RÉSUMÉ
Objective:To establish a three-dimensional model of locking plate fixation for 42A2 type oblique tibial fractures with different fracture line directions and different angles between the fracture line and the long axis of the tibia. Finite element analysis was used to calculate and analyze the biomechanics of locking plate, screw, and tibia, providing theoretical basis for clinical application.Methods:A healthy adult volunteer, 25 years old, male, with a height of 173 cm and a weight of 69.5 kg, was selected to perform computed tomography (CT) scans on the left tibia. Relevant data were obtained to establish a locking steel plate fixation model for 42A2 type tibia with different oblique fracture line directions and different angles between the fracture line and the long axis of the tibia. Eight hole pure titanium plates were used for fixation, respectively. We compared the Mises stress changes of locking plates, screws, and tibia in different angle fracture models.Results:In the case of a 42A2 type fracture in the left oblique direction with a fracture line from outside to inside, the maximum Mises stress in the tibia was 114 MPa, the maximum Mises stress in the screw was 279.8 MPa, and the maximum Mises stress in the locking steel plate was 302.4 MPa; In the case of a 42A2 type fracture in the right oblique fracture with a fracture line from the bottom to the top, the maximum Mises stress of the tibia was 93.41MPa, the maximum Mises stress of the screw was 353.4 MPa, and the maximum Mises stress of the locking steel plate was 411.8 MPa.Conclusions:Regardless of the oblique fractures in both left and right directions, the maximum stress values are: locking plate>screw>tibia; When the position of the locking steel plate is fixed, the maximum stress values of the locking steel plate and screw are both right oblique fracture>left oblique fracture; And the maximum stress values all increase with the increase of angle.
RÉSUMÉ
Objective:To analyze the symmetry of different reference planes in the surgical simulation design of patients with protrusive jaw deformity with high and low eyes.Methods:Fifteen patients with partial jaw deformity were selected from January 2019 to June 2020, including 3 males and 12 females, aged 18-26 years, with average 23.78 years. Inclusion criteria were that the patients, aged more than 18 years, were diagnosed as protrusive jaw deformity with maxillary occlusal plane tilt and high and low eyes by clinical and imaging analysis. Three different 3D reference plane systems were established by different modeling methods. The distance between the landmarks of soft and hard tissues and the median sagittal plane was measured. The symmetry of skull was qualitatively analyzed by mirror image technique. The difference of three reference planes in surgical simulation symmetry of patients with protrusion jaw and high and low eyes was evaluated by one-way ANOVA.Results:Qualitative analysis showed that in the three measurement planes, the symmetry of the third reference plane was the best, and the symmetry of the second and the first was poor. Quantitative analysis showed that in measurement index of hard tissue, there was statistical difference between the distance of each landmark in the reference plane established by Method 3 and Method 1, Method 2 [(1.65±1.19) mm; (3.37±1.58) mm; (3.26±2.36) mm, P<0.05], but there was no statistical difference between Method 1 and Method 2 (P > 0.05). The measurement result of soft tissue was consistent with that of hard tissue, and the distance of each landmark in Method 3 from the median sagittal plane was very small, and the mean error was less than 0.5 mm, which was consistent with the clinical results. Conclusions:Digital model surgery technology can assist orthognathic surgeons in the design and prediction of surgical scheme, especially for patients with special partial jaw deformity.