Objective To understand the current situation and influencing factors of work-related musculoskeletal disorders (WMSDs) in medical staff in Beijing City. Methods A total of 2 687 medical staff were selected as the research subjects using the multi-stage sampling method. The current situation of WMSDs and occupational stress, anxiety symptoms, depressive symptoms, and insomnia symptoms were investigated using the Musculoskeletal Disorders Questionnaire, the Core Occupational Stress Scale, the Generalized Anxiety Disorder Scale, the Patient Health Questionnaire Depression Scale, and the Self-Sleep Management Questionnaire. The Max-Min Hill-Climbing algorithm was used to construct a Bayesian network model to analyze the influencing factors and internal relationships of WMSDs and to conduct reasoning and prediction of the model. Results The prevalence of WMSDs among the research subjects was 88.9%. Binary logistic regression analysis was used to identify age, educational level, personal monthly income, anxiety symptoms, depressive symptoms, insomnia symptoms, prolonged forward-head desk work, and prolonged static posture work to construct the Bayesian network model. The model consisted of nine nodes and eleven directed edges. Prolonged static posture work, prolonged forward-head desk work, and anxiety symptoms were directly related to WMSDs. Age and educational level were indirectly related to WMSDs through their influence on prolonged forward-head desk work. Depression symptoms were indirectly associated with WMSDs through their influence on anxiety symptoms. The model's prediction accuracy was 90.5%. Conclusion The prevalence of WMSDs among medical staff in Beijing City is relatively high. Prolonged static posture work, prolonged forward-head desk work, and anxiety symptoms may directly increase the risk of developing WMSDs.

Objective To investigate the relationship between lesion size of solitary bone cyst ( SBC) and pathological fracture of calcaneus, so as to provide references for the treatment of SBC. Methods The three dimensional (3D) finite element model of foot and ankle was established based on CT images. Four models with gradient spherical bone defects were constructed in the focal area to simulate different SBC lesion sizes, and the biomechanical characteristics of calcaneus in different gait phases were analyzed. Results With the increasement of SBC size, the kinematics of calcaneus did not change significantly, but the peak stress of calcaneus increased gradually. When the SBC size exceeded 75% of the calcaneal width, the stress in calcaneal sulcus and cortical bone below SBC increased by 1. 48 times and 7. 74 times, respectively. Conclusions The risk of pathological fracture increases when the SBC diameter exceeds 75% of the calcaneal width, and early surgical intervention should be recommended. The calcaneal sulcus and the cortex bone below SBC are stress concentration regions and can be used as important areas to evaluate pathological fractures.

Objective : To explore the optimal pulse width of ultra-short pulse Er : YAG laser for improving dentin bonding strength． Methods : Forty isolated third molars were prepared in the shape of wedge defect in the neck，and the coronal plane was taken．The samples were randomly divided into 5 groups : group G0 was blank group，and groups G1-G4 were treated with 30 MJ，20 Hz Er : YAG laser，and the pulse width was set to 30，40，50 and 60 μs， respectively．The morphology of dentin surface was observed by scanning electron microscopy (SEM) ，and the ratio of calcium to phosphorus was detected by energy dispersive X-ray spectroscopy ( EDX) ．The shear bond strength ( SBS) of each group and the fracture form under the type microscope were tested by the universal mechanical tes- ting machine．The effect of different pulse width on improving dentin bonding strength was evaluated. Results : SEM observation showed that the stained layer was removed after laser treatment with different pulse widths，and the den- tin tubules were opened to different degrees．The calcium-phosphorus ratio of dentin after laser treatment increased， and the difference of calcium-phosphorus ratio in G2 group was statistically significant (P＜0. 05) ．The mean value of SBS after the cold and hot cycle experiment was G2 ＞G3 ＞G1 ＞G4 ＞G0，and the difference between G2 group and G0 group，G1 group，G3 group and G4 group are statistically significant (P ＜0. 05 ) ．The difference between group G0 and groups G1，G2，G3 and G4 was statistically significant (P＜0. 05) ．The main fracture forms of each group were type 1 and type 3． Conclusion The 30 MJ，20 Hz Er : YAG laser pulse width of 40 μs can significantly improve the bond strength of dentin.

This study aims to analyze the biomechanical stability of Magic screw in the treatment of acetabular posterior column fractures by finite element analysis. A three-dimensional finite element model of the pelvis was established based on the computed tomography (CT) and magnetic resonance imaging (MRI) data of a volunteer and its effectiveness was verified. Then, the posterior column fracture model of the acetabulum was generated. The biomechanical stability of the four internal fixation models was compared. The 500 N force was applied to the upper surface of the sacrum to simulate human gravity. The maximum implant stresses of retrograde screw fixation, single-plate fixation, double-plate fixation and Magic screw fixation model in standing and sitting position were as follows: 114.10, 113.40 MPa; 58.93, 55.72 MPa; 58.76, 47.47 MPa; and 24.36, 27.50 MPa, respectively. The maximum stresses at the fracture end were as follows: 72.71, 70.51 MPa; 48.18, 22.80 MPa; 52.38, 27.14 MPa; and 34.05, 30.78 MPa, respectively. The fracture end displacement of the retrograde tension screw fixation model was the largest in both states, and the Magic screw had the smallest displacement variation in the standing state, but it was significantly higher than the two plate fixations in the sitting state. Magic screw can satisfy the biomechanical stability of posterior column fracture. Compared with traditional fixations, Magic screw has the advantages of more uniform stress distribution and less stress, and should be recommended.
Biomechanical Phenomena ; Bone Plates ; Bone Screws ; Finite Element Analysis ; Fracture Fixation, Internal/methods* ; Fractures, Bone/surgery* ; Humans ; Spinal Fractures

Objective: To investigate the application of Symptom Checklist-90 (SCL-90) in Chinese nurses. Methods: We performed a literature search for articles in Chinese on the mental health of nurses investigated using the SCL-90 that were published from January 2007 to December 2016. A total of 129 articles were included, involving 178 groups of valid samples as well as 36316 subjects in 27 provinces or cities in China. The metafor package of R 3.2.1 software and Excel were used for meta-analysis and data statistics. Results: Heterogeneity was identified for the nine factors included in the literature data (Q test: P<0.05; I² test >40%) , so a random effects model was used. For all factors except interpersonal relationship factor, the 95% confidence intervals of the pooled effect sizes did not include 0. For all factors except interpersonal relationship factor (Egger test: P<0.05) , no significant asymmetry or incompleteness appeared in the funnel plots. The fail-safe number of each factor was much larger than 5k+10. The merger scores and mean values of nine factors were higher than the national norm. Conclusion The SCL-90 is widely used in the study of mental status of Chinese nurses, but the SCL-90 norm for nurses is lacking.

Objective:To evaluate the effects of platform switching and platform matching system on the marginal bone resorption a-round implant.Methods:Randomized controlled trials (RCTs)that compared marginal bone loss around platform-switched implants with platform matched prostheses were selected from PubMed,EMbase,CBM,CNKI and other electronic databases supplemented by hand search and retrospective collection of literature published or unpublished between 1 991 -201 4.The literature based on inclusion and exclusion criteria was screened by 2 revieweres independently,the quality of the included studies was evaluated,the data were extracted using RevMan 5.2 software for Meta-analysis.Results:1 4 studies with 1 331 implants were included.Meta-analysis showed that peri-implant bone resorption in the platform switching group was significantly less than that in the platform matching group[MD =-0.51 ,95% CI:(-0.72 -0.30),P <0.01 ].Subgroup analysis showed that the implant-abutment diameter difference >0.45 mm (unilateral)was more favorable to implant marginal bone preservation.Conclusion:The present data suggest that platform-switched technology is more conducive to implant bone preservation than platform-matched method.

Objective To investigate the effect of TiO2 nanotube arrays covalently modified by recombinant human bone morphogenetic protein-2(rhBMP-2) on the early bioactivity of mesenchymal stem cells(MSC) in vitro and to provide experimental evidence for the biochemical modification of titanium implants.Methods In the experiment group,double titanium nanotube arrays were prepared by anodization,and were chemically grafted with rhBMP-2.Mechanically polished pure titanium was used as blank control group,and titanium dioxide nanotubes was used as negative control A group,and titanium dioxide nanotubes + carbonyldiimidazole as negative control B group.Field emission scanning electron microscope(FE-SEM) and X-ray photoelectron spectroscopy(XPS) were used to detect the morphology and physicochemical properties of the experiment group,blank control group and the negative control group.Cell adhesion on the specimen surface of the experiment group,blank control group and negative control group on the 1st day was tested.Cell proliferation on the 1st,3rd and 5th day and alkaline phosphatase activity on the 5th,7th and 11th day was also tested.Results FE-SEM showed that the surface of titanium nanotubes loaded with rhBMP-2 possessed visible miliary particulate matter.XPS showed that nitrogen peak in the group of titanium nanotubes loaded with rhBMP-2 was significantly greater that those in the other groups.FE-SEM showed that the cells on the surface of the experimental group on the 1st day spread well,better than those in the control group and negative control group.Cell proliferation activity on the 1st day in different groups was not obvious(P＞0.05),the A value of the experimental group on the 3rd and 5th day (3.295±0.153,3.823±0.059) were significantly higher than those in the control group(2.479±0.064,3.131±0.096) and negative control A group(2.715±0.075,3.371±0.047) and negative control B group(2.756±0.132,3.637±0.047)(P＜0.05).Alkaline phosphatase activity on the 5th,7th and 1 1th day in the experimental group (0.0477 ± 0.0287,0.0615 ± 0.0016,0.0667 ± 0.0018) were better than those in the control group,negative control A group and negative control B group(P＜0.05).Conclusions Titanium nanotube arrays can be loaded with rhBMP-2 by biochemical methods and have good biocompatibility.