Introduction

Colorectal cancer (CRC) stands as a predominant cause of cancer-related mortality globally, ranking as the third leading cause of cancer-related deaths in both men and women in the United States and the second most common cause of cancer death worldwide [1]. CRC tends to develop more stealthily than other tumors, often lacking specific clinical indicators in its early stages. Consequently, the disease frequently advances to more severe stages by the time of diagnosis, carrying a grim prognosis and commonly presenting symptoms such as alterations in bowel habits, abdominal pain, and hematochezia [2]. Therefore, safe and effective early intervention, including surgical approaches, is critically important for CRC patients. Since the introduction of laparoscopic colectomy in 1991, there has been a gradual increase in patients receiving laparoscopic colorectal surgery, which has emerged as a new standard for treating colorectal diseases [3]. This method offers numerous benefits over traditional open surgery, including reduced hospital stays, quicker recovery to normal functions, diminished postoperative pain, and enhanced cosmetic outcomes [4].

With rising living standards, changes in dietary habits, and a decrease in physical activity, the prevalence of obesity is increasing steadily. This trend has resulted in a growing frequency of surgeries for obese patients with rectal cancer [5]. Nonetheless, laparoscopic colorectal surgery poses particular challenges in obese patients due to significant abdominal fat accumulation, which can obscure the anatomical landmarks during laparoscopic pelvic surgery. This difficulty in visualizing the surgical field and accessing confined spaces can increase the risk of vascular and nerve injuries and may necessitate a conversion to open surgery [6]. Obesity is recognized as a significant risk factor for increased morbidity, higher conversion rates, and greater blood loss during conventional laparoscopic colorectal surgery [7, 8]. Since Pigazzi et al [9]. introduced the first robot-assisted rectal cancer resection in 2006, robotic technology has increasingly been applied in colorectal cancer surgery. Robotic systems offer advantages such as three-dimensional stereoscopic vision, enhanced dexterity, and high-resolution imaging, facilitating delicate tasks, such as suturing, knot-tying, and precise perivascular dissection. This technology provides clearer visualization of pelvic nerves, particularly beneficial in obese patients, where anatomical clarity is compromised, thereby minimizing the risk of iatrogenic damage [10].

Despite the potential benefits of robotic surgery in addressing the technical challenges presented by obesity, there is scant literature comparing its efficacy to that of laparoscopic surgery in obese patients. This paper aims to fill this gap through a systematic review and meta-analysis, evaluating the effectiveness of robotic versus laparoscopic colorectal surgery in this specific patient population.

Literature search

This research adhered rigorously to the PRISMA [11] (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines and was duly registered in the PROSPERO database (CRD42024520593), ensuring a structured and transparent methodology. Two adept researchers independently screened papers and meticulously extracted data based on predefined inclusion and exclusion criteria to ascertain their eligibility for this systematic review. We gathered pertinent literature up to February 1, 2024, employing a thorough search strategy across renowned databases, including MEDLINE, EMBASE, and the Cochrane Library, and restricting our focus to articles published in Chinese and English. Our search utilized Medical Subject Headings (MeSH) alongside keywords such as “colorectal,” “surgery,” “robotics,” and “laparoscopy” to maximize the relevance and breadth of our findings. In addition, we undertook a manual search and reviewed further relevant references to ensure no pertinent study was overlooked, thereby enhancing the robustness and comprehensiveness of our review.

Inclusion and exclusion criteria

This investigation was structured around the PICOS (Population, Intervention, Comparison, Outcomes, Study Type) framework to formulate and address pertinent clinical inquiries. The population (P) targeted includes patients diagnosed with colorectal disease necessitating surgical treatment. The Intervention (I) investigated is robot-assisted surgery. This is contrasted with the Comparison (C) group, which underwent laparoscopic surgery. The outcomes (O) assessed encompass primary measures, such as operative time, duration of hospital stay, and overall complications. Secondary measures evaluated include the conversion rate, readmission rate, surgical site infection, lymph node yield, amount of blood loss, incidence of anastomotic leakage, and intestinal obstruction. The study type (S) criterion encompasses cohort studies, case–control studies, and randomized controlled trials (RCTs). Studies excluded from this research are those published in languages other than English or Chinese, non-comparative studies, conference abstracts, case reports, letters to the editor, and other unpublished manuscripts, ensuring a focused and relevant analysis of data.

Study screening and selection

Two independent authors (CZL and DQL) manually reviewed all records retrieved from the search process. In instances where consensus could not be reached between these authors, a third author (ZYB) was called upon to mediate and resolve any disputes. This collaborative approach ensured a thorough and unbiased selection process. Papers that aligned with the study's objectives were identified and selected for in-depth analysis through full-text review, facilitating a comprehensive and focused examination of the literature relevant to the research question.

Data items

Two evaluators conducted independent data extraction, meticulously gathering both general and specific details from each study. General information collected included the first author’s name, year of publication, and the country where the research was conducted. Demographic characteristics of the study populations, such as age, sex, and Body Mass Index (BMI), were also recorded. Furthermore, comprehensive outcome measures were extracted, encompassing operative time, the length of hospital stay, the incidence of overall complications, conversion rate to open surgery, readmission rate, instances of surgical site infection, lymph node yield, the volume of blood loss, rates of anastomotic leakage, and occurrences of intestinal obstruction. This thorough extraction process ensured a comprehensive dataset for subsequent analysis in the meta-analysis.

Statistical analysis

In this study, we used Review Manager V5.4.1 software provided by the Cochrane Collaboration, Oxford, UK, for statistical analysis. Results were expressed by 95% confidence intervals (CIs) and odds ratios (ORs) for dichotomous variables and weighted mean differences (WMDs) for continuous variables. For studies reporting data in medians, quartiles, or extreme values, we converted these data into means and standard deviations (SDs) using McGrath‘s [12] transformation method. In the analysis, the Cochran–Mantel–Haenszel method was used for dichotomous variables and the inverse variance method for continuous variables. We expected substantial heterogeneity across trials, prompting us to use a random-effects model for all analyses. To measure the heterogeneity of the studies, we used the I2 statistic, which defines 0–40% as low heterogeneity, 40–60% as moderate heterogeneity, 60–90% as significant heterogeneity, and 90–100% as high heterogeneity [13]. For this study, a p value less than 0.05 was considered statistically significant.

Bias risk assessment

Considering the inclusion of cohort studies in this paper, we utilized the Newcastle–Ottawa Scale (NOS) for evaluating bias risk in non-randomized controlled trials. This assessment involved a semi-quantitative star system with up to nine stars for literature quality. To test the stability of our findings, we adopted a 'leave-one-out' method, removing one study at a time to check the consistency of the results, acknowledging this could introduce variability. With ten or fewer studies included, the statistical power for detecting heterogeneity was limited, leading us to forgo additional publication bias analysis [14, 15].

Results

Baseline characteristics

Following our established search strategy and the defined criteria for literature inclusion and exclusion, eight studies were identified as meeting our requirements and thus were incorporated into our meta-analysis [6, 16,17,18,19,20,21,22]. Table 1 in our report meticulously details the characteristics and perioperative outcomes of these selected studies. Collectively, these studies encompassed a total of 5004 patients, with 1584 undergoing robotic-assisted surgery and 3420 receiving laparoscopic surgery. The selection process for these studies is visually depicted in Fig. 1 of our report, employing a PRISMA flowchart for clarity and transparency. In Table 2, we juxtapose key characteristics and variables extracted from these studies for comparative analysis. Our evaluation revealed no statistically significant differences in age (p = 0.48), body mass index (BMI) (p = 0.30), and the proportion of male participants (p = 0.29) among the groups, indicating comparable demographics across the study populations.

Table 1 Characteristics studied and perioperative outcomes
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Fig. 1
figure 1

PRISMA flowchart

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Table 2 Demographics of the studies
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Assessment of quality

In our analysis, studies were deemed high quality based on the Newcastle–Ottawa Scale (NOS) with a score of ≥ 7 stars. Consistently, all eight cohort studies included in our meta-analysis achieved a score of ≥ 7 stars, underscoring their high quality. Table 3 in our report provides a detailed breakdown of the quality assessment for these cohort studies, showcasing the rigorous standards employed in selecting literature for inclusion, thereby ensuring the reliability and validity of our findings.

Table 3 Study quality of case–control studies based on the Newcastle–Ottawa scale
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Primary outcome measures

A pool of 7 studies showed longer operative times in the robotic group compared to the laparoscopic group (WMD 37.53 mL, 95% CI 15.58–59.47; p = 0.0008) (Fig. 2A), a pool of 7 studies showed shorter hospital stays (WMD 0.68 mL, 95% CI −1.25 to −0.10; p = 0.02) (Fig. 2B), and a pool of 2 studies showed no significant difference in overall complications between the 2 surgical modalities (OR 0.72, 95% CI 0.36–1.46; p = 0.37) (Fig. 2C).

Fig. 2
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A Forest plots of operation time; B forest plots of hospital stay; C forest plots of overall complications

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Secondary outcome measures

After performing a meta-analysis after data collection of 8 included literatures, it was found that there was no significant difference in conversion rate (OR 0.45, 95% CI 0.19–1.06; p = 0.07) (Fig. 3A), surgical site infection (OR 1.11, 95% CI 0.88–1.41; p = 0.37) (Fig. 3B), readmission rate (OR 0.79, 95% CI 0.44–1.40; p = 0.42) (Fig. 3C), lymph node yield (OR 0.63, 95% CI −0.76 to 2.02; p = 0.37) (Fig. 3D), blood loss (WMD-31.32, 95% CI −70.53 to 7.88; p = 0.12) (Fig. 4A), anastomotic leakage (OR 1.32, 95% CI −0.86 to 2.02; p = 0.20) (Fig. 4B), intestinal obstruction (OR 0.93, 95% CI −0.43 to 2.03; p = 0.86) (Fig. 4C) between the two groups.

Fig. 3
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A Forest plots of conversion to laparotomy; B forest plots of surgical site infection; C forest plots of readmission; D forest plots of lymph node yield

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Fig. 4
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A Forest plots of estimated blood loss (EBL); B forest plots of anastomotic leakage; C forest plots of ileus; D forest plots of EBL after leave-one-out

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Sensibility analysis

In our meta-analysis, we observed considerable heterogeneity in certain outcomes, with I2 values indicating 90% for surgery duration, 70% for hospital stay length, and 91% for blood loss. To address these disparities and ensure the validity of our conclusions, we employed sensitivity analyses through the “leave-one-out” method, aimed at identifying sources of heterogeneity. A significant finding emerged during this process for blood loss: heterogeneity dramatically decreased from I2 = 91% to I2 = 0% after excluding studies by Panteleimonitis. This exclusion also highlighted a relative benefit for the robotic surgery group, which showed significantly less blood loss compared to the laparoscopic group (Weighted Mean Difference −49.23, 95% Confidence Interval −64.31 to −34.14, p < 0.00001) as depicted in Fig. 4C. Further analysis indicated a lower conversion rate to laparotomy in studies by Panteleimonitis [19], suggesting their influence on the overall heterogeneity observed study, relative to others, could primarily account for the reduced blood loss and, consequently, the initially high heterogeneity.

For operative time, length of hospital stay, and other outcomes with no significant heterogeneity, sensitivity analyses did not indicate any substantial changes in heterogeneity. This stability further affirms the reliability and robustness of our findings in these areas, suggesting that our meta-analytical results are both solid and trustworthy.

Discussion

Operation time

Our analysis, encompassing data from 7 studies, revealed that the operative time for the robotic surgery group was consistently longer than that for the laparoscopic group. Notably, Panteleimonitis et al [19]. reported a significant increase in operative time for obese patients undergoing robotic surgery—260 min compared to 215 min in the laparoscopic group (p < 0.001). On the other hand, Shiomi et al., who compared robotic and laparoscopic surgeries in 52 and 30 obese patients undergoing rectal surgery respectively, found the operative times to be 252 min for the robotic group and 238 min for the laparoscopic group, a difference that was not statistically significant (p = 0.390). Past studies have attributed the extended operative times in robotic surgery to the complexity and time demands of the robotic arm docking process [10], especially in rectal surgeries that require two docking stages. The first docking phase involves the removal of the inferior mesenteric vessels and the mobilization of the splenic flexure, followed by a second docking phase for detailed rectal work, which necessitates the redocking of the robotic system and the swapping of instruments. This twofold docking process not only prolongs the surgery duration but also increases the overall surgical workload [23]. However, there are discrepancies in these findings across studies. For instance, Ozben’s surgical team managed to control the docking time to within 10 min [24], and some studies have even reported shorter operative times for robotic surgeries [25]. Advances in robotic technology, including reductions in docking time and improvements in the manipulation system, are expected to mitigate the current limitations regarding operative time.

Moreover, it is important to consider that the differences in operative time, while statistically significant in some cases, may not be the decisive factor in choosing between robotic and laparoscopic surgical approaches. The choice of surgery method may hinge more on factors, such as the patient's condition, the surgeon’s expertise, and the specific advantages each technique offers in terms of patient recovery and surgical outcomes.

Length of stay

The analysis of seven studies revealed that robotic surgeries are associated with shorter hospital stays compared to laparoscopic surgeries. Ahmed et al [26] highlighted that robotic surgery, particularly in complex rectal cancer cases, resulted in lower conversion rates, less blood loss, and reduced hospital stay durations compared to laparoscopic surgery. Similarly, studies by Gorgun [18] and [19] found that obese patients undergoing robotic colorectal surgery had shorter hospital stays than those receiving laparoscopic surgery. It’s important to note that participants in both studies were part of enhanced recovery after surgery (ERAS) programs, which are known to expedite patient recovery and reduce hospital stays through a combination of strategies, including optimal pain management, stress reduction, early nutrition, and mobilization [27]. The observed reduction in hospital stay duration in the robotic surgery group could be attributed to fewer surgical complications, a hypothesis supported by recent studies from the Cleveland Clinic Group [28, 29]. These studies identified the length of hospital stay, readmission rates, and mortality as effective indicators of surgical complications. Therefore, the advantages of robotic surgery, including its potential to minimize surgical complications, could play a significant role in enhancing patient outcomes and recovery, further evidenced by the integration of ERAS protocols which amplify these benefits.

Overall complications

The combined analysis of two studies found no significant disparity in overall complications between robotic-assisted laparoscopic surgery (RALS) and conventional laparoscopic surgery (CLS). Specifically, one study demonstrated that the RALS group had fewer postoperative complications, as categorized by the Clavien–Dindo grades I–V, leading to a reduction in postoperative hospital stays when compared to the CLS group [20], a finding supported by both Panteleimonitis and Gorgun. Despite the increased operative times associated with robotic surgery, it was noted for consistently resulting in shorter hospital stays. However, there were no observable differences in the rates of conversion to open surgery, overall complication rates, or instances of anastomotic leakage between the two surgical approaches. Shiomi’s research also pointed out that among non-obese patients, a significantly lower proportion in the RALS group experienced Clavien–Dindo grade I or II urinary retention (0.8%) compared to the CLS group (8.3%). This indicates that robotic systems might offer superior surgical precision and more effective preservation of pelvic autonomic nerves, benefits that are particularly advantageous in challenging cases such as those involving obese patients.

Moreover, four retrospective studies [30,31,32,33] comparing robotic-assisted proctectomy to laparoscopic surgery, using ASC–NSQIP data, reported identical incidences of postoperative complications, including anastomotic leakage and surgical site infections, after both laparoscopic and robotic proctectomy. Voiding dysfunction, a crucial consideration in rectal surgery, was also examined. Kim et al [34]. reported that patients undergoing RALS experienced an earlier return to normal voiding function post-total mesorectal excision (TME), as evidenced by urodynamic analyses and IPSS scores, compared to those undergoing CLS. A recent meta-analysis comparing robotic-assisted laparoscopic surgery (RALS) and conventional laparoscopic surgery (CLS) for rectal cancer has underscored superior recovery of voiding and sexual function in the RALS group [35]. This improvement might be attributed to the reduced risk of nerve damage with robotic surgery, as the use of monopolar electric shears for pelvic autonomic nerve dissection allows for physical anatomical functions to be preserved, minimizing the risk of injury to pelvic visceral nerves [36].

Despite these findings, the limited data on complications within the included literature constrained further analysis of intraoperative and postoperative complications. Therefore, more high-quality clinical trials are needed to comprehensively assess the advantages and disadvantages of both surgical methods in obese patients, with a particular focus on utilizing the Clavien–Dindo classification to standardize complication reporting.

Conversion and rehospitalization rates

A meta-analysis involving five studies found no significant distinction in conversion rates to open surgery between robotic-assisted laparoscopic surgery (RALS) and conventional laparoscopic surgery (CLS) in obese patients. This result is consistent with the findings of Panteleimonitis S and Gorgun, where Gorgun et al. retrospectively analyzed 29 patients undergoing robotic rectal surgery compared to 27 patients undergoing laparoscopic surgery. Although a lower percentage of patients required conversion to open surgery in the robotic group, the difference did not reach statistical significance (3.4% vs. 18.5%, p = 0.09). Conversion to open surgery serves as a pivotal indicator of the technical challenges associated with minimally invasive procedures. In the context of colon cancer treated with laparoscopic surgery, conversion to open surgery has been associated with heightened mortality, morbidity, and diminished survival rates, underscoring its significance as a gauge of the efficacy and oncological suitability of minimally invasive approaches. The ROLARR study [37], the largest randomized controlled trial (RCT) to date comparing robotic and laparoscopic rectal resections, found no significant difference in conversion rates between the two techniques (8% vs 12%, p = 0.16). However, more recent studies [25, 38] and meta-analyses [39, 40] have indicated significantly lower conversion rates with RALS, suggesting that the advanced capabilities of robotic technology, such as three-dimensional visualization and 360-degree articulation, may address the limitations faced by laparoscopy in obese patients. Factors such as male gender, preoperative weight loss, advanced neoplasia, and hypertension have been identified as additional risk factors for unplanned conversion to open surgery in both laparoscopic and robotic colorectal surgeries [41]. Despite these insights, the limited data available in the current literature precludes a detailed analysis of these factors impact on conversion rates, underscoring the need for high-quality clinical studies with larger sample sizes to further explore these differences.

In terms of rehospitalization rates, the meta-analysis of four articles found no significant differences between the two surgical approaches. However, recent studies offer contrasting evidence. For instance, Shiomi et al. reported lower blood loss and complication rates in the robotic group compared to the laparoscopic group, with associated studies from the Cleveland Clinic suggesting that the length of hospital stay, readmission rates, and mortality can serve as effective predictors of complications [28]. In addition, Panteleimonitis et al. found that the 30-day readmission rates were significantly lower in the robotic group compared to the laparoscopic group (6.3% vs 19.7%, p = 0.033), further indicating the potential advantages of robotic surgery in certain outcomes.

Blood loss

A meta-analysis incorporating data from four studies initially found no significant difference in blood loss between robotic-assisted laparoscopic surgery (RALS) and conventional laparoscopic surgery (CLS) in obese patients. However, the subsequent exclusion of the study by Panteleimonitis from the analysis revealed a notable difference favoring the robotic group, with significantly less blood loss compared to the laparoscopic group (Weighted Mean Difference (WMD −49.23, 95%CI −64.31 to −34.14; p < 0.00001). This finding is supported by Shiomi et al., who also reported reduced blood loss in the robotic group (10.5 vs 34 ml, p = 0.002). The observed reduction in blood loss during RALS could be attributed to the advanced features of robotic platforms, which offer stability, flexibility, tremor filtration, motion scaling, and intuitive controls for precise and sharp cuts. These technological advantages are particularly beneficial in managing the challenges posed by visceral adiposity in obese patients, allowing for more accurate dissection and reduced risk of bleeding.

However, larger multicenter prospective observational studies are still needed to validate these results.

Follow-up outcome

The limited scope and quantity of literature data incorporated into this article restrict the feasibility of conducting further meta-analyses on long-term outcome measures, representing a significant limitation of this study. Presently, available evidence indicates that robotic surgery (RS) is on par with laparoscopic surgery (LS) regarding long-term oncologic outcomes [42]. Recent research has also reported satisfactory results for both robotic and laparoscopic techniques concerning short-term oncologic outcomes, including the integrity of the mesorectal fascia, the status of circumferential resection margins, and the number of lymph nodes harvested [43]. Nonetheless, the specific evidence about outcomes in obese patient populations remains scarce. Given this gap, there is a clear need for more extensive long-term follow-up studies focused on colorectal cancer surgery outcomes in obese patients to better understand and optimize treatment efficacy and safety in this demographic.

Cost

The relatively high cost associated with robotic surgery is acknowledged as one of its main disadvantages [37]. According to Matei et al [44], the expense for each robotic procedure is approximately 3840 euros. In addition, Salonia et al [45]. highlighted in their human research that acquiring a da Vinci surgical system incurs a cost of about 1.5 million dollars, with an annual maintenance fee amounting to 10% of the purchase price. However, the introduction of new systems, improvements in device longevity, and the increasing coverage of such procedures by health insurance are contributing to a gradual reduction in the costs associated with robotic surgery.

Limitations

This article primarily exhibits the following limitations. First, the meta-analysis was restricted by the limited quantity of included literature and data, thereby preventing further subgroup analysis and examination of follow-up outcomes. Second, out of the eight included studies, all were cohort studies, implying the necessity for larger randomized trials to furnish more dependable evidence for the findings derived from the pooled analysis. Finally, discrepancies exist concerning the definition of obesity and the criteria used to define conversion to open surgery, which may introduce variability into the interpretation of results.

Conclusions

In summary, robotic-assisted colorectal surgery for obese patients is effective and safe, offering benefits like reduced hospital stay and less blood loss compared to laparoscopic surgery, but it requires longer operation times without significant differences in complications or rehospitalization rates. Further research through larger, multicenter randomized controlled trials is essential to validate these findings comprehensively.