A predictive Bayesian network that risk stratifies patients undergoing Barrett's surveillance for personalized risk of developing malignancy.

BACKGROUND: Barrett's esophagus is strongly associated with esophageal adenocarcinoma. Considering costs and risks associated with invasive surveillance endoscopies better methods of risk stratification are required to assist decision-making and move toward more personalised tailoring of Barrett's surveillance. METHODS: A Bayesian network was created by synthesizing data from published studies analysing risk factors for developing adenocarcinoma in Barrett's oesophagus through a two-stage weighting process. RESULTS: Data was synthesized from 114 studies (n = 394,827) to create the Bayesian network, which was validated against a prospectively maintained institutional database (n = 571). Version 1 contained 10 variables (dysplasia, gender, age, Barrett's segment length, statin use, proton pump inhibitor use, BMI, smoking, aspirin and NSAID use) and achieved AUC of 0.61. Version 2 contained 4 variables with the strongest evidence of association with the development of adenocarcinoma in Barrett's (dysplasia, gender, age, Barrett's segment length) and achieved an AUC 0.90. CONCLUSION: This Bayesian network is unique in the way it utilizes published data to translate the existing empirical evidence surrounding the risk of developing adenocarcinoma in Barrett's esophagus to make personalized risk predictions. Further work is required but this tool marks a vital step towards delivering a more personalized approach to Barrett's surveillance.

Decision analysis of minimally invasive management options for cholecysto-choledocholithiasis.

BACKGROUND: The management of cholecysto-choledocholithiasis is controversial with the risks and benefits of one versus two-stage approaches debated. This study aims to perform decision analysis of minimally invasive laparo-endoscopic approaches. METHODS: An advanced decision tree was constructed to compare pre, intra and post-operative ERCP and laparoscopic common bile duct exploration in terms of primary ductal clearance and significant complications for patients intended to undergo laparoscopic cholecystectomy. Transition probabilities were calculated from randomised controlled trials following a comprehensive literature search. Model uncertainties were extensively tested through deterministic and probabilistic Monte Carlo sensitivity analysis. Utility outcomes were 1 and 0.5 for successful primary clearance without and with complications, respectively, and 0 for failure of primary clearance of the duct. RESULTS: Twenty-one studies (n = 2697) were included in the analysis. At base case analysis, a laparo-endoscopic rendezvous approach had the highest utility output (0.90; no complication probability: 0.87/complication probability 0.06). Laparoscopic common bile duct exploration was ranked second with a utility output 0.87 (no complication probability: 0.82/complication probability 0.10). Pre-operative ERCP utility score was 0.84 (no complication probability: 0.78/ complication probability 0.11) and post-operative ERCP utility score was 0.78 (no complication probability: 0.71/complication probability 0.13). Monte Carlo analysis showed that laparo-endoscopic rendezvous and laparoscopic common bile duct exploration had an equal mean utility output of 0.57 (standard deviation 0.36; variance 0.13; 95% confidence interval 0.00-0.99 versus standard deviation 0.34; variance 0.12; 95% confidence interval 0.01-0.98). Laparo-endoscopic rendezvous had a superior treatment selection frequency of 39.93% followed by laparoscopic bile duct exploration (36.11%), pre-operative ERCP (20.67%) and post-operative ERCP (2.99%). CONCLUSION: One-stage approach to the management of cholecysto-choledocholithiasis is superior to two-stage, in terms of primary clearance of the duct and risk of operative morbidity. Laparo-endoscopic rendezvous approach could offer marginal additional benefit but more high-quality randomised controlled trials are needed.

A prognostic Bayesian network that makes personalized predictions of poor prognostic outcome post resection of pancreatic ductal adenocarcinoma.

BACKGROUND: The narrative surrounding the management of potentially resectable pancreatic cancer is complex. Surgical resection is the only potentially curative treatment. However resection rates are low, the risk of operative morbidity and mortality are high, and survival outcomes remain poor. The aim of this study was to create a prognostic Bayesian network that pre-operatively makes personalized predictions of post-resection survival time of 12months or less and also performs post-operative prognostic updating. METHODS: A Bayesian network was created by synthesizing data from PubMed post-resection survival analysis studies through a two-stage weighting process. Input variables included: inflammatory markers, tumour factors, tumour markers, patient factors and, if applicable, response to neoadjuvant treatment for pre-operative predictions. Prognostic updating was performed by inclusion of post-operative input variables including: pathology results and adjuvant therapy. RESULTS: 77 studies (n = 31,214) were used to create the Bayesian network, which was validated against a prospectively maintained tertiary referral centre database (n = 387). For pre-operative predictions an Area Under the Curve (AUC) of 0.7 (P value: 0.001; 95% CI 0.589-0.801) was achieved accepting up to 4 missing data-points in the dataset. For prognostic updating an AUC 0.8 (P value: 0.000; 95% CI:0.710-0.870) was achieved when validated against a dataset with up to 6 missing pre-operative, and 0 missing post-operative data-points. This dropped to AUC: 0.7 (P value: 0.000; 95% CI:0.667-0.818) when the post-operative validation dataset had up to 2 missing data-points. CONCLUSION: This Bayesian network is currently unique in the way it utilizes PubMed and patient level data to translate the existing empirical evidence surrounding potentially resectable pancreatic cancer to make personalized prognostic predictions. We believe such a tool is vital in facilitating better shared decision-making in clinical practice and could be further developed to offer a vehicle for delivering personalized precision medicine in the future.

A systematic review of methodological quality of model development studies predicting prognostic outcome for resectable pancreatic cancer.

OBJECTIVES: To assess the methodological quality of prognostic model development studies pertaining to post resection prognosis of pancreatic ductal adenocarcinoma (PDAC). DESIGN/SETTING: A narrative systematic review of international peer reviewed journals DATA SOURCE: Searches were conducted of: MEDLINE, Embase, PubMed, Cochrane database and Google Scholar for predictive modelling studies applied to the outcome of prognosis for patients with PDAC post resection. Predictive modelling studies in this context included prediction model development studies with and without external validation and external validation studies with model updating. Data was extracted following the Checklist for critical Appraisal and data extraction for systematic Reviews of prediction Modelling Studies (CHARMS) checklist. PRIMARY AND SECONDARY OUTCOME MEASURES: Primary outcomes were all components of the CHARMS checklist. Secondary outcomes included frequency of variables included across predictive models. RESULTS: 263 studies underwent full text review. 15 studies met the inclusion criteria. 3 studies underwent external validation. Multivariable Cox proportional hazard regression was the most commonly employed modelling method (n=13). 10 studies were based on single centre databases. Five used prospective databases, seven used retrospective databases and three used cancer data registry. The mean number of candidate predictors was 19.47 (range 7 to 50). The most commonly included variables were tumour grade (n=9), age (n=8), tumour stage (n=7) and tumour size (n=5). Mean sample size was 1367 (range 50 to 6400). 5 studies reached statistical power. None of the studies reported blinding of outcome measurement for predictor values. The most common form of presentation was nomograms (n=5) and prognostic scores (n=5) followed by prognostic calculators (n=3) and prognostic index (n=2). CONCLUSIONS: Areas for improvement in future predictive model development have been highlighted relating to: general aspects of model development and reporting, applicability of models and sources of bias. TRIAL REGISTRATION NUMBER: CRD42018105942.

Personalized Pancreatic Cancer Management: A Systematic Review of How Machine Learning Is Supporting Decision-making.

This review critically analyzes how machine learning is being used to support clinical decision-making in the management of potentially resectable pancreatic cancer. Following PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) guidelines, electronic searches of MEDLINE, Embase, PubMed, and Cochrane Database were undertaken. Studies were assessed using the checklist for critical appraisal and data extraction for systematic reviews of prediction modeling studies (CHARMS) checklist. In total 89,959 citations were retrieved. Six studies met the inclusion criteria. Three studies were Markov decision-analysis models comparing neoadjuvant therapy versus upfront surgery. Three studies predicted survival time using Bayesian modeling (n = 1) and artificial neural network (n = 1), and one study explored machine learning algorithms including Bayesian network, decision trees, k-nearest neighbor, and artificial neural networks. The main methodological issues identified were limited data sources, which limits generalizability and potentiates bias; lack of external validation; and the need for transparency in methods of internal validation, consecutive sampling, and selection of candidate predictors. The future direction of research relies on expanding our view of the multidisciplinary team to include professionals from computing and data science with algorithms developed in conjunction with clinicians and viewed as aids, not replacement, to traditional clinical decision-making.

Neoadjuvant therapy versus upfront surgery for potentially resectable pancreatic cancer: A Markov decision analysis.

BACKGROUND: Neoadjuvant therapy has emerged as an alternative treatment strategy for potentially resectable pancreatic cancer. In the absence of large randomized controlled trials offering a direct comparison, this study aims to use Markov decision analysis to compare efficacy of traditional surgery first (SF) and neoadjuvant treatment (NAT) pathways for potentially resectable pancreatic cancer. METHODS: An advanced Markov decision analysis model was constructed to compare SF and NAT pathways for potentially resectable pancreatic cancer. Transition probabilities were calculated from randomized control and Phase II/III trials after comprehensive literature search. Utility outcomes were measured in overall and quality-adjusted life months (QALMs) on an intention-to-treat basis as the primary outcome. Markov cohort analysis of treatment received was the secondary outcome. Model uncertainties were tested with one and two-way deterministic and probabilistic Monte Carlo sensitivity analysis. RESULTS: SF gave 23.72 months (18.51 QALMs) versus 20.22 months (16.26 QALMs). Markov Cohort Analysis showed that where all treatment modalities were received NAT gave 35.05 months (29.87 QALMs) versus 30.96 months (24.86QALMs) for R0 resection and 34.08 months (29.87 QALMs) versus 25.85 months (20.72 QALMs) for R1 resection. One-way deterministic sensitivity analysis showed that NAT was superior if the resection rate was greater than 51.04% or below 75.68% in SF pathway. Two-way sensitivity analysis showed that pathway superiority depended on obtaining multimodal treatment in either pathway. CONCLUSION: Whilst NAT is a viable alternative to traditional SF approach, superior pathway selection depends on the individual patient's likelihood of receiving multimodal treatment in either pathway.

Upfront Surgery versus Neoadjuvant Therapy for Resectable Pancreatic Cancer: Systematic Review and Bayesian Network Meta-analysis.

Current treatment recommendations for resectable pancreatic cancer support upfront resection and adjuvant therapy. Randomized controlled trials offering comparison with the emerging neoadjuvant approach are lacking. This review aims to compare both treatment strategies for resectable pancreatic cancer. PubMed, MEDLINE, Embase, Cochrane Database and Cochrane Databases were searched for studies comparing neoadjuvant and surgery-first with adjuvant therapy for resectable pancreatic cancer. A Bayesian network meta-analysis was conducted using the Markov chain Monte Carlo method. Cochrane Collaboration's risk of bias, ROBINS-I and GRADE tools were used to assess quality and risk of bias of included trials. 9 studies compared neoadjuvant therapy and surgery-first with adjuvant therapy (n = 22,285). Aggregate rate (AR) of R0 resection for neoadjuvant therapy was 0.8008 (0.3636-0.9144) versus 0.7515 (0.2026-0.8611) odds ratio (O.R.) 1.27 (95% CI 0.60-1.96). 1-year survival AR for neoadjuvant therapy was 0.7969 (0.6061-0.9500) versus 0.7481 (0.4848-0.8500) O.R. 1.38 (95% CI 0.69-2.96). 2-year survival AR for neoadjuvant therapy was 0.5178 (0.3000-0.5970) versus 0.5131 (0.2727-0.5346) O.R. 1.26 (95% CI 0.94-1.74). 5-year AR survival for neoadjuvant therapy was 0.2069 (0.0323-0.3300) versus 0.1783 (0.0606-0.2300) O.R. 1.19 (95% CI 0.65-1.73). In conclusion neoadjuvant therapy may offer benefit over surgery-first and adjuvant therapy. However, further randomized controlled trials are needed.

Health Care Discrimination, Sex Behavior Disclosure, and Awareness of Pre-Exposure Prophylaxis Among Black Men Who Have Sex With Men.

BACKGROUND: Perceived healthcare-related discrimination and disclosure of same-sex sex behaviors to healthcare providers may act as barriers to awareness of pre-exposure prophylaxis (PrEP) for Black/African-American men who have sex with men (BMSM). Given the elevated rates of HIV transmission among young BMSM in particular, age is likely an important factor for determining the correlates of PrEP awareness unique to BMSM of different ages. METHOD: 147 BMSM (M age = 30.6 years, SD = 10.3 years) located in the Southeastern United States were recruited from gay-identified bars, clubs, bathhouses, parks, and street locations, via online classifieds (e.g., Craigslist) and social media (e.g., Facebook). Participants completed surveys that included questions about demographic characteristics, perceived healthcare-related discrimination, disclosure of same-sex sex behavior to healthcare providers, and PrEP awareness. RESULTS: Perceived healthcare-related discrimination was significantly, negatively associated with PrEP awareness, and same-sex sex behavior disclosure to healthcare providers was significantly, positively related to awareness of PrEP among BMSM. A moderation analysis, with participant age as the moderator, revealed that higher perceived healthcare-related discrimination was significantly, negatively associated with PrEP awareness beginning at 30.2 years of age, and that the relationship strengthened as age increased. DISCUSSION: Perceived healthcare-related discrimination plays a particularly important role in PrEP awareness for BMSM who are 30 years of age and older. Discrimination in healthcare settings may impact BMSM's ability, particularly those who are older, to access PrEP information. Healthcare professionals must establish procedures for identifying appropriate patients for PrEP, and prioritize addressing the psychosocial factors that impede PrEP awareness for their BMSM patients.

Sexual Health, Mental Health, and Beliefs About Cancer Treatments Among Women Attending a Gynecologic Oncology Clinic.

INTRODUCTION: Sexual health is an important, yet overlooked, aspect of quality of life for gynecologic oncologic patients. Although patients with gynecologic cancer frequently report sexual health concerns, there are limited efforts to address these problems. A comprehensive understanding of the relationship between mental health and sexual health needs to be prioritized. AIM: To examine multiple components of sexual health in patients with gynecologic cancer. METHODS: For the present study, sexual health concerns (ie, sexual frequency, desire, response, and satisfaction; orgasm; and pain during sex; independent variables), beliefs about cancer treatments affecting sexual health (dependent variable), and mental health (ie, anxiety and depressive symptoms; dependent variables) of patients at a US gynecologic oncology clinic were assessed. MAIN OUTCOME MEASURES: Demographics; cancer diagnosis; positive screening results for cancer; sexual health histories including sexual frequency, desire, pain, orgasm, responsiveness, and satisfaction; and mental health including depression and anxiety symptoms. RESULTS: Most women reported experiencing at least one sexual health concern, and half the women screened positive for experiencing symptoms of depression and anxiety. Forty-nine percent of participants reported having no or very little sexual desire or interest in the past 6 months. Further, in mediation analyses, pain during sex was significantly and positively correlated with depressive symptoms (r = 0.42, P < .001), and this relationship was fully mediated by believing that cancer treatments affected one's sexual health (B = 0.16, 95% confidence interval = 0.01-0.48, P < .05). CONCLUSION: Findings emphasize the need to further address and incorporate sexual and mental health into standard care for patients attending gynecologic oncology clinics. Screening women for whether and to what extent they perceive cancer treatments affecting their sexual health could provide a brief, easily administrable, screener for sexual health concerns and the need for further intervention. Intervention development for patients with gynecologic cancer must include mental health components and addressing perceptions of how cancer treatments affect sexual health functioning. Eaton L, Kueck A, Maksut J, et al. Sexual Health, Mental Health, and Beliefs About Cancer Treatments Among Women Attending a Gynecologic Oncology Clinic. Sex Med 2017;5:e175-e183.

Extralevator abdominoperineal excision (Elape): A retrospective cohort study.

INTRODUCTION: Extralevator abdominoperineal excision (ELAPE) is relatively new surgical technique for low rectal cancers. It is a more radical approach than conventional abdominoperineal excision (APE) with potentially better oncological outcome. The aim of this study was to analyse short term results of ELAPE compared with conventional abdominoperineal excision. METHODS: Data were collected prospectively for 72 patients who underwent abdominoperineal excision (APE) for low rectal carcinomas from 2010 to 2014. Of these 24 patients underwent ELAPE with biological prosthetic mesh used to close the perineal defect. RESULTS: The median age of patients was 68 (37-87). Positive circumferential resection margin (1/24 vs. 8/48) and Intra operative perorations (0/24 vs. 6/48) compared favourably with ELAPE. CONCLUSIONS: Short term results from this study support that ELAPE has better oncological outcome.

From cadavers to clinical practice: the anatomy of lifelong learning.

BACKGROUND: Much has been postulated about the perceived deterioration of anatomy knowledge amongst graduates. Little is known about levels of confidence in, and educational needs concerning, clinical anatomy knowledge amongst foundation year doctors. AIMS: To establish foundation year doctors' perceptions of anatomy related to: importance to career, confidence in anatomy knowledge and its application, preferred methods of teaching. Secondarily, to determine impact of an integrated clinical approach to anatomy teaching on foundation year doctors' level of knowledge and confidence in its clinical application of anatomy. METHODS: A course teaching anatomy through common surgeries and related radiology was delivered to foundation year doctors. A pre- and post-course assessment based on anatomy competence score assessed holistic knowledge acquisition. Foundation year doctors' perceptions of anatomy and course satisfaction were measured through questionnaire. RESULTS: Confidence in applying anatomy knowledge was low. The average pre- and post-course assessment score increased from 55% to 81%; 92.86% felt an integrated clinical approach to anatomy teaching improved their confidence on the subject and 58.62% felt it improved their clinical skills. CONCLUSION: This study identified a need for ongoing educational support for foundation year doctors regarding anatomy teaching. An integrated clinical approach to teaching anatomy proved both highly relevant and popular, as well as an effective teaching approach.

Are we meeting current standards in medicines reconciliation? A study in a District General Hospital.

INTRODUCTION: Inadequate medicines reconciliation on admission is often identified as a major cause of patient morbidity, with poor access to patient's regular medications often cited as a barrier to care. In the surgical admission unit of our district general hospital, drug charts are completed by junior doctors who do not have access to the Emergency Care Summary (ECS) thus making it difficult to accurately complete admission drug charts. METHODS: Our initial measurement of all acute surgical admissions revealed that 49% of patients had an accurate medicines reconciliation upon admission, increasing to 75% within 24 hours of admission. It was clear from this data that our current practice needed improvement in order to ensure patient safety. Resultantly the junior medical staff were provided with ECS accounts and teaching to aid the process of medicines reconciliation. RESULTS: Following the introduction of access to ECS and junior doctor education, a further two data cycles were completed. On the first cycle, the number of accurately completed drug charts increased to 62% on admission and 86% at 24 hours. After the second cycle 57% were complete on admission increasing to 84% at 24 hours. CONCLUSION: Our project has shown that by providing junior doctors with medicines reconciliation education and access to patients' pre-admission medications through a nationwide electronic system resulted in a considerable increase in the completion of medicine reconciliation.

Using a simple handover to improve the timing of gentamicin levels.

The aminoglycoside gentamicin is commonly used in many NHS trusts to cover gram negative organisms in intra-abdominal sepsis and sepsis of unknown origin. As a result it often forms an important part of thew "Sepsis 6" protocol on surgical wards. Despite it's effectiveness, the antibiotic is well known to have nephrotoxic and ototoxic side effects, making monitoring of serum levels vital. In Hairmyres Hospital, a busy district general hospital in Lanarkshire, levels are typically taken at six to 14 hour post-dose intervals, with the result guiding further gentamicin dosing. A baseline measurement was performed highlighting that 42.2% of these levels were taken after the 14 hour limit. This was thought to have serious implications for patient's, as levels designed to protect them from side effects whilst maintain g an effective antimicrobial action were not being performed properly. As a result, a "gentamicin handover" was introduced to the wards in order to ease the workload on junior staff and improve handover between teams. During our short project the number of late levels initially dropped to 33.3% after one week, falling further to 28.6% following the second week of intervention. From our results it is clear that while more intervention is required gentamicin prescription, this project highlights how a simple intervention to improve ward handover can create a very noticeable improvement in the quality of patient care within a small time period.

Unseen but present danger: improving the safe prescribing of anti-embolism stockings (AES).

A strong evidence base exists supporting thromboprophylaxis for venous thromboembolism (VTE) in surgical patients. Given the ageing population, obesity epidemic, and rise in type 2 diabetes, VTE and peripheral vascular disease (PAD) are likely to become an escalating problem. PAD is a contraindication to the use of anti-embolism stockings (AES). Half of those patients diagnosed with PAD report no symptoms, potentially underestimating its prevalence. Implementation of guidelines for thromboprophylaxis, including the safe prescribing of AES, is therefore imperative. The aims of this project were to establish whether thromboprophylaxis was being prescribed correctly, and appropriately, to all surgical inpatients. This included documented evidence that peripheral pulses had been examined - and, in the case of diabetic patients, that there was documentation of full peripheral neurovascular examination - before AES were prescribed. Data were collected from case notes of all surgical inpatients. Foundation year 1 doctors (FY1s) completed a questionnaire assessing their knowledge of local guidelines. Teaching sessions and posters summarising local guidelines were delivered to FY1s. Appropriate pharmacological prescribing improved from 57.69% to 100%. AES were appropriately prescribed for 65.38% of patients. Post intervention this increased to 79.17%. 0% had documented peripheral neurovascular examination. This increased to 50% post intervention.

Improving the quality of patient handover on a surgical ward.

The European Working Time Directive means safe patient hand over is imperative. It is the responsibility of every doctor and an issue of patient safety and clinical governance [1]. The aims of this project were to improve the quality of patient handover between combined assessment unit (CAU) and surgical ward FY1 doctors. The Royal College of Surgeons England (RCSEng) guidelines on surgical patient handover [1] were used as the standard. Data was collected throughout November 2013. A handover tool was then introduced and attached to the front of patient notes when a patient was transferred from CAU to the surgical ward. The doctor handing over the patient and the ward doctor receiving the handover signed this document. Policy was also changed so that handover should take place once the patient had received senior review on the CAU and was deemed appropriate for transfer to the surgical ward. Data from the handover tool was collated and checked against the list of surgical admission for February 2014. The number of patients handed over improved from 15 % to 45%. The quality of patient handover also improved. 0 patient handovers in November 2013 included all of the information recommended by the RCSEng guidelines. 100% of the patient handovers in February 2014 contained all the recommended information. Introduction of a handover tool and formalisation of timing of patient handover helped to improve quality and number of patients being handed over. Further work needs to be done to improve safe handover of surgical patients, particularly out of hours.

How creation of a parent satisfaction questionnaire improved multidisciplinary service delivery in a paediatric day surgery unit.

Auditing patient satisfaction has become a keystone of quality patient centred healthcare. A plethora of patient satisfaction studies exist but only a few studies have been evaluated for their validity, reliability, specificity or psychometric properties. And the majority focus on adult health care. However, if validated tools are not utilised, then inaccurate results could stymie service improvement. The level of satisfaction with the paediatric day surgery service at Tayside Children's Hospital was unknown. Our objective was to measure parent satisfaction with the paediatric day surgery by creating a parent satisfaction questionnaire which has undergone satisfactory testing for validity, reliability, specificity and psychometric properties. A Likert-style questionnaire was constructed through literature review and focus group meetings with professionals, parents and patient groups to establish content validity. Statements worded in positive phrasing were re-worded in negative phrasing to ensure intra-rater reliability. A pilot study was conducted and responses analysed for construct validity and inter-rater agreement. Internal reliability was established using Chronbach's alpha analysis, which produced scores for each part of the questionnaire between 0.7 and 0.9. Overall parent satisfaction was high. 95.48% either strongly agreed or agreed with positively worded statements regarding pre-operative clinic service. In particular 100% satisfaction was reported with the pre-operative phone call which only 70% of participants received. 96.60% strongly agreed or agreed with positive statements regarding service provided on the ward and 87.50% strongly agreed or agreed with positive statements regarding the discharge process. 5% specifically requested improved information giving. In conclusion the parent satisfaction questionnaire was found to have proven validity, reliability, specificity and psychometric properties. Overall parent satisfaction was found to be high. Areas identified for improvement included delivering pre-operative phone call to all parents who have children undergoing day surgery and further exploration of sources and methods of information giving.

Formation of a stable RuvA protein double tetramer is required for efficient branch migration in vitro and for replication fork reversal in vivo.

In bacteria, RuvABC is required for the resolution of Holliday junctions (HJ) made during homologous recombination. The RuvAB complex catalyzes HJ branch migration and replication fork reversal (RFR). During RFR, a stalled fork is reversed to form a HJ adjacent to a DNA double strand end, a reaction that requires RuvAB in certain Escherichia coli replication mutants. The exact structure of active RuvAB complexes remains elusive as it is still unknown whether one or two tetramers of RuvA support RuvB during branch migration and during RFR. We designed an E. coli RuvA mutant, RuvA2(KaP), specifically impaired for RuvA tetramer-tetramer interactions. As expected, the mutant protein is impaired for complex II (two tetramers) formation on HJs, although the binding efficiency of complex I (a single tetramer) is as wild type. We show that although RuvA complex II formation is required for efficient HJ branch migration in vitro, RuvA2(KaP) is fully active for homologous recombination in vivo. RuvA2(KaP) is also deficient at forming complex II on synthetic replication forks, and the binding affinity of RuvA2(KaP) for forks is decreased compared with wild type. Accordingly, RuvA2(KaP) is inefficient at processing forks in vitro and in vivo. These data indicate that RuvA2(KaP) is a separation-of-function mutant, capable of homologous recombination but impaired for RFR. RuvA2(KaP) is defective for stimulation of RuvB activity and stability of HJ·RuvA·RuvB tripartite complexes. This work demonstrates that the need for RuvA tetramer-tetramer interactions for full RuvAB activity in vitro causes specifically an RFR defect in vivo.