reduced graft laceration,but our biomechanical study showed that the anterolateral tibial tunnel significantly reduced the initial fixation strength of the graft. |
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