ABSTRACT
Objective To investigate the biomechanical effects of interbody cage height on cervical spine during anterior cervical discectomy and fusion (ACDF) surgery,so as to provide references for selection of interbody cage.Metheds The finite element model of normal cervical spine (C2-7) was built and validated,and the cages with different height (5,6,7,8 mm) were implanted into C5-6 disc (cage 5,6,7,8 model).All the models were loaded with pure moment of 1.5 N · m to produce flexion,extension,lateral bending and axial rotation motions on cervical spine,and the effects of cage height on range of motion (ROM),facet joint stress,intervertebral pressure in cervical spine were investigated.Results The intervertebral angle at the fusion segment increased by 0.68° with per 1 mm-increase in height.The ROM in C5-6 after cage implantation was smaller than 0.44°.The influence of cage height on ROM in C4-5 was greater than that in C6-7,and the changes of ROM in non-fusion segments were smaller than 7.3％.The cage height variation had a smaller impact on the facet joint stress and intervertebral pressure.The stresses in the capsular ligament,cage and screw-plate system increased gradually with the increase of cage height,and the stresses in cage 6,7,8 models were much higher than those in cage 5 model.Conclusions For patients who need implanting fusion cage,the cage height should be 0-1 mm greater than the original intervertebral space height.
ABSTRACT
Objective Toinvestigate the molecular characteristics including antibiotic resistance,strain type,serotype,virulence,biofilm formation of Streptococcus pneumoniae isolated from Shanghai adult patients.Methods A total of 37 non-repetitive S.pneumoniae isolates causing community acquired and hospital acquired infections of adults were collected from Shanghai Huashan Hospital from January 2011 to December 2013.The inhibitory zone diameter or minimum inhibitory concentrations (MICs) of 9 antimicrobial agents (penicillin,vancomycin,erythromycin,clindamycin,levofloxacin,cefprozi,ceftriaxone,cefotaxime and linezolid) were determined by Kirby-bauer (K-B) method or Etest method;Serotypes were tested by polymerase chain reaction (PCR) and S.pneumoniae antisera agglutination;Genomic characteristics of different serotype strains were determined by pulsed field gel electrophoresis (PFGE)method;Multilocus sequence types (MLST) was used for strain type;Semi quantitative biofilm formation test was used for the biological membrane formation.Ten main pneumococcal virulence genes (cbpA,pspA,cps2A,lytA,nana,pavA,piaA,ply,psaA and spxB) were detected by PCR and gel electrophoresis.Statistical analysis was performed using Stata software and association statistics were tested using Fisher's exact test.Results The most frequent serotypes were 19F (13.5％),23 F (13.5％),14 (10.8％),19A (10.8％).The penicillin resistance rate was 64.9％.Serotypes 19 F,19A and 23 F were significantly associated with penicillin resistance (x2 =5.89,P =0.015) and the isolates belonged to these serotypes were all multi-drug resistant (MDR).ST81 and ST271 showed high resistance rates to several antibiotics including penicillin (x2 =4.57,P =0.033).Biofilm formation was significantly associated with serotypes 19A (x2 =5.55,P =0.018) and strain type ST320 (x2 =4.33,P =0.037),but not associated with penicillin resistance (x2 =0.16,P =0.686).Virulence gene lytA,pavA,ply,psaA,spxB were found in all isolates.Conclusions Penicillin resistance rate of S.pneumoniae in adult is rising.Specific serotype,epidemic clone and antibiotic resistance are closely related,and can provide the basis for the infection control.The virulence factors such as PspA will be the new targets for vaccine development to reduce S.pneumoniae infection in the future.