| Objectives:To establish a multi-flexion angle three-dimensional finite element analysis models of knee joint,simulate the stress distribution characteristics of ACL in normal adults,determine the ACL direct insertion points,develop a set of 3D printing individualized bone tunnel locator for anterior cruciate ligament(ACL)reconstruction.Explore the early clinical outcome of 3D printing individualized locator assisted ACL anatomical reconstruction.Methods:Multi-flexion angle models(0°、15°、30°、45°、60°、75°、90°、105° and 120°)of knee joint were established based on MRI data of healthy adults’ knee joints,the stress distribution of ACL and its footprint areas at different angles were simulated and analyzed to find the direct insertion points.Three dimensional model of knee joint was established based on CT data of healthy adult knee joint,and individualized locators were designed according to the direct insertion points of ACL.After 3D printed,the simulated operation were performed,and the positions of actual positioning points and designed positioning points were compared and analyzed.A total of 80 patients with ACL rupture from January 2019 to June 2020 in the Department of Sports Medicine,First Affiliated Hospital of Kunming Medical University were selected and randomly divided into conventional group(40 cases)and 3D group(40 cases)by using computer-generated random number table.The conventional group included 21 males and 19females,18 left knees and 22 right knees,with an average age of(28.6±5.4)years.In 3D group,there were 18 males and 22 females,17 left knees and 23 right knees,with an average age of(27.3±6.3)years.Patients in the conventional group were treated with conventional anterior cruciate ligament reconstruction under knee arthroscopy,while patients in the 3D group were treated with 3D printing individualized locator assisted anterior cruciate ligament anatomical(direct insertion points)reconstruction under knee arthroscopy.The time of intraoperative localization,the time of first ambulation after operation and postoperative hospital stay were recorded and compared between the two groups.Lysholm scores and IKDC scores were compared before operation,6 months and 12 months after operation.All the subjects had a 3D CT scan at 1-3 after operation.Based on the CT DICOM data,the three-dimensional models of the affected knees were reconstructed.The preoperative designed and the actual postoperative bone tunnel positions of the 3D group were compared and analyzed,and the actual postoperative bone tunnel positions of the two groups were compared.Via Opti_Knee three-dimensional motion analysis system recorded the maximum step length,minimum step length,stride frequency,and the range of motion(the maximum value minus the minimum value)of 6 degrees of freedom(include flexion-extension angle,varus-valgus angle,internal-external rotation angle,anteroposterior displacement,proximal-distal displacement and internal-external displacement)of the knee joint in the two groups at 3rd,6th and 12th month after operation,and compared with the kinematic data of healthy adults.Results:①Based on the MRI data of healthy adult knee joints,the three-dimensional digital finite element analysis model with multiple flexion angles(0°、15°、30°、45°、60°、75°、90°、105° and 120°)were established to simulate and analyze the stress distribution of ACL and its footprint areas at different angles.And then,according to the mathematical average theory,the specific position of the direct insertion points were obtained by the grid method,femur end:(35.8±2.6)%from the blumensaat line,(26.3±3.1)%from the posterior edge of lateral femoral condyle.And tibia end:(38.8±0.9)%from the anterior edge of tibial plateau,(47.7±1.1)%from the medial edge of tibial plateau.②There were no obvious differences between the actual positioning points and the designed positioning points obtained by 3D printing individualized positioning based on CT data design.③After clinical application,the time of intraoperative localization,the time of first ambulation after operation and postoperative hospital stay of 3D group were all shorter than conventional group(P<0.05).There were no difference in the bone tunnel position between the actual postoperative position and the preoperative design in the 3D group(P>0.05).Compared with the 3D group,the positioning of the femoral tunnel was more inferior and shallower in the conventional group(P<0.05).The position of the tibia tunnel was closer to the posterior and medial edge of the tibial platform in the conventional group compared to the 3D group(P<0.05).All patients’ Lysholm and IKDC scores were improved after surgery(P<0.001).At 3 months after operation,Lysholm score and IKDC score of 3D group were better than those of conventional group(P<0.05),and there was no difference between the two groups at other follow-up time points.④There were no significant difference in minimum step length,varus-valgus angle,proximal-distal displacement,internal-external displacement among 3D group,conventional group and healthy adults at 3,6,12months after operation.At 3 months after operation,the maximum step length,flexion-extension angle in 3D group were not differ to healthy adults,but a bit larger than those in conventional group(P<0.05).At the other follow-up time points,there were no difference in maximum step length and flexion-extension angle between the two groups and healthy adults.At 3 months after operation,the stride frequency,internal-external rotation angle,anteroposterior displacement in 3D group were not differ to healthy adults,but a bit smaller than those in conventional group(P<0.05),there were no difference in stride frequency,internal-external rotation angle,anteroposterior displacement between the two groups and healthy adults at the other follow-up time points.Conclusions:①Three dimensional finite element analysis under multiple flexion angles combined with grid method can accurately quantify the specific spatial position of ACL direct fiber insertion points in femur and tibia.②Based on a more realistic and complete three-dimensional finite element model of the knee joint with multiple flexion angles,the direct fiber insertions obtained and provided a theoretical basis for accurate reconstruction of the anterior cruciate ligament.③It is feasible to design a 3D printing individualized ACL bone tunnel locator by using three-dimensional finite element analysis combined with grid method to determine the location of the ACL direct fiber insertion points,and through the anteromedial portal to locate the femoral tunnel.The locator also had good accuracy.④The 3D printing individualized locator in this study improved the positioning accuracy and shorten the intraoperative positioning time,the time of first ambulation after operation and postoperative hospital stay.The early postoperative clinical outcome is satisfactory.⑤3D printing individualized locator assisted arthroscopic ACL anatomical(direct fiber insertion)reconstruction can obtain more rotation stability at early clinical outcome. |
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