| Objective: In transtibial posterior cruciate ligament(PCL)reconstruction,increasing the angle of tibial tunnel relative to the tibial plateau can alleviate "killer turn" effect.However,an excessive angle would lead to a high risk of graft entering the bone marrow cavity,thus affecting the healing of tendon to bone.At the same time,because of the special anatomy of the proximal tibia,an excessive angle would produce the risk of tunnel fracture.Therefore,we proposed the concept of "theoretical optimal angle(TOA)" for the tibial tunnel to take the "killing turn" effect and the healing of tendon to bone into account.In addition,measuring the "permissible maximum angle(PMA)" of the tunnel to prevent fracture of the posterior tibial tunnel wall.In the first and second part of this study,TOA and PMA were evaluated by computed tomography(CT)images of the knee.Besides,there is no consensus for the position of interference screw used in the tibial aperture fixation of the graft.The third part of this study intends to compare the initial fixation strength of three graft fixation methods(distal fixation,proximal fixation,and combined fixation)within the tibial tunnel through biomechanical study.Methods: The contents of the first and second parts were measuring the related parameters on the sagittal plane of the knee CT.The parameters of the first part including TOA of the tibial tunnel during PCL reconstruction,the thickness of cancellous bone(L1)at the proximal tibia,the distance from the tunnel entrance to the anterior edge of the tibial plateau(L2)and the distance from the tunnel entrance to the tibial tuberosity(L3).The parameters of second part including PMA of a 10-mmdiameter tibial tunnel during PCL reconstruction,anterior-posterior diameter(APD)of the tibial plateau,the distance from the center of the PCL attachment point to the posterior edge of the tibial plateau(PPED),and the angle between the tibial plateau and the PCL attachment slope(PSA).The above parameters were measured separately by two researchers according to the established scheme.Finally,intra-observer and intraobserver reliability analyses were performed using intraclass correlation coefficients(ICCs).The results were processed by subgroup analysis.The age subgroup includes the young group(18-30 years),the middle-aged group(31-45 years),and the elderly group(46-60 years).The height sub-group includes group I-~ 1.65 m,group II-1.66 ~ 1.75 m,group III-1.76 m ~.The third part used the bovine extensor tendons and porcine tibias to establish a PCL reconstruction tibial model in vitro.According to the different fixation methods of the graft,specimens were divided into distal fixation(group I,n = 10),proximal fixation(group II,n = 10),and combined fixation(group III,n = 10),load-to-failure tests were conducted by the biomechanical testing machine.The loadelongation curve,tensile stiffness(in newtons per millimeter),ultimate load(in newtons),yield load(in newtons),energy absorbed to failure(in joules),and failure mode were recorded.Results: In total,408 knees were included separately in the first and second sections.The average values of TOA,L1,L2,and L3 in the first part were 35.4 ± 7.9 °,40.1 ± 7.6mm,47.0 ± 11.1mm,and 26.8 ± 11.4 mm,respectively.The average of L1 and L2 was significantly higher in male than those in female(P < 0.05).The average values of L1,TOA,L2,and L3 in the middle-aged group were significantly larger than those in the young group(P < 0.05),and there was no significant difference in parameters between the elderly group and the above two groups(P > 0.05).The average values of L1 and L2 in group I were significantly lower than those in group II and group III(P < 0.05),but there was no difference between group II and group III(P > 0.05).TOA and L3 were not affected by gender and height.ICCs ranged from 0.641 to 0.909.In the second part,the average values of PMA,OTD,APD,PPED,and PSA were 48.2 ± 5.4 °,46.6 ± 4.2 mm,33.2 ± 3.1 mm,18.1 ± 3.0 mm,123.4 ± 5.7 °,respectively.The mean values of OTD,APD,PPED,PSA,and height were significantly higher in male than those in female(P < 0.05).There was no significant difference in the average values of PMA,PPED and PSA between different age groups(P > 0.05),but the average values of OTD,APD,and height in the elderly group were significantly lower than those in the middle-aged group(P < 0.01).The average values of OTD,APD,and PPED increased significantly with height,P < 0.05.Besides,PSA values were significantly greater in group III than those in group I(P = 0.034).The value of PMA was not affected by gender,age,and height(P > 0.05).ICCs ranged from 0.677 to 0.912.In the third part,all graft-screw-tibia complexes failed by the grafts slipping past the interference screws.The average values of the tensile stiffness,yield load,and energy consumption of group I are significantly lower than those of group II and group III(tensile stiffness,19.25 ±.68 N/mm in group I v 34.92 ± 16.48 N/mm in group II [P = 0.016] and 32.31 13.79 N/mm in group III [P = 0.041];yield load,265.36 ± 144.52 N in group I v 398.23 ± 57.04 N in group II [P = 0.006] and 424.94 ± 74.00 N in group III [P = 0.001];and energy absorption,5.16 ± 2.35 J in group I v 19.95 ± 3.48 J in group II [P < 0.001] and 21.09 ± 4.29 J in group III [P < 0.001]).In addition,the results of the analysis of variance showed that there was no significant differences in the ultimate load between the groups(P > 0.05),and no significant differences were found in biomechanical properties between group II and group III(P > 0.05).Conclusion: In transtibial anatomic PCL reconstruction,TOA(35.4 ° ± 7.9 °)and L3(26.8 ± 11.4 mm)could be used as a reference for ideal tibial tunnel(10 mmdiameter)placement,so as to prevent recurrent PCL laxity and ensure good graft healing.However,further clinical validation is needed.PMA of the 10 mm-diameter tibial tunnel relative to the tibial plateau was 48.2°.Compared with distal fixation in transtibial PCL reconstruction,proximal fixation and combined fixation showed superior time-zero biomechanical properties. |
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