BACKGROUND:Pedicle screw is a good means for internal fixation and has been widely used in clinical practice. OBJECTIVE:To explore the factors influencing the fixation strength of pedicle screws, and to provide biomechanical basis for clinical selection of pedicle screws. METHODS:The recently published studies addressing the biomechanics of pedicle screws were retrieved, and those focusing on the influence of pedicle screw geometry, implantation technique, pedicle anatomical factor, vertebral bone density, screw manufacturing process and material properties on the fixation strength of pedicle screws were retrospectively analyzed, thus providing theoretical basis for clinical treatment. RESULTS AND CONCLUSION:Results showed that, the appearances of pedicle screws such as screw size, screw thread form and fatigue property are the main factors associated with the fixation strength, in addition, vertebral bone density, screw manufacturing process and material properties cannot be ignored. The screw withdrawal force and stability can be improved by increasing screw diameter, improving screw design, strengthening bone density, and modifying operations.

ObjectiveTo investigate the relationship between the expression of triggering receptor1 present on myeloid cells ( TREM-1 ) in intestinal tissue and intestinal barrier dysfunction in severe acute pancreatitis (SAP). MethodsSixty-four male Wistar rats were randomly (random number) divided into sham operation group ( SO group, n = 32) and SAP group ( n = 32 ). The SAP model was established by retrograde injection of 5％ sodium deoxycholate into bile-pancreatic duct. Specimens from blood and intestinal tissue were collected 2, 6, 12 and 48 hours after modeling. The levels of D-lactate, diamine oxidase (DAO) and endotoxin in serum were measured with an modified spectro-photometric method. The expressions of TREM-1, IL-1β and TNF-αt mRNA in terminal ileum were detected by RT-PCR. All data were processed with SPSS version 16. 0 package to make one-way ANOVA and Spearman correlation analysis. ResultsThe serum levels of D-lactate, DAO and endotoxin were significantly increased at all intervals in SAP group compared with SO group ( P ＜ 0. 05 ). The expressions of TREM-1, IL-1β and TNF-α mRNA in terminal ileum of rats in SAP group at all intervals were significantly higher than those in SO group (P ＜ 0. 05 ). The expression of TREM-1 mRNA was positively correlated with expressions of IL-1 β and TNF-α mRNA ( r = 0. 956, P = 0. 044; r = 0. 986, P = 0. 015 ), but correlation was not found between expressions of IL-1β mRNA and TNF-α mRNA ( P = 0. 133 ). ConclusionsThe expression of TREM-1mRNA in intestinal tissue of rats with SAP is elevated, leading to the release of inflammatory cytokines and intestinal mucosal injury, indicating TREM-1 might play an important role in the genesis of intestinal barrier dysfunction in rats with SAP.

Objective To explore the possibility for preventing the underwater blast injuries. Methods Fifty rabbits were divided into two groups: protection and control groups. The animals were placed at the rang of 5.0m to 17.5m far from the explosion point. 0.2kg of TNT Explosives was placed 3 meters under water. Physical parameters of blast wave were measured using pressure transducers. At 6 hours after injury, the mortality rate and morphological alternations were observed. Results The safe devices were shown to be effective against underwater blast injuries. Most of the animals had no or mild pulmonary and intestinal injuries. The whole injury severity was reduced by 2 to 3 degrees with our own made device. Conclusion Our safe device could be used to protect against underwater blast injueirs.

Objective To investigate the expression of DNA methyltransferases (DNMTs) in liver cancer and its clinical significance. Methods The specimens of liver cancer tissues, adjacent tissues, cirrhotic tissues and chronic hepatitis tissues were collected from 50 patients who received radical resection at the First Affiliated Hospital of Sun Yat-Sen University from July 2007 to April 2008. The mRNA and protein expressions of DNMT1,DNMT3a and DNMT3b in liver cancer tissues, adjacent tissues, cirrhotic tissues and chronic hepatitis tissues were detected by real-time quantitative PCR and immunohistochemical staining. The mRNA expression of DNMTs in the liver cancer tissues was compared with those in the adjacent tissues, cirrhotic tissues and chronic hepatitis tissues by using t test and Mann-Whitney U test. The correlation between the protein expression of DNMTs in the liver cancer tissue and the clinicopathological features was analyzed by chi-square test or Fisher exact test, and the tumor-free survival time was analyzed by using Kaplan-Meier method and the difference in tumor-free survival rate between different patients was analyzed by Log-rank test. Results The mRNA expressions of DNMT1, DNMT3a and DNMT3b in the liver cancer tissue were 2.57, 2.29 and 4.86 times higher than those in the adjacent tissues (t = 3.94, 2. 72, 4. 06, P ＜ 0.05 ). The mRNA expressions of DNMT1, DNMT3a and DNMT3b were 2.38,2.14 and 4.66 times higher than those in the cirrhotic tissues, and 6.12, 4.58 and 12.99 times higher than those in the chronic hepatitis tissues. The mRNA expressions of DNMT1, DNMT3a and DNMT3b in the liver cancer tissue were significantly higher than those in the cirrhotic tissues and chronic hepatitis tissues ( U = 587.5,730. 0,562.5; 65.5, 64.5, 71.0, P ＜ 0.05). The protein expression of DNMT1 was correlated with the size, number,TNM stages and vascular invasion of tumors ( x2 = 4.08, 5.95, 4.08, P ＜ 0.05 ). The protein expression of DNMT3a was correlated with the size, number and TNM stages of tumors (x2 = 4.08, 5.95, 4.08, P ＜ 0.05 ).The mean tumor recurrence time of patients with low expressions of DNMT1 and DNMT3a were 9.4 and 8.7 months, which were significantly longer than 5.0 and 3.2 months of those with high expressions of DNMT1 and DNMT3a (x2 =3.89, 9.91, P＜0.05). Conclusions DNMTs play an important role in hepatocarcinogenesis.High expressions of DNMT1 and DNMT3a are correlated with the postoperative recurrence of liver cancer, which are valuable prognostic factors for liver cancer.

Objective To discuss the feasibility and long-term effect of free latissimus dorsi muscle flap in repair of severe lower extremity injury in children. Methods From July 1999 to June 2004, nine child patients (at age of 6-13 years) with severe lower extremity injury involving soft tissue defects a-round the calf and the foot associated with complex open fractures, bare dislocation, and injury of the nerve, tendon and artery were repaired with free latissimus donsi flap, with flap area ranging from 30 cm ×12 cm to 10 cm × 5 cm. Results All the latissimus dorsi flaps survived, with success rate of 100%. A follow-up for 4-9 years showed that the flap had sound shape and function and normal blood supply, without significant influence on donor area. Conclusion Latissimus dorsi flap has advantages of constant anatomical site, abundant blood supply, massive area, strong anti-infection ability and less in-fluence on donor area and hence is an ideal method for repairing severe lower extremity injury in children.

Objective To explore the preparation of liposomal clodronate and investigate its inducing effects on the apoptosis of peritoneal macrophages in rats after severe acute pancreatitis (SAP).Methods Liposomal clodronate was prepared by means of thin film. SAP rat model was established by retrograde injection of 5% sodium taurocholate into the pancreatic duct. The peritoneal macrophages were obtained from SAP rats. After exposure to different doses of liposomal clodronate (50, 100,150 μl), the PM proliferation was determined by MTT colourimetry. The apoptosis of PM was measured by flow cytometry and agarose gel electrophoresis, respectively. Results The prepared liposomal clodronate had a suitable encapsulation efficiency of clodronate (5.8%) with an average size of 200 nm. The spherical shape of liposome was confirmed by transmission electron microscope. Exposed to liposomal clodronate of different doses resulted in a obvious growth depression (P＜0.01). The apoptotic rate of the PM was (10.32±0.34) %, (18.16±0.49)% and (29.87±0.35)% in three different dose groups and the difference was marked (P＜0.01). 1.2% of agarose gel electrophoresis of DNA extracted from apoptotic macrophages induced by liposomal clodronate showed clearer and characteristic ladder following the liposomal clodronate concentration. Conclusion Liposomal clodronate has a definite effect on peritoneal macrophages in SAP rats.

Objective To investigate the expression of DNA methyltransferases ( DNMTs) in hilar cholangiocarcinoma and its clinical significance.Methods A total of 150 samples of cholangetic tissues were collected from 111 patients with hilar cholangiocarcinoma ( cholangiocarcinoma group) and 39 patients with choledochocele ( control group) at the First Affiliated Hospital of Sun Yat-Sen University from April 1997 to March 2007.A tissue chip containing the samples of hilar cholangiocarcinoma and choledochocele was prepared.Expressions of DNMT1,DNMT3a and DNMT3b were detected by the immunohistochemical staining. Differences in the protein expressions of DNMTs in the cholangiocarcinoma group and the control group were compared,and the correlation between DNMTs protein expressions and clinicopathological features was analyzed.All data were analyzed by using the chi-square test or Fisher exact probability.The survival curve was drawn by using the Kaplan-Meier method and the survival rate was compared by using the Log-rank test.Results The rates of high protein expressions of DNMT1 and DNMT3b were 54.1％ (60/111) and 47.7％ (53/111) in the cholangiocarcinoma group, which were significantly higher than 28.2％ ( 11/39) and 23.1％ ( 9/39) in the control group　( x2 =7.740,7.240,P ＜0.05). The high protein expression of DNMT1 was correlated with-the Bismuth-Corlette classification and T staging of the tumor ( x2 =12.200, 17.800,P ＜0.05) ; there was no significant difference in the high protein expressions of DNMT3a in the cholangiocarcinoma group and the control group ( x2 =3.370.P ＞0.05 ) ; while the high protein expressions of DNMT3b was correlated with the Bismuth-Corlette classification (x2 =8.300,P ＜ 0.05 ),but not with the T staging. Sixty-six patients received hilar cholangiocarcinoma resection,and 42 of them were followed up.The median postoperative survival time of patients with low protein expression of DNMT1 was 23.9 months,which was significantly longer than 11.8 months of patients with high protein expression of DNMT1 (x2 =3.980,P ＜ 0.05).Conclusions DNMT1 and DNMT3b with high protein expression might play important roles in the carcinogenesis and development of hilar cholangiocarcinoma.There is an obvious relationship between the expression of DNMT1 and postoperative survival time of patients with hilar cholangiocarcinoma,and DNMT1 might be a valuable prognostic factor for hilar cholangiocarcinoma.

Objective To develop a device for stretch-induced injury to cultured cells and measure the injury parameters.It makes possible to observe the changes of cell configuration and function directly after injury. Methods The device was developed based on aero-dynamical principle,and consisted of mini-type air compressor,electromagnetic valve,pressure transmitter,PGA amplifier,A/D converter and computer.The computer can accurately control the injury parameters.A new method and device were first introduced to measure the deformation rate and deformation degree of silastic membrance in the stretch induced cultured cell injury process.The device controlled by the computer was used to cause the astrocyte injury.The degree of cell injury was assessed qualitatively by electron microscopy,and quantitatively by lactate dehydrogenase(LDH) enzyme release and trypan blue staining.Results The experiment results showed that the injury of different levels could be reproduced by our device under the injury parameters we set.Conclusion The injury device and the measuring system meet the requirements of our design.The results suggested that the new device and the method were much better than those reported in foreign literature.It has the advantages of simple and convenient manipulation,high precision and real-time processing.It can be used for the cell-level experiment research.

Objective To study the mechanics of moderate and severe brain injury of pedestrians in road traffic accident by establishing the virtual model of impact occipital bone injury.Methods The clinical data were used to analyze comlnon mode and characteristics of moderate and severe brain injury of pedestrians.Then,the corresponding finite element model built by using Hypermesh software was used to to analyze the changes of intracranial pressures and compare with injury characteristics by using Ls-Dyna soft-ware. Results The conlmon injury mode of moderate and severe brain injury of pedestrians wag the con-tact impact of occiputal part,characterized by"eontrecoup injury",mainly including subdural hemorrhage,extradural hemorrhage and contusion in the opposite parts to the impact point.The simtdation resuhs showed that when the impact was at right occiputal bone.the peak value of condensing force decreased from the right occipital lobe.to the left frontal lobe,while the peak value of tension increased gradually and reached maximum at the surface of left frontal lobe. Conclusions Moderate and severe brain injury of pedestrian is commonly caused by impacting the occiputal bone in road traffic accident.The tension deformation in frontal or temporal lobes and the distribution of vessels in grey matter may be main biomeehanies leading to "contrecoup injury".

Objective To study the effects of elodronate-liposome on inducing apoptosis of alve-olar macrophages from rats with acute neetotizing pancreatitis (ANP).Methods The AMs of eight rats with ANP were isolated, purified then incubated from broehoalveolar lavage by the differing rates of attachment of the various cell types in a forty-well cell culture plate.Then they were randomized in-to five groups including control group,blank liposome group( 50 μ1, 100 μ1),clodronate-liposome group (50μ1,100μ1).Values of OD were determined by MTT.AO fluorescence and haematoxylin dye were employed to determine the apoptosis of the AMs.Results There were no significant differences be-tween control group and blank liposome group(50 μ1, 100 μ1).Significant differences were found be-tween control group and clodronate-liposome group(50 μ1, 100 μ1).There were no marked differences between blank liposome group(50μ1, 100 μ1)and clodronate-liposome group(50 μ1,100μ1).AO fluo-rescence and haematoxylin dye were available to define the apoptosis of the AMs.Conclusion Clodr-onate-liposome can effectively induce the apoptosis of the AMs.