无界域上具有记忆的非自治Plate方程随机吸引子的存在性

研究无界域上一类具有衰退记忆和加性噪声的非自治Plate方程解的长时间行为.利用一致估计验证了解的拉回渐近紧性,获得了其随机吸引子的存在性.

New direction for surgery:Super minimally invasive surgery

The top goal of modern medicine is treating disease without destroying organ structures and making patients as healthy as they were before their sickness.Minimally invasive surgery(MIS)has dominated the surgical realm because of its lesser invasiveness.However,changes in anatomical structures of the body and reconstruction of internal organs or different organs are common after traditional surgery or MIS,decreasing the quality of life of patients post-operation.Thus,I propose a new treatment mode,super MIS(SMIS),which is defined as“curing a disease or lesion which used to be treated by MIS while preserving the integrity of the organs”.In this study,I describe the origin,definition,operative channels,advantages,and future perspectives of SMIS.

Application of advanced platelet-rich fibrin for through-and-through bony defect during endodontic surgery:Three case reports and review of the literature

BACKGROUND The use of advanced platelet-rich fibrin(A-PRF)membranes for guided bone and tissue regeneration in through-and-through defects after endodontic surgery was explored in three cases.CASE SUMMARY Herein,three patients presented to the endodontic clinic suffering from apical periodontitis,associated with large bone resorption and related to previously endodontically treated teeth.Periapical surgery was indicated in these cases and the osteotomy site was covered by A-PRF membrane.Cone-beam computed tomography(CBCT)was used to assess the cases before and after the surgery.CONCLUSION Four months post-surgery,the recall CBCT scan showed complete obliteration of the osteotomy with newly formed bone.A-PRF membrane showed promising results and was an advantageous addition to surgical endodontic treatment.

Indocyanine green:The guide to safer and more effective surgery

In this editorial we comment on the article by Kalayarasan and co-workers published in the recent issue of the World Journal of Gastrointestinal Surgery.The authors present an interesting review on the use of indocyanine green fluo-rescence in different aspects of abdominal surgery.They also highlight future perspectives of the use of indocyanine green in mini-invasive surgery.Indo-cyanine green,used for fluorescence imaging,has been approved by the Food and Drug Administration and is safe for use in humans.It can be administered in-travenously or intra-arterially.Since its advent,there have been several advance-ments in the applications of indocyanine green,especially in the surgical field,such as intraoperative mapping and biopsy of sentinel lymph node,measurement of hepatic function prior to resection,in neurosurgical cases to detect vascular anomalies,in cardiovascular cases for patency and assessment of vascular ab-normalities,in predicting healing following amputations,in helping visualization of hepatobiliary anatomy and blood vessels,in reconstructive surgery,to assess flap viability and for the evaluation of tissue perfusion following major trauma and burns.For these reasons,the intraoperative use of indocyanine green has become common in a variety of surgical specialties and transplant surgery.Co-lorectal surgery has just lately begun to adopt this technique,particularly for perfusion visualization to prevent anastomotic leakage.The regular use of in-docyanine green coupled with fluorescence angiography has recently been pro-posed as a feasible tool to help improve patient outcomes.Using the best available data,it has been shown that routine use of indocyanine green in colorectal surgery reduces the rates of anastomotic leak.The use of indocyanine green is proven to be safe,feasible,and effective in both elective and emergency scenarios.However,additional robust evidence from larger-scale,high-quality studies is essential before incorporating indocyanine green guided surgery into standard practice.

Parallel pathways:A chronicle of evolution in rectal and breast cancer surgery

In this editorial,we have analyzed the historical evolution of rectal and breast cancer surgery,focusing on the progressive reduction of demolitive approaches and the increasing use of more conservative strategies,accompanied by a growing emphasis on perioperative treatments aimed at enhancing surgical outcomes.All of these changes have been made possible due to an increased awareness and understanding of oncological diseases and improved perioperative treatments.

Artificial Intelligence and Computer Vision during Surgery: Discussing Laparoscopic Images with ChatGPT4—Preliminary Results

Introduction: Ultrafast latest developments in artificial intelligence (ΑΙ) have recently multiplied concerns regarding the future of robotic autonomy in surgery. However, the literature on the topic is still scarce. Aim: To test a novel AI commercially available tool for image analysis on a series of laparoscopic scenes. Methods: The research tools included OPENAI CHATGPT 4.0 with its corresponding image recognition plugin which was fed with a list of 100 laparoscopic selected snapshots from common surgical procedures. In order to score reliability of received responses from image-recognition bot, two corresponding scales were developed ranging from 0 - 5. The set of images was divided into two groups: unlabeled (Group A) and labeled (Group B), and according to the type of surgical procedure or image resolution. Results: AI was able to recognize correctly the context of surgical-related images in 97% of its reports. For the labeled surgical pictures, the image-processing bot scored 3.95/5 (79%), whilst for the unlabeled, it scored 2.905/5 (58.1%). Phases of the procedure were commented in detail, after all successful interpretations. With rates 4 - 5/5, the chatbot was able to talk in detail about the indications, contraindications, stages, instrumentation, complications and outcome rates of the operation discussed. Conclusion: Interaction between surgeon and chatbot appears to be an interesting frontend for further research by clinicians in parallel with evolution of its complex underlying infrastructure. In this early phase of using artificial intelligence for image recognition in surgery, no safe conclusions can be drawn by small cohorts with commercially available software. Further development of medically-oriented AI software and clinical world awareness are expected to bring fruitful information on the topic in the years to come.

Does enhanced recovery after surgery programs improve clinical outcomes in liver cancer surgery?

Enhanced recovery after surgery(ERAS)programs have been widely applied in liver surgery since the publication of the first ERAS guidelines in 2016 and the new recommendations in 2022.Liver surgery is usually performed in oncological patients(liver metastasis,hepatocellular carcinoma,cholangiocarcinoma,etc.),but the real impact of liver surgery ERAS programs in oncological outcomes is not clearly defined.Theoretical advantages of ERAS programs are:ERAS decreases postoperative complication rates and has been demonstrated a clear relationship between complications and oncological outcomes;a better and faster posto-perative recovery should let oncologic teams begin chemotherapeutic regimens on time;prehabilitation and nutrition actions before surgery should also improve the performance status of the patients receiving chemotherapy.So,ERAS could be another way to improve our oncological results.We will discuss the literature about liver surgery ERAS focusing on its oncological implications and future investigations projects.

Transurethral prostate surgery in prostate cancer patients: A population-based comparative analysis of complication and mortality rates

Objective:Prostate cancer(PCa)patients might experience lower urinary tract symptoms as those diagnosed with benign prostatic hyperplasia(BPH).Some of them might be treated for their lower urinary tract symptoms instead of PCa.We aimed to test the effect of PCa versus BPH on surgical outcomes after transurethral prostate surgery,namely complication and mortality rates.Methods:Within the American College of Surgeons National Surgical Quality Improvement Program database(2011-2016),we identified patients who underwent transurethral resection of the prostate,photoselective vaporization,or laser enucleation.Patients were stratified according to postoperative diagnosis(PCa vs.BPH).Univariable and multivariable logistic regression models evaluated the predictors of perioperative morbidity and mortality.A formal test of interaction between diagnosis and surgical technique used was performed.Results:Overall,34542 patients were included.Of all,2008(5.8%)had a diagnosis of PCa.The multivariable logistic regression model failed to show statistically significant higher rates of postoperative complications in PCa patients(odds ratio:0.9,95%confidence interval:0.7-1.1;p=0.252).Moreover,similar rates of perioperative mortality(p=0.255),major acute cardiovascular events(p=0.581),transfusions(p=0.933),and length of stay of more than or equal to 30 days(p=0.174)were found.Additionally,all tests failed to show an interaction between post-operative diagnosis and surgical technique used.Conclusion:Patients diagnosed with PCa do not experience higher perioperative morbidity or mortality after transurethral prostate surgery when compared to their BPH counterparts.Moreover,the diagnosis seems to not influence surgical technique outcomes.

Imaging plate scanners calibration and the attenuation behavior of imaging plate signals

Based on previously reported work, we propose a new method for calibrating image plate(IP) scanners, offering greater flexibility and convenience, which can be extended to the calibration tasks of various scanner models. This method was applied to calibrate the sensitivity of a GE Typhoon FLA 7000 scanner. Additionally, we performed a calibration of the spontaneous signal attenuation behavior for BAS-MS, BAS-SR, and BAS-TR type IPs under the 20±1°C environmental conditions, and observed significant signal carrier diffusion behavior in BAS-MS IP. The calibration results lay a foundation for further research on the interaction between ultra-short, ultra-intense lasers and matter.

Results of the First 10 Cases of Coronary Bypass Surgery in Senegal

This is a review of the first 10 coronary artery bypass surgeries performed by the local team. The mean age was 62 years old [45 - 74]. The patients were predominantly male, with a M/F ratio of 4:1. Cardiovascular risk factors were mainly myocardial infarction (MI) (60%), hypertension (50%), obesity (40%) and diabetes (30%), with at least two risk factors per patient. Angina was the main symptom (80%). The average time from presentation to surgery was 8 months. The mean Euroscore 2 was 2.92 ± 1.65 [1.33 - 6.60]. Coronary angiography revealed an average of 2 lesions per patient, with 3-vessel involvement in 70% of cases: the Interventricular artery (IVA) (100%), the right coronary artery (90%) and the circumflex artery (70%). On echocardiography, the mean Left ventricular ejection fraction (LVEF) was 59% [33% - 76%]. All patients underwent median sternotomy with bypass grafting. The average duration of the cardiopulmonary bypass was 150 min [46 - 275 min];that of aortic clamping, 120 min [43 - 232 min]. The grafts used were internal thoracic artery (ITA) in 100% of cases (80% on the left and 20% on the right), and the great saphenous vein (GSV) in 60% of cases (50% on the left and 10 on the right). Double bypass was performed in 60% of cases, single bypass in 30% and triple bypass in 10%. The bypasses were performed on the IVA (100%), the middle lateral of the circumflex (30%) and the bisector (20%). The average time to extubation was 11 hours and the length of stay in the intensive care unit was 7 days [03 - 17 days]. One patient had a reoperation on Day 0 post-op. The average hospital stay was 13 days [06 - 27 days]. Complications occurred in nine of the patients (90%), with a predominance of infectious and neurological complications. Overall operative mortality was 3%, all in intensive care.

Modeling Geometrically Nonlinear FG Plates: A Fast and Accurate Alternative to IGA Method Based on Deep Learning

Isogeometric analysis (IGA) is known to showadvanced features compared to traditional finite element approaches.Using IGA one may accurately obtain the geometrically nonlinear bending behavior of plates with functionalgrading (FG). However, the procedure is usually complex and often is time-consuming. We thus put forward adeep learning method to model the geometrically nonlinear bending behavior of FG plates, bypassing the complexIGA simulation process. A long bidirectional short-term memory (BLSTM) recurrent neural network is trainedusing the load and gradient index as inputs and the displacement responses as outputs. The nonlinear relationshipbetween the outputs and the inputs is constructed usingmachine learning so that the displacements can be directlyestimated by the deep learning network. To provide enough training data, we use S-FSDT Von-Karman IGA andobtain the displacement responses for different loads and gradient indexes. Results show that the recognition erroris low, and demonstrate the feasibility of deep learning technique as a fast and accurate alternative to IGA formodeling the geometrically nonlinear bending behavior of FG plates.

Maxillofacial Surgery Education: Where Is It Heading?

Oral and maxillofacial surgery have a long history dating back to ancient civilizations such as the Egyptians. Since then, surgeons have treated craniofacial trauma and alveolodental fractures. In 1846, Hullihen performed a mandibular body osteotomy to correct prognathism, marking a significant milestone in the field. Over time, the specialty has evolved significantly. The field of craniofacial surgery has undergone several phases, including its involvement in conflicts during world wars and the treatment of craniofacial fractures and discrepancies. The process of learning and teaching specialties has evolved differently in various countries throughout the 20th century. Currently, there is no uniformity in the training and registration of specialized professionals, resulting in distinct scenarios. Considering the accessibility of scientific knowledge through technology and globalization, it is crucial to provide an objective overview of the current state of education in the field. This paper focuses on effective professional training as the primary subject of residency courses in this specialty. A proposal is presented for education, emphasizing the significance of providing quality professional training that is tailored to the specific legislation of each country.

Don’t forget emergency surgery! Lessons to learn from elective indocyanine green-guided gastrointestinal interventions

Fluorescence-based imaging has found application in several fields of elective surgery,but there is still a lack of evidence in the literature about its use in the emergency setting.Clinical trials have consistently shown that indocyanine green(ICG)-guided surgery can dramatically reduce the risk of postoperative complic-ations,length of in-hospital stay and total healthcare costs in the elective setting.It is well-known that emergency surgery has a higher complication rate than its elective counterpart,therefore an impelling need for research studies to explore,validate and develop this issue has been highlighted.The present editorial aims to provide a critical overview of currently available applications and pitfalls of ICG fluorescence in abdominal emergencies.Furthermore,we evidenced how the experience of ICG-fluorescence in elective surgery might be of great help in implementing its use in acute situations.In the first paragraph we analyzed the tips and tricks of ICG-guided cancer surgery that might be exploited in acute cases.We then deepened the two most described topics in ICG-guided emergency surgery:Acute cholecystitis and intestinal ischemia,focusing on both the advantages and limitations of green-fluorescence application in these two fields.In emergency situations,ICG fluorescence demonstrates a promising role in preventing undue intestinal resections or their entity,facilitating the detection of intestinal ischemic zones,identifying biliary tree anatomy,reducing post-operative complications,and mitigating high mortality rates.The need to improve its application still exists,therefore we strongly believe that the elective and routinary use of the dye is the best way to acquire the necessary skills for emer-gency procedures.

The interaction between a shaped charge jet and a single moving plate

Reactive armour is a very efficient add-on armour against shaped charge threats.Explosive reactive armour consists of one or several plates that are accelerated by an explosive.Similar but less violent acceleration of plates can also be achieved in a completely inert reactive armour.To be efficient against elongated jets,the motion of the plates needs to be inclined against the jet such that a sliding contact between the jet and the plates is established.This sliding contact causes a deflection and thinning of the jet.Under certain circumstances,the contact will become unstable,leading to severe disturbances on the jet.These disturbances will drastically reduce the jet penetration performance and it is therefore of interest to study the conditions that leads to an unstable contact.Previous studies on the interaction between shaped charge jets and flyer plates have shown that it is mainly the forward moving plate in an explosive reactive armour that is effective in disturbing the jet.This is usually attributed to the higher plate-to-jet mass flux ratio involved in the collision of the forward moving plate compared to the backward moving plate.For slow moving plates,as occurs in inert reactive armour,the difference in mass flux for the forward and backward moving plate is much lesser,and it is therefore of interest to study if other factors than the mass flux influences on the protection capability.In this work,experiments have been performed where a plate is accelerated along its length,interacting with a shaped charge jet that is fired at an oblique angle to the plate’s normal,either against or along the plate’s velocity.The arrangement corresponds to a jet interacting with a flyer plate from a reactive armour,with the exception that the collision velocity is the same for both types of obliquities in these experiments.The experiments show that disturbances on the jet are different in the two cases even though the collision velocities are the same.Numerical simulations of the interaction support the observation.The difference is attributed to the character of the contact pressure in the interaction region.For a backward moving plate,the maximum contact pressure is obtained at the beginning of the interaction zone and the contact pressure is therefore higher upstream than downstream of the jet while the opposite is true for a forward moving plate.A negative interface pressure gradient with respect to the jet motion results in a more stable flow than a positive,which means that the jet-plate contact is more stable for a backward moving plate than for a forward moving plate.A forward moving plate is thus more effective in disturbing the jet than a backward moving plate,not only because of the higher jet to plate mass flux ratio but also because of the character of the contact with the jet.

Performance analysis of single-focus phase singularity based on elliptical reflective annulus quadrangle-element coded spiral zone plates

Optical vortices generated by the conventional vortex lens are usually disturbed by the undesired higher-order foci,which may lead to additional artifacts and thus degrade the contrast sensitivity. In this work, we propose an efficient methodology to combine the merit of elliptical reflective zone plates(ERZPs) and the advantage of spiral zone plates(SZPs) in establishing a specific single optical element, termed elliptical reflective annulus quadrangle-element coded spiral zone plates(ERAQSZPs) to generate single-focus phase singularity. Differing from the abrupt reflectance of the ERZPs, a series of randomly distributed nanometer apertures are adopted to realize the sinusoidal reflectance. Typically, according to our physical design, the ERAQSZPs are fabricated on a bulk substrate;therefore, the new idea can significantly reduce the difficulty in the fabrication process. Based on the Kirchhoff diffraction theory and convolution theorem, the focusing performance of ERAQSZPs is calculated. The results reveal that apart from the capability of generating optical vortices,ERAQSZPs can also integrate the function of focusing, energy selection, higher-order foci elimination, as well as high spectral resolution together. In addition, the focusing properties can be further improved by appropriately adjusting the parameters, such as zone number and the size of the consisted primitives. These findings are expected to direct a new direction toward improving the performance of optical capture, x-ray fluorescence spectra, and forbidden transition.

Congenital Heart Disease Referred for Surgery: Analysis and Epidemiological Description in the Cardiology Department of CHU Ignace Deen

Introduction: Congenital heart disease includes all cardiac and vascular malformations. It accounts for approximately one third of all congenital malformations and is a public health problem, particularly in developing countries. The aim of this study was to analyze the epidemiological, clinical and paraclinical aspects of congenital heart disease. Methods: This was a retrospective descriptive and analytical study based on the records of 135 patients referred for surgery and followed up in the cardiology department of the Ignace Deen University Hospital, collected in November 2022. Results: Hospital prevalence was 5%. The mean age was 71 months, ranging from 1 month to 19 years. The age group over 24 months was the most represented (62%). The M/F sex ratio was 1.36. Urban origin was predominant (58%). The rate of children not attending school or dropping out was high (16%). Siblings with fewer than 4 children were the most common (88%). A heart murmur was the most frequent sign (78%), followed by cyanosis (36%) and heart failure (29%). The association between heart murmurs and CHD was proven with a p-value Conclusion: CHDs represent the main indication for paediatric cardiac surgery and follow-up (95%). We stress the importance of implementing a screening and management strategy for congenital heart disease.

Development and validation of a nomogram model for predicting the risk of gallstone recurrence after gallbladder-preserving surgery

Background:The high incidence of gallstone recurrence was a major concern for laparoscopic gallbladderpreserving surgery.This study aimed to investigate the risk factors for gallstone recurrence after gallbladder-preserving surgery and to establish an individualized nomogram model to predict the risk of gallstone recurrence.Methods:The clinicopathological and follow-up data of 183 patients who were initially diagnosed with gallstones and treated with gallbladder-preserving surgery at our hospital from January 2012 to January 2019 were retrospectively collected.The independent predictive factors for gallstone recurrence following gallbladder-preserving surgery were identified by multivariate logistic regression analysis.A nomogram model for the prediction of gallstone recurrence was constructed based on the selected variables.The C-index,receiver operating characteristic(ROC)curve and calibration curve were used to evaluate the predictive power of the nomogram model for gallstone recurrence.Results:During the follow-up period,a total of 65 patients experienced gallstone recurrence,and the recurrence rate was 35.5%.Multivariate logistic regression analysis revealed that the course of gallstones>2 years[odds ratio(OR)=2.567,95%confidence interval(CI):1.270-5.187,P=0.009],symptomatic gallstones(OR=2.589,95%CI:1.059-6.329,P=0.037),multiple gallstones(OR=2.436,95%CI:1.133-5.237,P=0.023),history of acute cholecystitis(OR=2.778,95%CI:1.178-6.549,P=0.020)and a greasy diet(OR=2.319,95%CI:1.186-4.535,P=0.014)were independent risk factors for gallstone recurrence after gallbladder-preserving surgery.A nomogram model for predicting the recurrence of gallstones was established based on the above five variables.The results showed that the C-index of the nomogram model was 0.692,suggesting it was valuable to predict gallstone recurrence.Moreover,the calibration curve showed good consistency between the predicted probability and actual probability.Conclusions:The nomogram model for the prediction of gallstone recurrence might help clinicians develop a proper treatment strategy for patients with gallstones.Gallbladder-preserving surgery should be cautiously considered for patients with high recurrence risks.

Are there sex-based disparities in cataract surgery?

AIM:To investigate sex-based differences in the occurrence of intra-operative and post-operative complications and associated visual outcomes following cataract surgery.METHODS:This was a retrospective study of patients who had phacoemulsification cataract surgery at the University of Colorado School of Medicine.Data collected included the patient’s health history,ocular comorbidities,operative and post-operative complications,and the post-operative best corrected visual acuity(BCVA).The data were analyzed using univariate and multivariable logistic regression with generalized estimating equations to account for the correlation of some patients having two eyes included in the study.RESULTS:A total of 11977 eyes from 7253 patients were included in the study.Ocular comorbidities differed by sex,with males having significantly higher percentages of traumatic cataracts(males 0.7%vs females 0.1%),prior ocular surgery(6.7%vs 5.5%),and mature cataracts(2.8%vs 1.9%).Conversely,females had significantly higher rates of pseudoexfoliation(2.0%vs 3.2%).In unadjusted analysis,males had higher rates of posterior capsular rupture(0.8%vs 0.4%)and vitreous loss(1.0%vs 0.6%),but this difference was not significant after adjustment for confounders.Males had a significantly increased risk of post-operative retinal detachment,but in multivariable analysis this was no longer significant.Males were significantly less likely to undergo post-operative neodymium-doped yttrium aluminum garnet(Nd:YAG)laser capsulotomy for posterior capsule opacification(OR=0.8,95%CI=0.7-0.9,P=0.0005).The BCVA was slightly worse for males pre-operatively;but post-operatively,both sexes exhibited similar visual acuity of Snellen equivalent 20/25.CONCLUSION:The study finds that in a cohort of patients presenting for cataract surgery,sex differences exist in pre-operative comorbidities and surgical characteristics that contribute to higher rates of some complications for males.However,observed surgical complication rates exhibit almost no difference by sex after adjusting for pre-operative differences and post-operative BCVA is similar between sexes.

Unsteady MHD Casson Nanofluid Flow Past an Exponentially Accelerated Vertical Plate:An Analytical Strategy

In this study,the characteristics of heat transfer on an unsteady magnetohydrodynamic(MHD)Casson nanofluid over an exponentially accelerated vertical porous plate with rotating effects were investigated.The flow was driven by the combined effects of the magnetic field,heat radiation,heat source/sink and chemical reaction.Copper oxide(CuO)and titanium oxide(TiO2)are acknowledged as nanoparticle materials.The nondimensional governing equations were subjected to the Laplace transformation technique to derive closed-form solutions.Graphical representations are provided to analyze how changes in physical parameters,such as the magnetic field,heat radiation,heat source/sink and chemical reaction,affect the velocity,temperature and concentration profiles.The computed values of skin friction,heat and mass transfer rates at the surface were tabulated for various sets of input parameters.It is perceived that there is a drop in temperature due to the rise in the heat source/sink and the Prandtl number.It should be noted that a boost in the thermal radiation parameter prompts an increase in temperature.An increase in the Prandtl number,heat source/sink parameter,time and a decrease in the thermal radiation parameter result in an increase in theNusselt number.The computed values of the skin friction,heat andmass transfer rates at the surface were tabulated for various values of the flow parameters.The present results were compared with those of previously published studies andwere found to be in excellent agreement.This research has practical applications in areas such as drug delivery,thermal medicine and cancer treatment.

Incidence of surgical site infection in minimally invasive colorectal surgery

BACKGROUND Surgical site infection(SSI)is a common complication of colorectal surgery.Minimally invasive surgery notably reduces the incidence of SSI.This study aimed to compare the incidences of SSI after robot-assisted colorectal surgery(RACS)vs that after laparoscopic assisted colorectal surgery(LACS)and to analyze associated risk factors for SSI in minimally invasive colorectal surgery.AIM To compare the incidences of SSI after RACS and LACS,and to analyze the risk factors associated with SSI after minimally invasive colorectal surgery.METHODS Clinical data derived from patients who underwent minimally invasive colorectal surgery between October 2020 and October 2022 at the First Affiliated Hospital of Soochow University were collated.Differences in clinical characteristics and surgeryrelated information associated with RACS and LACS were compared,and possible risk factors for SSI were identified.RESULTS A total of 246 patients(112 LACS and 134 RACS)were included in the study.Fortythree(17.5%)developed SSI.The proportions of patients who developed SSI were similar in the two groups(17.9%vs 17.2%,P=0.887).Diabetes mellitus,intraoperative blood loss≥100 mL,and incision length were independent risk factors for SSI.Possible additional risk factors included neoadjuvant therapy,lesion site,and operation time.CONCLUSION There was no difference in SSI incidence in the RACS and LACS groups.Diabetes mellitus,intraoperative blood loss≥100 mL,and incision length were independent risk factors for postoperative SSI.