Finite element analysis of the stability of Mason type Ⅲ radial head fracture fixed with three cross-bridge headless compression screw and locking plate / 中国骨伤

OBJECTIVE@#To compare the biomechanical stability of three cross-bridge headless compression screws and locking plates in the fixation of Mason type Ⅲ radial head fractures by finite element method.@*METHODS@#Using reverse modeling technology, the radial CT data and internal fixation data of a healthy 25-year-old male were imported into the relevant software. Three-dimensional finite element model of 3 cross-bridge headless compression screws and locking plates for MasonⅢ radial head fractures were established, and the radial head was loaded with 100 N axial loading. The maximum displacement, maximum Von Mises stress and stress distribution of the two groups were compared.@*RESULTS@#The maximum displacements of the three cross-bridge screws group and locking plate group were 0.069 mm and 0.087 mm respectively, and the Von Mises stress peaks were 18.59 MPa and 31.85 MPa respectively. The stress distribution of the three screws group was more uniform.@*CONCLUSION@#Both internal fixation methods can provide good fixation effect. CoMPared with the locking plate fixation method, the 3 cross-bridge headless compression screws fixation is more stable and the stress distribution is more uniform.

Finite element analysis of the influence of anchorage number and location on Bankart repair strength of shoulder joint / 中国骨伤

OBJECTIVE@#To study the influence of the number and position of anchor nails on the Bankart repair by the finite element analysis.@*METHODS@#The 3D CT data of shoulder joints including normal adult volunteers were imported into Mimics 10.0 and Geomagic 2012 software to reconstruct the related tissues, and then meshed in Hypermesh 13.0 software to give material attributes. The position and number of MPC constraints were adjusted in Abaqus 6.14 to establish finite element model of shoulder joint under 6 working conditions including A model(normal control model), B model (Bankart damage control model), C model (1 anchor), D model (2 anchors), E model (3 anchors), F model (4 anchors). The humerus external rotation and forward load were added to simulate the fear test of the shoulder joint forward instability.@*RESULTS@#(1)Normally, the inferior glenohumeral ligament complex accompanied by the external rotation of the humerus head has a wrinkle and a significant stress concentration around its anterior and posterior bundle terminations.(2)The stress of the anterior bundle and posterior bundle of the inferior glenohumeral ligament were increased by 52.33% and 45.67% respectively after Bankart's injury.(3)In each model of anchor repair, the stress concentration was obvious at the anchor site, and the stress of anterior and posterior bundle ligaments could be reduced; there were no obvious differences between C, D models and B model(>0.05), and there were significant differences between E, F models and B model(<0.05).@*CONCLUSIONS@#One or two anchors can reduce the stress of the anterior and posterior bundles of the inferior glenohumeral ligament in the repair of Bankart's injury, but when the angle of rotation is large, the stress concentration in the anchor position increases significantly, leading to the increases of the risk of failure. The application of three or four anchors can enhance the constraints on the inferior glenohumeral ligament and reduce the stress of the anchor itself through the "load sharing" effect between anchors, so as to ensure the stability of the shoulder joint and provide a mechanical environment for the early rehabilitation of patients.

Finite element analysis on the effect of lateral wedge insole intervention on the contact characteristics of the subtalar joint / 中国骨伤

<p><b>OBJECTIVE</b>To establish a three-dimensional finite element model of the lower limb bones, and investigate the changes of the contact characteristics of the subtalar joint after using laterally wedge insole intervention.</p><p><b>METHODS</b>Using the reverse modeling technology, the lower limb bones of normal adult volunteers was scanned by CT. Mimics 10.0 and Geomagic Studio 6.0 software were used to reconstruct the 3D morphology of bones and external soft tissue of the feet. The laterally wedge insole was designed in ProE 5.0. And then all the models were imported into Hyperwork 10.0 and meshed, and given the material properties. The finite element analysis was carried out in ABAQUS 6.9.</p><p><b>RESULTS</b>A three-dimensional finite element model of the lower extremity was established, which was consisted of 95 365 nodes and 246 238 elements. The contact area of the standing state of the lower joint was larger than that of the anterior middle joint surface. The peak stress was concentrated in the anterior lateral part of the posterior articular surface, and the average stress value was(3.85±1.03) MPa. Compared with the model of 0°, the contact area of the subtalar joint was reduced accordingly. There was a significant correlation between anterior middle joint ||=0.964,=0.008, and posterior articular ||=0.978,=0.002. The equivalent stress of 0° model distributed from(3.07±1.14) MPa to(3.85± 1.03) MPa, which had no statistically difference. Compared with the 0° model, the equivalent stress of the anterior and middle joint surfaces of the 8° model was significantly reduced(<0.05), but the peak stress of the posterior articular surface was significantly increased(<0.05). In the 12° model, the peak stress was sharply increased to(10.51±3.53) MPa. Compared with 8° model, there was no statistically difference(<0.05). Although the peak stress was slightly increased in 16° model, but compared with 12° model, there was no statistically differences(>0.05).</p><p><b>CONCLUSIONS</b>Although a certain valgus can be obtained in subtalar by wearing LWI, the result comes at the cost of the stress concentration on posterior surface. Through this study, we can find that LWI with 8° tilt angle could provide appropriate valgus moment without causing excessive concentration. Therefore, in order to avoid secondary ankle complications, we should not increase the tilt angle blindly.</p>

Taking ilium inner table to repair the articular surface defects of complex fracture of tibial plateau / 中国骨伤

<p><b>OBJECTIVE</b>To study the feasibility of application of ilium inner table to repair the articular surface defects of tibial plateau complex fractures.</p><p><b>METHODS</b>Twenty-three patients with tibial plateau complex fractures included 17 males and 6 females with an average age of 28.3 years old ranging from 18 to 51 years. The area of the articular surface defects ranged from 1 cmx2 cm to 3 cmx3 cm, averaged 6.7 cm2. Taking ilium inner table with periosteum after trimmed and implanting into the articular surface defect area with the concavity upward and drilled with diameter 1.5 mm Kirschner pin interval 3 to 4 mm. Bone grafting were placed under the ilium inner table and were fixed by T-shaped or L-shaped plate. The wounded limb were braked by plaster for 4 weeks after operation.</p><p><b>RESULTS</b>Twenty-three patients were followed-up for 8 months to 3 years, averaged 13.6 months. X-ray film showed solid union and the smooth articular surface in all cases. According to the Rasmussen evaluation system, the results were excellent in 11 cases, good in 8 cases,fair in 3 cases, poor in 1 case.</p><p><b>CONCLUSION</b>Taking ilium inner table to repair the articular surface defects of tibial plateau complex fractures is a good resolving measures. It can repaire major area of articular surface defects, restore the smooth articular surface and acquire good function of knee joint with easy to operate, less complications at donor area.</p>