| Objective:Through the establishment of the "point cloud" database of the proximal tibia,we developed a new anatomical internal fixation system for the treatment of posterior tibial plateau fractures,and compared the stability of the new anatomical plate and other fixation devices in the treatment of posterior tibial plateau fractures through finite element analysis.Methods:1.Screening standard knee joint mode 200 cases of normal adult knee joint thin-layer CT data were collected,100 cases of male and 100 cases of female.The three-dimensional model of knee joint was reconstructed by Mimics software,and the following parameters were measured: posteromedial height of tibial plateau,posteromedial arc length,posteromedial slope arc length,posteromedial slope angle,posteromedial shaft angle,posteromedial anteroposterior diameter of tibial plateau,width of tibial plateau,and width of tibial plateau Posterolateral height,posterolateral arc length,posterolateral slope arc length,posterolateral platform arc,posterolateral slope angle,posterolateral shaft angle,posterolateral anteroposterior diameter.According to the ascending order of the tibial plateau slope angle,the median of each interval of the posteromedial and posterolateral tibial plateau was selected as the reference for the selection of standard knee joints.Two cases of posteromedial and posterolateral standard knee joints were selected and saved in the "point cloud" format.2.Design of new anatomical plate for posterior tibial plateau The selected standard knee joint "point cloud" file was imported into Geomagic studio 2017 software,and saved as STL format file after triangular patch reconstruction,defect repair and fairing,and then imported into imageware13.2 software to design the bottom surface of the plate.We designed the plate into five shapes:(1)posteromedial type: covering the posteromedial tibial plateau,the plate was designed as an "inverted L" type,with the proximal transverse arm supporting the posteromedial tibial plateau,and the distal longitudinal arm fixed on the posteromedial side of the upper tibial segment(2)Medial posterior type: covering the posteromedial and medial tibial plateau,it is designed as "inverted L" type,the proximal transverse arm supports the medial and posteromedial tibial plateau,and the distal longitudinal arm is fixed at the posterior side of the upper tibial segment(3)Medial type: covering the medial tibial plateau,designed as a "t" type,the proximal transverse arm can support the entire medial platform,and the distal longitudinal arm is fixed on the medial side of the upper tibial segment(4)Posterolateral type: it covers the posterolateral tibial plateau and is designed as an oblique "t" type.The proximal transverse arm supports the posterolateral tibial plateau and the distal longitudinal arm is fixed on the posteromedial side of the upper tibial segment(5)Lateral posterior type: it covers the lateral and part of the lateral posterior tibial plateau,and is designed as an inverted "L" type.The proximal transverse arm can support the lateral and part of the posterolateral tibial plateau,and the distal longitudinal arm is fixed on the lateral side of the upper tibial segment.Then,screw holes are added:(1)cross arm: locking hole and pre bending groove are added(2)Longitudinal arm: the epiphysis was added with oval common hole;Sliding hole and8-shaped hole were added in the upper tibia(one locking hole and one common hole in the hole).The direction of screw hole is perpendicular to the plane.3.Finite element analysis of new bone plate and different fixation methods Two standard knee joints(145 ° posteromedial and 135 °posterolateral)were introduced into Geomagic Studio2017 software established NURBS closed surface knee joint model,saved in step file format and imported into Solid Works 2019 software to simulate the manufacture of posterolateral tibial plateau fracture,posteromedial tibial plateau fracture and medial tibial plateau fracture,and constructed new posterolateral tibial plateau anatomical plate fixation model and distal radius oblique T-type plate fixation model,posteromedial anatomical plate fixation model and straight type plate fixation model Then,the assembled fixation model was imported into abaqus6.14 software for grid generation,and the bone plate,screw and proximal tibia were assigned values respectively.The binding connection relationship between the fixator and the bone was set,and the following static analysis was carried out:(1)the lower tibial segment was constrained,and the upper tibial segment was limited Six degrees of freedom were applied to the tibial plateau surface of7 groups of tibial plateau fracture fixation models with 1500 N axial load,(2)the lower tibial segment was constrained to restrict the movement of 6degrees of freedom,and 1500 N axial load was applied to the posterior surface of tibial plateau of 7 groups of tibial plateau fracture fixation models,(3)the lower tibial segment was constrained to restrict the movement of 6 degrees of freedom,respectively 600 N load was applied on the surface of fracture block of posterolateral fracture model of bone plateau,900 N load was applied on the surface of posteromedial fracture block of tibial plateau in two groups,and 900 N load was applied on the surface of medial fracture block of tibial plateau in three groups.The von Mises stress distribution and overall displacement distribution of different fixation methods under three static modes are analyzed.Results:1.The results of anatomical measurement of 200 cases of proximal tibia showed that the posteromedial height of tibial plateau in male and female was(15.88 ± 1.82)mm、(15.50 ± 2.94)mm;The length of posterior medial arc of tibial plateau in male and female was(33.56 6 ± 4.05)mm、(32.06 ± 3.67)mm;The length of posterior medial slope of tibial plateau in male and female was(14.95 1 ± 3.28)mm 、(14.83 ± 2.23)mm;The posteromedial curvature of tibial plateau in male and female was(117.97 0± 4.54)°、(one hundred and eighteen point eight three ± 4.21)°;The posteromedial slope angle of tibial plateau in male and female was(145.911 ± 8.06)°、(one hundred and forty-four point zero one ± 10.18)°;The posteromedial tibial plateau angle of male and female was(146 ± 7.91)°、(one hundred and forty-five point zero three ± 9.52)°。 The posterolateral height of tibial plateau in male and female was(13.86 0 ± 2.06)mm、(13.79± 2.56)mm;The posterolateral arc length of tibial plateau in male and female was(37.71 1 ± 4.41)mm、(38.14 ± 4.28)mm;The arc length of posterolateral tibial plateau in male and female was(15.29 2 ± 4.03)mm、(15.94 ± 4.70)mm;The posterolateral curvature of tibial plateau in male and female was(122.97 0 ± 7.72)°、(one hundred and twenty-three point four one ± 8.49)°;The posterolateral slope angle of tibial plateau was(134.70 0 ± 13.12)° 、(one hundred and thirty-five point four nine ±12.52)°;The posterolateral tibial plateau shaft angle of male and female was(149.80 0 ± 10.82)°、(one hundred and fifty-two point zero two ±10.03)°,There was no significant difference between male and female(P > 0.05).The posteromedial and posterolateral slope angles of the tibial plateau had the largest difference in the posteromedial and posterolateral anatomical parameters of the proximal tibia,respectively.We used this value as the reference for screening the standard knee joint,arranged the measurement results in ascending order,and selected the median of the interval as the reference for selecting the standard knee joint.2.According to the selected standard knee joint,we have designed four types of anatomical bone plates.In Solid Works 2019 software,the bottom surface is thickened,and the equal radius 0.3mm round edge and equal radius 2mm fillet are imported.There are two characteristics of the plate:(1)the thickness of the transverse arm is 1.5mm,the width of the posterolateral anatomical plate is 7mm,the length is 25 mm,three locking holes with a diameter of 2.4mm are added,and pre bending grooves are added on both sides of the joint between the transverse arm and the longitudinal arm.The width of the rear medial plate is 8mm and the length is 32 mm.Three locking holes with a diameter of 2.7mm are added.Pre bending slots are added on both sides of the joint between the transverse arm and the longitudinal arm.The width and length of the posteromedial plate were 8mm and 35 mm respectively.Two 2.7mm locking holes were added at the rear side and three 3.5mm locking holes were added at the inner side.The width and length of the medial plate were 8mm and 60 mm respectively.Three 2.7mm locking holes were added at the back side and four 3.5mm locking holes were added at the inner side.(2)Longitudinal arm: the slope thickness is 1.5mm and gradually thickened to 2mm,and one oval common hole of 3.5mm is added.The width of the rear outer joint plate is 10 mm and the length is 18 mm.One 3.5mm ordinary hole and 23.5mm locking holes are added;The width of the inner plate at the rear is10 mm and the length is 15 mm.One 3.5mm ordinary hole and 4 3.5mm locking holes are added;The width of the back inner plate is 10 mm and the length is 15 mm.One 3.5mm ordinary hole and 5 3.5mm locking holes are added;The width and length of the inner plate are 15 mm.One 3.5mm ordinary hole and 5 3.5mm locking holes are added.The direction of screw holes is perpendicular to the plane.3.We have constructed 7 kinds of finite element models for the fixation of posterior tibial plateau fractures: posterolateral anatomical plate,oblique T-shaped plate for the fixation of posterolateral tibial plateau fractures;posteromedial anatomical plate,straight plate for the fixation of posteromedial tibial plateau fractures;posteromedial anatomical plate,medial anatomical plate,double plate for the fixation of tibial plateau fractures Medial fracture model(1)When the load was applied to the whole tibial plateau,the maximum displacement was 0.082 mm and 0.098 mm respectively;the maximum stress of tibial plateau was 5.96 MPa and 6.79 MPa respectively;the maximum stress of plate was 34.14 MPa and 23.01 MPa respectively;the maximum stress of screw was 54.77 MPa and 55.68 MPa respectively.When the load is applied on the posterior side of tibial plateau,the maximum displacement is 0.142 mm and 0.371 mm respectively;the maximum stress of tibial plateau is 100.40 MPa and 93.63 MPa respectively;the maximum stress of plate is 149.90 MPa and 132.40 MPa respectively;the maximum stress of screw is 513.90 MPa and 572.20 MPa respectively.The maximum displacement was 0.106 mm and 0.424 mm when the load was applied on the posterolateral fracture block;the maximum stress on the tibial plateau was 47.95 MPa and 53.97 MPa respectively;the maximum stress on the plate was 107.20 MPa and 153.30 MPa respectively;the maximum stress on the screw was 287.70 MPa and 383.00 MPa respectively.(2)The model of posteromedial tibial plateau fracture was fixed with posteromedial anatomical plate and straight plate,When the load is applied to the whole tibial plateau,the maximum displacement is 0.303 mm and0.309 mm respectively;the maximum stress of tibial plateau is 9.10 MPa and 9.77 MPa respectively;the maximum stress of plate is 59.35 MPa and81.98 MPa respectively;the maximum stress of screw is 80.94 MPa and95.28 MPa respectively.The maximum displacement was 0.464 mm and0.475 mm respectively when the load was applied on the posterior side of tibial plateau;the maximum stress of tibial plateau was 82.95 MPa and82.98 MPa respectively;the maximum stress of plate was 173.00 MPa and145.00 MPa respectively;the maximum stress of screw was 189.40 MPa and232.00 MPa respectively.The maximum displacement was 0.585 mm and0.745 mm when the load was applied on the posteromedial fracture block;the maximum stress on the tibial plateau was 96.79 MPa and 110.80 MPa respectively;the maximum stress on the plate was 232.60 MPa and240.80 MPa respectively;the maximum stress on the screw was 372.60 MPa and 502.50 MPa respectively.(3)The medial tibial plateau fracture model was fixed with posteromedial anatomical plate,medial anatomical plate and double plates,When the load is applied to the whole tibial plateau,the maximum displacement is 0.343 mm,0.301 mm,0.281;the maximum stress of tibial plateau is 3.77 MPa,3.82 MPa,4.35MPa;the maximum stress of plate is119.70 MPa,84.79 MPa,88.19MPa;the maximum stress of screw is132.00 MPa,91.31 MPa,96.77 MPa.When the load is applied on the posterior side of tibial plateau,the maximum displacement is 0.368 mm,0.317 mm and 0.302 mm respectively;the maximum stress of tibial plateau is 78.89 MPa,78.09 MPa,79.34 MPa respectively;the maximum stress of plate is 140.80 MPa,90.37 MPa and 91.17 MPa respectively;the maximum stress of screw is 136.80 MPa,117.20 MPa and 101.90 MPa respectively.The maximum displacement was 0.215 mm,0.214 mm,0.193 mm when the load was applied on the posteromedial fracture block;the maximum stress on the tibial plateau was 10.57 MPa,10.89 MPa,10.38 MPa;the maximum stress on the plate was 121.20 MPa,91.73 MPa,119.60 MPa;the maximum stress on the screw was 101.50 MPa,92.98 MPa,79.95 MPa.Conclusions:We have successfully developed four new types of posterior tibial plateau anatomical plates to meet the clinical needs.The new anatomic plates of posterolateral and posteromedial tibial plateau have higher strength and better fixation stability.The strength of the new posteromedial and medial tibial plateau anatomic plates is close to the stability of fixation and double plates.It is easy to place and can reduce the operation time. |
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