| Objective: To analyze and discuss the related factors of postoperative femoral tunnel enlargement in patients with MPFL reconstruction,and to judge the relationship between femoral tunnel Angle change and bone tunnel enlargement.The reason of this connection was analyzed by three-dimensional finite element technique,and an effective method to reduce the expansion of femoral tunnel was explored.Methods: A retrospective study was conducted on patients diagnosed with recurrent patellar dislocation and treated with MPFL reconstruction surgery in the Second Xiangya Hospital of Central South University from January 2018 to January 2021.CT of the affected knee of the patients was reviewed on the third day after surgery.The data of patients within 10 mm of the anatomical stop of the femoral tunnel center were included in the study,and those beyond 10 mm were excluded.Imaging data of patients were retained.Patients were followed up periodically at 1 month,6 months,and 1 year postsurgery,including patient satisfaction,patella extrapolation test,fear test,and redislocation.One year after the operation,CT of the affected knee was reviewed to measure the changes of femoral tunnel Angle and tunnel opening width on postoperative CT.The Angle was measured by axial CT radiography with the connection of the two posterior condyles as reference.The width of the femoral tunnel was measured by axial CT radiography with the distance of the femoral tunnel opening.Meanwhile,Lysholm score,Kujala score and Tegner score were recorded for subjective evaluation of knee function.Finally,36 patients met the requirements,including 13 males and 23 females,with an average age of 20.30 years(16-29 years).The measured femur tunnel Angle was divided into three groups according to 0°-10°,10°-20° and 20°-30°.There were 12 cases in 0°-10° group,including 5males and 7 females,5 cases in left knee and 7 cases in right knee,with an average age of(19.75±2.87)years;There were 12 cases in 10°-20°group,including 3 males and 9 females,7 cases in left knee and 5 cases in right knee,with an average age of(20.92±4.19)years.There were 12 cases in the 20°-30° group,including 5 males and 7 females,9 cases in left knee and 3 cases in right knee,with an average age of(20.17±3.38)years.CT data of a volunteer with normal knee function were collected and stored in DICOM format.A normal knee model was established by Mimics Medical 21.0,Geomagic Wrap 2021,SOLIDWORKS 2021 image reconstruction software,and then based on MPFL anatomical reconstruction method.3D joint models of femoral tunnels with different angles were established by SOLIDWORKS 2021 software.Material attributes and contact relationships were assigned and set for all models by Workbench module of ANSYS 2021 R1 finite element processing software.The loading direction and size of the plants moving down at different bending angles were defined.Finally,the stress relationship between the graft and the tunnel in the models with different femoral tunnel angles was analyzed by finite element calculation and the data were recorded.Results: 1.Lysholm score increased from 55.42±6.26 to 87.94±4.18,Kujala score increased from 47.56±8.30 to 88.69±4.06,And Tegner score increased from 2.917±0.77 to 5.11±0.57 before and one year after surgery.All showed significant statistical difference(p <0.0001).All enrolled patients had varying degrees of femoral tunnel enlargement at 1-year follow-up.In the 0°-10° group,10°-20° group,and 20°-30° group,the average distance of femoral tunnel expansion was 0.38±0.09 mm,0.95±0.23 mm,and 1.38±0.37 mm.During the same follow-up period,the distance of femoral tunnel expansion was proportional to the femoral tunnel anteriorness.There was significant statistical difference(p<0.0001,p <0.05).2.Finite element models with different forward angles of femur tunnel produce different equivalent stresses on bone tunnel under different bending states.The maximum equivalent stresses of femur tunnel at 0°,10°,20° and 30° are 17.80 MPa,18.54 MPa,23.67 MPa and 26.08 MPa,respectively.The peak pressure increases with the increase of femur tunnel Angle.The peak pressure increases gently from0° to 10°,while the stress increases obviously from 10° to 20°.The equivalent stress of the femur tunnel under different bending states is inhomogeneous and mainly concentrated in the first half of the tunnel opening.Conclusions: 1.Various degrees of femoral tunnel enlargement were found in the POSTOPERATIVE CT follow-up data of all patients,but no significant correlation was found with the subjective postoperative score in the current follow-up study.2.We suggest that the femoral tunnel rake Angle should be controlled within the range of 0°-10° and the maximum Angle should not exceed 10° during MPFL reconstruction. |
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