Reducing retraction forces with tactile feedback during robotic total mesorectal excision in a porcine model.

Excessive tissue-instrument interaction forces during robotic surgery have the potential for causing iatrogenic tissue damages. The current in vivo study seeks to assess whether tactile feedback could reduce intraoperative tissue-instrument interaction forces during robotic-assisted total mesorectal excision. Five subjects, including three experts and two novices, used the da Vinci robot to perform total mesorectum excision in four pigs. The grip force in the left arm, used for retraction, and the pushing force in the right arm, used for blunt pelvic dissection around the rectum, were recorded. Tissue-instrument interaction forces were compared between trials done with and without tactile feedback. The mean force exerted on the tissue was consistently higher in the retracting arm than the dissecting arm (3.72 ± 1.19 vs 0.32 ± 0.36 N, p < 0.01). Tactile feedback brought about significant reductions in average retraction forces (3.69 ± 1.08 N vs 4.16 ± 1.12 N, p = 0.02), but dissection forces appeared unaffected (0.43 ± 0.42 vs 0.37 ± 0.28 N, p = 0.71). No significant differences were found between retraction and dissection forces exerted by novice and expert robotic surgeons. This in vivo animal study demonstrated the efficacy of tactile feedback in reducing retraction forces during total mesorectal excision. Further research is required to quantify the clinical impact of such force reduction.

Technical Feasibility, Outcomes, and Patient Satisfaction After Needlescopic and Laparoscopic Bariatric Surgery: a Randomized Study.

BACKGROUND: Needlescopic instruments create a 3-mm incision and may result in less pain and superior cosmesis. There is limited understanding of the effectiveness of needlescopic instruments in patients with a body mass index (BMI) > 35 kg/m2. We report perioperative outcomes and perception of body image with use of needlescopic instruments after bariatric surgery. METHODS: Laparoscopic bariatric procedures were performed on 30 adults at a single academic medical center from January to December 2017. Patients were randomized to conventional laparoscopy (LAP) or needlescopic (NEED) surgery. The Multidimensional Body-Self Relations Questionnaire (MBSRQ) and Patient Scar Assessment Questionnaire (PSAQ) were completed at 6 months and 1 year. Univariate analysis was performed on perioperative outcomes and survey scores. RESULTS: Surgery was completed on patients in the LAP group (N = 13) and compared to the NEED group (N = 17). The mean BMI was 41.4 kg/m2 LAP and 41.1 kg/m2 NEED. The most common procedure was Roux-en-Y gastric bypass (RYGB), with 13 RYGB in LAP and 12 RYGB in NEED (P = 0.76).The operative time was not significantly different between the LAP and the NEED group (209.5 ± 66.1 vs 181.9 ± 58.1 min, P = 0.48). There was no leak or mortality in the 30-day follow-up period. Within MBSRQ, the patient's appearance self-evaluation score was similar between LAP and NEED (2.5 ± 0.6 vs 2.4 ± 0.6, P = 0.61). Within PSAQ, the mean satisfaction score for incision appearance was also similar between LAP and NEED (16.1± 2.9 vs 15.4 ± 4.6, P = 0.85). Incision-related perceptions remained consistent at 6 months and 1 year after bariatric surgery. CONCLUSIONS: Needlescopic instruments are safe and a viable alternative to use during bariatric surgery. Appearance and perception of scar were similar between groups. Further studies with needlescopic instruments should include patients with a BMI > 35 kg/m2 and compare additional factors associated with body image.

Risk factors for readmission for early small bowel obstruction following laparoscopic Roux-en-Y gastric bypass: an MBSAQIP analysis.

BACKGROUND: Small bowel obstruction (SBO) following laparoscopic Roux-en-Y gastric bypass (LRYGB) is associated with significant morbidity. OBJECTIVES: To evaluate the rate of and risk factors for readmission for SBO within 30 days of LRYGB. SETTING: Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program (MBSAQIP)-accredited centers. METHODS: This is a retrospective study using the MBSAQIP database. A query was performed from 2015-2018 for patients who underwent LRYGB and required readmission for SBO. Those who had a reoperation, intervention, readmission, or expired from causes other than SBO were excluded. Descriptive, bivariate, and binary logistic regression analyses were performed. RESULTS: Among 184,660 patients undergoing LRYGB, 1189 (.64%) required readmission due to SBO. Among the readmission cases, 978 (82.5%) were identified as having intestinal obstruction (unspecified), 108 (9.1%) incisional hernia, and 100 (8.4%) internal hernia. Among these cases, 69% had a reoperation and 1.3% expired during the 30-day period. From a logistic regression model, parameters independently associated with an increased risk for readmission for early SBO include being female (adjusted odds ratio [AOR], 1.53) or black (AOR, 1.41) and having gastroesophageal reflux (AOR, 1.35), a history of myocardial infarction (AOR, 1.76), a history of deep vein thrombosis (AOR, 1.73), previous obesity surgery/foregut surgery (AOR, 1.79), a robotic-assisted procedure (AOR, 1.23), concurrent hiatal hernia repair (AOR, 1.66) and adhesiolysis (AOR, 1.42). CONCLUSION: The rate of readmission for early SBO following LRYGB was less than 1%. The majority of these cases required reoperation. The increased intraoperative complexity of LRYGB is associated with an increased risk of readmission due to early SBO.

Analysis of Early Job Market Experiences and Perceptions Among Bariatric Surgery Fellowship Graduates and Bariatric Surgery Program Directors.

PURPOSE: Over the past decade, an increasing number of bariatric surgeons are trained in fellowships annually despite only a modest increase in nationwide bariatric surgery volume. The study surveys the bariatric surgery job market trend in order to inform better career-choice decisions for trainees interested in this field. MATERIALS AND METHODS: A national retrospective cohort survey over an 11-year period was conducted. Bariatric surgery fellowship graduates from 2008 to 2019 and program directors (PDs) were surveyed electronically. Univariate analysis was performed comparing responses between earlier (2008-2016) and recent graduates (2017-2019). RESULTS: We identified a total of 996 graduates and 143 PDs. Response rates were 9% and 20% respectively (n = 88, 29). Sixty-eight percent of graduates felt there are not enough bariatric jobs for new graduates. Seventy-nine percent of PDs felt that it is more difficult to find a bariatric job for their fellows now than 5-10 years ago. Forty-eight percent of PDs felt that we are training too many bariatric fellows. Seventy-seven percent of all graduates want the majority of their practice to be comprised bariatric cases; however, only 42% of them reported achieving this. In the univariate analysis, recent graduates were less likely to be currently employed as a bariatric surgeon (64% vs. 86%, p = 0.02) and were less satisfied with their current case volume (42% vs. 66%, p = 0.01). CONCLUSIONS: The temporal increase in bariatric fellowship graduates over the past decade has resulted in a significant decline in the likelihood of employment in a full-time bariatric surgical practice and a decline in surgeons' bariatric case volumes.

Screen-Based Simulation for Training and Automated Assessment of Teamwork Skills: Comparing 2 Modes With Different Interactivity.

INTRODUCTION: The need for teamwork training is well documented; however, teaching these skills is challenging given the logistics of assembling individual team members together to train in person. We designed 2 modes of screen-based simulation for training teamwork skills to assess whether interactivity with nonplayer characters was necessary for in-game performance gains or for player satisfaction with the experience. METHODS: Mixed, randomized, repeated measures study with licensed healthcare providers block-stratified and randomized to evaluation-participant observes and evaluates the team player in 3 scenarios-and game play-participant is immersed as the leader in the same 3 scenarios. Teamwork construct scores (leadership, communication, situation monitoring, mutual support) from an ontology-based, Bayesian network assessment model were analyzed using mixed randomized repeated measures analyses of variance to compare performance, across scenarios and modes. Learning was measured by pretest and posttest quiz scores. User experience was evaluated using χ2 analyses. RESULTS: Among 166 recruited and randomized participants, 120 enrolled in the study and 109 had complete data for analysis. Mean composite teamwork Bayesian network scores improved for successive scenarios in both modes, with evaluation scores statistically higher than game play for every teamwork construct and scenario (r = 0.73, P = 0.000). Quiz scores improved from pretest to posttest (P = 0.004), but differences between modes were not significant. CONCLUSIONS: For training teamwork skills using screen-based simulation, interactivity of the player with the nonplayer characters is not necessary for in-game performance gains or for player satisfaction with the experience.

Indications, Operative Techniques, and Outcomes for Revisional Operation Following Mini-Gastric Bypass-One Anastomosis Gastric Bypass: a Systematic Review.

In addition to being a relatively reversible and less complex operation, mini-gastric bypass-one anastomosis gastric bypass (MGB-OAGB) has demonstrated comparable weight loss and metabolic improvement rates with Roux-en-Y gastric bypass (RYGB). However, surgical strategies for managing its failures and late complications were poorly defined. This article aims to review the indications, operative techniques, and outcomes for revisional surgery following MGB-OAGB. A systematic review was performed using the PubMed database from 1997 to 2019. Of 179 included patients, 89 underwent revision to RYGB; 52 to sleeve gastrectomy (SG); 32 reversal to original anatomy; and 6 underwent partial revision with gastro-gastrostomy alone. Most common indications were severe malnutrition, chronic bile reflux, intractable marginal ulcerations, and insufficient weight loss. Postoperative complication rates ranged from 5 to 35%.

Short- and intermediate-term clinical outcome comparison between laparoscopic and robotic-assisted median arcuate ligament release.

While laparoscopic median arcuate ligament (MAL) release remains the most common approach, robotic-assisted MAL release has been increasingly performed by several institutions. This study aims to compare surgical outcomes between laparoscopic and robotic-assisted MAL release. This is a retrospective study of patients undergoing laparoscopic and robotic-assisted MAL release in a teaching hospital from January 1999 to December 2018. Intraoperative and postoperative outcomes as well as short- and intermediate-term clinical outcomes were compared between the two groups. A total of 16 laparoscopic and 18 robotic cases were included. Demographics and baseline characteristics were similar between the two comparison groups. Median operative time was shorter in the robotic group [179.5 (IQR 127.3-225) vs. 106 (IQR 80.8-122.8) minutes; p < 0.001]. The rates of conversion to open operation were similar in both groups (6.3% vs. 5.6%, p = 0.99). Conversions to laparotomy were performed due to bleeding and extensive adhesions in one laparoscopic case and due to technical difficulties in a patient with narrow body habitus in the robotic group. Postoperative complication rates were similar (12.5% vs. 16.7%, p = 0.99), all in grade I and II. Complete pain resolution rates (37.5% vs. 44.4%, p = 0.93), symptom recurrence rates (37.5% vs. 27.8%, p = 0.93), and overall clinical improvement at last follow-up (87.5% vs. 77.8%, p = 0.66) were not statistically different. Both laparoscopic and robotic-assisted MAL release offer similar short- and intermediate-term clinical outcomes. A shortened operative time may be achieved by incorporating the robot platform.

Factors Associated with Symptomology of Celiac Artery Compression and Outcomes following Median Arcuate Ligament Release.

BACKGROUND: This study aims to identify potential risk factors for becoming symptomatic in patients with radiographic celiac artery compression (CAC) as well as prognostic factors for patients with median arcuate ligament syndrome (MALS) who underwent surgical ligament release. METHODS: This is a retrospective cohort study of patients with findings of CAC on computed tomography or magnetic resonance angiography (CT/MRA) who were asymptomatic and who were diagnosed with MALS at a single university hospital between January 2001 and 2018. RESULTS: Following a review of 1,330 CT/MRA reports, a total of 109 patients were identified as having radiographically apparent CAC. Among these, 48 (44.0%) patients were symptomatic. Univariate comparison between those with and without symptoms showed that symptomatic patients were more commonly younger than 30 years old [17/48 (35.4%) vs. 8/61 (13.1%), P = 0.006], had a history of prior abdominal surgery [25/48 (52.1%) vs. 18/61 (29.5%), P = 0.017], and had high-grade stenosis [32/43 (74.4%) vs. 25/61 (41.0%), P = 0.001]. Among 41 included patients who underwent surgical release of the median arcuate ligament including open, laparoscopic, and robotic approaches, 82.9% reported overall clinical improvement, 5/41 (12.2%) reported persistent pain, and 13/36 (36.0%) experienced pain recurrence. The only identified risk factor associated with symptom recurrence was American Society of Anesthesiologists class III [7/13 (53.8%) vs. 4/23 (17.4%), P = 0.029]. CONCLUSIONS: The severity of stenosis and prior abdominal surgery both contributed to symptom development in patients with radiographically apparent CAC from the median arcuate ligament.

Percutaneous cholecystostomy for grade III acute cholecystitis is associated with worse outcomes.

BACKGROUND: The aim of the present study was to evaluate the mortality, morbidity, and readmissions associated with management of grade 3 cholecystitis in the elderly, vulnerable population. METHODS: This was a retrospective cohort study of non-elective admissions for acute cholecystitis from 2010 to 2015 using the nationwide readmissions database for adults ≥ 65 years with evidence of end-organ dysfunction (grade 3) who underwent percutaneous cholecystostomy (PC), laparoscopic (LC) or open cholecystectomy (OC). Index and readmission outcomes were analyzed using logistic regression and inverse probability treatment weight analysis. RESULTS: Of the estimated 358,624 patients, 14.9% underwent PC, 15.7% OC, and 69.4% LC. PC had significantly higher odds of mortality (AOR 5.8, 95%CI 5.1-6.6), composite morbidity (AOR 3.8, 95%CI 3.5-4.1), early (AOR 1.9, 95%CI 1.7-2.0) and intermediate (AOR 2.2, 95%CI 2.0-2.5) readmission compared to LC and OC. CONCLUSIONS: Patients undergoing cholecystostomy had higher mortality, complications, and readmission rates warranting revaluation of criteria for cholecystostomy at initial presentation.

Trends in Diverting Loop Ileostomy vs Total Abdominal Colectomy as Surgical Management for Clostridium difficile Colitis.

Importance: Diverting loop ileostomy and colonic lavage has generated much interest since it was first reported as a potential alternative to total abdominal colectomy for treating Clostridium difficile colitis in 2011. To our knowledge, few studies have validated the benefit reported in the initial description, and the association of this new approach with practice patterns has not been described. Objective: To examine the national adoption pattern and outcomes of diverting loop ileostomy vs total abdominal colectomy as treatment for fulminant C difficile colitis. Design, Setting, and Participants: This retrospective cohort study used data from hospitals participating in the National Inpatient Sample database across the United States from January 2011 to September 2015 and included 3021 adult patients who underwent surgery for C difficile colitis during the study period, comprising 2408 subtotal colectomies and 613 loop ileostomies. The data were analyzed between November 2018 and April 2019. Exposures: Loop ileostomy as surgery of choice. Main Outcomes and Measures: In-hospital mortality. Results: Of 2408 participants, 1416 (58.8%) were women, 1781 (78.4%) were white, and 627 (21.6%) were individuals of color and the mean (SD) age was 68.2 (14.8) years. During the overall study period, 613 patients (20.28%) underwent diverting loop ileostomy without total abdominal colectomy. The annual proportion of patients undergoing only diversion increased from 11.16% in 2011 to 25.30% in 2015. Significantly more loop ileostomies were performed within the first day of hospitalization, in contrast to subtotal colectomies (23.31% vs 12.21%; P < .01). There was no significant difference in in-hospital mortality rates between the 2 groups (25.98% vs 31.18%; P = .28). Conclusions and Relevance: This study demonstrates the adoption of diverting loop ileostomy to treat C difficile colitis across the United States. While fulminant C difficile colitis remains a condition with high mortality rates, no significant difference in this outcome was observed between loop ileostomy and total abdominal colectomy. Loop ileostomy may represent a viable surgical alternative to total abdominal colectomy, although the grounds for selection of treatment need to be clarified.

Trends in Readmission and Costs After Transcatheter Implantation Versus Surgical Aortic Valve Replacement in Patients With Renal Dysfunction.

Patients with renal dysfunction are at increased risk for developing aortic valve pathology. In the present era of value-based healthcare delivery, a comparison of transcatheter and surgical aortic valve replacement (SAVR) readmission performance in this population is warranted. All adult patients who underwent transcatheter or SAVR from 2011 to 2014 were identified using the Nationwide Readmissions Database, containing data for nearly 50% of US hospitalizations. Patients were further stratified as chronic kidney disease stage 1 to 5 as well as end-stage renal disease requiring dialysis. Kaplan-Meier, Cox Hazard, and multivariable regression models were generated to identify predictors of readmission and costs. Of the 350,609 isolated aortic valve replacements, 4.7% of patients suffered from chronic kidney disease stages 1 to 5 or end-stage renal disease. Transcatheter aortic valve patients with chronic kidney disease stages 1 to 5/or end-stage renal disease were older (81.9 vs 72.9 years, p <0.0001) with a higher prevalence of heart failure (15.2 vs 4.3%, p = 0.04), and peripheral vascular disease (31.1 vs 22.8%, p <0.0001) compared to their SAVR counterparts. Transcatheter aortic valve replacement in chronic kidney disease stage 1 to 3 patients had a higher rate of readmission due to heart failure and pacemaker placement than SAVR. Transcatheter aortic valve replacement was associated with increased costs compared with SAVR for all renal failure patients. In conclusion, in this national cohort of chronic and end-stage renal disease patients, transcatheter aortic valve implantation was associated with increased mortality, readmissions for chronic kidney disease stages1 to 3, and index hospitalization costs.

Multi-Modal Haptic Feedback for Grip Force Reduction in Robotic Surgery.

Minimally invasive robotic surgery allows for many advantages over traditional surgical procedures, but the loss of force feedback combined with a potential for strong grasping forces can result in excessive tissue damage. Single modality haptic feedback systems have been designed and tested in an attempt to diminish grasping forces, but the results still fall short of natural performance. A multi-modal pneumatic feedback system was designed to allow for tactile, kinesthetic, and vibrotactile feedback, with the aims of more closely imitating natural touch and further improving the effectiveness of HFS in robotic surgical applications and tasks such as tissue grasping and manipulation. Testing of the multi-modal system yielded very promising results with an average force reduction of nearly 50% between the no feedback and hybrid (tactile and kinesthetic) trials (p < 1.0E-16). The multi-modal system demonstrated an increased reduction over single modality feedback solutions and indicated that the system can help users achieve average grip forces closer to those normally possible with the human hand.

Impact of Approach and Hospital Volume on Cardiovascular Complications After Pulmonary Lobectomy.

BACKGROUND: Cardiovascular complications contribute significantly to the morbidity and resource utilization after pulmonary resections. Maturation of less-invasive technologies, such as video and robot-assisted thoracoscopic surgery, aims at improving postoperative outcomes by reducing the trauma of surgery. The present work aimed to evaluate changes in cardiovascular complications after open and minimally invasive lobectomies in the United States. METHODS: We performed a retrospective analysis of the Nationwide Inpatient Sample for patients having elective open, video-assisted, and robot-assisted thoracoscopic lobectomy during 2008-2014. Logistic regression was performed to determine predictors of in-hospital mortality, myocardial infarction (MI), cardiac arrest (CA), and postoperative pulmonary embolism (PE). RESULTS: A total of 201,226 patients underwent pulmonary lobectomy over the study period. Open thoracotomy (OPEN) approach has steadily decreased from 75%-52% (P < 0.0001), whereas minimally invasive surgery (MIS) utilization has increased from 25%-48% (P < 0.0001) of all lobectomies. MIS approach was independently associated with decreased odds of mortality (odds ratio [OR] 0.6, 95% confidence interval [CI] 0.50-0.73) and PE (OR 0.67, 95% CI 0.50-0.91). MIS patients at high volume institutions had the lowest odds of all-cause mortality (OR 0.27, 95% CI 0.26-0.53) and MI (OR 0.57, 95% CI 0.38-0.87). Operative approach and institutional lobectomy caseload reduced odds of mortality after MI, CA, or PE. Overall, the incidence of MI, CA, and PE increased. CONCLUSIONS: MIS lobectomies increased without a concurrent reduction in perioperative MI, CA, or PE incidence. High hospital lobectomy volume and MIS approach decrease odds of failure to rescue. Improved perioperative management of cardiovascular risk is warranted to reduce the morbidity, mortality, and resource utilization associated with these complications.

Care fragmentation is associated with increased short-term mortality during postoperative readmissions: A systematic review and meta-analysis.

BACKGROUND: Recent trends toward regionalization of complex surgical procedures may increase the risk for care fragmentation during readmissions. Conflicting conclusions have been reported regarding risk factors and consequences of nonindex readmissions (ie, readmission to a separate hospital than the one where surgery was originally performed). We seek to perform a comprehensive review of existing literature. METHODS: Four electronic databases were searched to identify all eligible studies examining the risk factors and outcomes of postoperative nonindex readmission. The pooled odds ratio and 95% confidence interval were calculated using a random-effects model. RESULTS: A total of 444 studies were retrieved from database searches and 23 were included after applying eligibility criteria. Nonindex readmissions constituted 10%-47% of 30-day readmissions. Risk factors for nonindex readmission predominantly represented proxy variables for patient care access that may not be modifiable, such as residing in a location further away from the original hospital, being older in age, living in rural areas, and having lower income. Nonindex readmissions occurred more commonly under urgent conditions. Ten of the 14 studies that employed short-term mortality as the primary outcome concluded that nonindex readmissions were significantly associated with higher mortality after adjusting for available confounders. CONCLUSION: The findings of the current study suggest that nonindex readmission is a common phenomenon after surgery and is associated with increased mortality. Further studies are required to evaluate whether enhancing health information continuity between hospitals would be helpful for mitigating the adverse consequences of care fragmentation.

Complete Impact of Care Fragmentation on Readmissions Following Urgent Abdominal Operations.

BACKGROUND: Urgent abdominal operations commonly occurred in low-volume hospitals with high failure-to-rescue rates. Recent studies have demonstrated a survival benefit associated with readmission to the original hospital after operation, presumably due to improved continuity of care. It is unclear if this survival benefit persists in low-volume hospitals. We seek to evaluate differences in mortality between readmission to the original hospital and a higher-volume hospital after urgent abdominal operations. METHODS: A retrospective cohort study using the National Readmissions Database from 2010 to 2014 was performed. Propensity score-weighted multilevel regression analysis was used to examine the association between readmission destination and mortality after accounting for hospital volume. RESULTS: A total of 71,551 adult patients who experienced 30-day readmission following urgent abdominal operations were identified, among whom 10,368 (14.5%) were readmitted to a different hospital. Patients with higher baseline comorbidity scores, lower income, less comprehensive insurance coverage, systemic complications, prolonged length of stay, or non-home disposition were more likely to experience readmission to a different hospital. Following stratification by readmission hospital volume and propensity score weighting to adjust for baseline mortality risk differences, readmission to a different hospital is still associated with higher mortality rates than the original hospital. CONCLUSIONS: The adverse outcomes associated with case fragmentation are present even after adjusting for readmission hospital volume. Patients who received urgent abdominal operations at low-volume hospitals should return to the original hospital for concern of care fragmentation.

Application of a newly designed microfork probe for robotic-guided pelvic intraoperative neuromapping.

Introduction: Robotic-assisted total mesorectal excision (TME) with pelvic intraoperative neuromapping was recently accomplished. However, neuromapping is conventionally conducted by a hand-guided laparoscopic probe. We introduce a prototype microfork probe to make robotic-guided neuromapping feasible. Experiments and Technical Setup: Two porcine experiments with nerve-sparing TME surgery were performed. A newly designed prototype bipolar microfork probe was inserted intraabdominally and guided with the robotic forceps. Intermittent neuromapping was then conducted and neuromonitoring data integrated in the surgeon console viewer. Conclusion: Robotic-guided neuromapping is shown to be feasible and fully controllable from the surgeon console.

An Innovative Approach for Familiarizing Surgeons with Malpractice Litigation.

OBJECTIVE: Familiarize surgery residents with medicolegal knowledge and skills required when facing the prospect of being sued through a simulation session. DESIGN: The general surgery residency, hospital risk management, and malpractice attorneys collaboratively organized an educational intervention, consisting of an introductory lecture followed by a mock lawsuit. Two medical malpractice attorneys acted as defense and plaintiff attorneys while an attending surgeon experienced in litigation acted as defendant. Experience, attitudes, and preintervention/postintervention competency were evaluated via retrospective self-assessment. SETTING: Weekly departmental educational conference. PARTICIPANTS: Forty residents and attending surgeons. RESULTS: Among the participants, 27.5% had been named in a law suit before. Most surgeons (70.0%) are worried about malpractice. Physicians who had been sued were no more likely to worry about malpractice (18.6 vs 25.0%, p = 0.82) than their colleagues who had never been sued. Results from the retrospective preintervention/postintervention competency assessments demonstrated significant improvement in all measured competencies after the mock lawsuit. In comparison with attending faculty, residents obtained greater improvements in understanding the essential elements of a medical claim (1.9 vs 1.1, p = 0.03), gaining confidence doing a deposition for medical litigation (1.9 vs 0.9, p < 0.01) and understanding the do's and don'ts when named in a lawsuit (2.0 vs 1.1, p = 0.01). CONCLUSIONS: The novel educational format effectively familiarized surgery faculty and residents with the process of litigation and improved their confidence and mental preparedness when facing the prospect of a lawsuit. It is a valuable educational tool that can be incorporated in residency training and faculty development curricula.

Characterization of perfused and sectioned liver tissue in a full indentation cycle using a visco-hyperelastic model.

Realistic modeling of biologic material is required for optimizing fidelity in computer-aided surgical training and assistance systems. The modeling of liver tissue has remained challenging due to its nonlinear viscoelastic properties and high hysteresis of the stress-strain relation. While prior studies have described the behavior of liver tissue during the loading status (in elongation, compression, or indentation tests) or unloading status (in stress relaxation or creep tests), a hysteresis curve with both loading and unloading processes was incompletely defined. We seek to use a single material model to characterize the mechanical properties of liver tissue in a full indentation cycle ex vivo perfused and then sectioned. Based on measurements taken from ex-vivo perfused porcine livers, we converted force-displacement curves to stress-strain curves and developed a visco-hyperelastic constitutive model to characterize the liver's mechanical behavior at different locations under various rates of indentation (1, 2, 5, 10, and 20 mm/s). The proposed model is a mixed visco-hyperelastic model with up to 6 coefficients. The normalized root mean square standard deviations of fitted curves are less than 5% and 10% in low (<0.05) and high strain (>0.3) conditions respectively.