Introduction

The benefits of endoscopic procedures have been well demonstrated in the literature. The advantages are mainly related to reduced hospitalization, postoperative pain, complications rate, and consequently a consistent improvement in patients’ quality of life [1]. In the last years, the concept of ultra-minimally invasive surgery (U-MIS) took place with the effort to minimize the number of trocars used and the size of instruments. The decrease in the size of the ports was obtained with the innovation of 3 mm and percutaneous instruments, while the reduction in the number of trocars was achieved with the use of single-port devices [2,3,4,5,6,7,8,9,10,11].

Since their approval and marketing in 2005, robotic platforms acquired progressive importance in different surgical fields, such as urology, gynecology, and general surgery. Through the years, new surgical robots [12,13,14] have become available and others are in an experimental phase. Of note, also in the field of robotic surgery, one of the directions for innovation and technology improvement has been the reduction in the instrument size [15] and the use of single port. Regarding this latter aspect, robotic single-site surgery has been extremely useful to overcome the ergonomic limitations and the long learning curve of standard single-port laparoscopic surgery.

The objective of this article is to present the existing clinical evidence on the use of single-port robotic-assisted platforms in different surgical fields such as general surgery, gynecology and urology. When data were available, we also reported the cost analysis of these procedures.

Materials and methods

The present review was designed to incorporate population criteria, surgical interventions, and outcomes. The systematic search was modeled in agreement with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement (PRISMA) [16, 17], and it was registered in the International Prospective Register of Systematic Reviews (available at http://www.crd.york.ac.uk/PROSPERO; CRD 42018108068). The terms “LESS” OR “single port” OR “single site” AND “robot” OR “robotic” were systematically used to search the PubMed and Scopus databases. A hand search of the references of both potentially relevant articles and articles qualifying for inclusion was also performed. Original reports in English language were identified, with the purpose of including all relevant papers regarding robotic single-site surgery in three of the main possible applications of this technique (i.e., general surgery, urology and gynecology). Exclusion criteria included duplicate publications, non-English language literature, case series including less than 10 single-site robotic procedures, letters, editorials, different fields of application and then general surgery, urology and gynecology and reviews to avoid repetition of studies results. The flow diagram of the detailed process of selection of articles for inclusion in the review is reported in Fig. 1.

Fig. 1
figure 1

Flow diagram of the detailed process of selection of articles for inclusion in the review

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The principal findings considered in the present review were: the study design, the number of patients included in each study, operative time, estimated blood loss (EBL), conversion rate to multiport robotic or standard laparoscopy or laparotomy, postoperative complications, postoperative hospital stay, costs analysis (when provided by the studies), and the possible advantages and disadvantages reported by the authors of the studies.

Statistic analysis

A meta-analysis of the comparative studies was performed using the Cochrane Review software (Review Manager version 5.3 for Windows; Cochrane Community, London, UK), in order to assess the rate of complications and conversions to laparotomy of single-site robotic surgery, compared to conventional standard techniques (standard robotics, LESS and standard laparoscopy). No meta-analysis was conducted regarding operative time, estimated blood loss and hospital stay, due to the large heterogeneity of the studies included. A Chi-square test for heterogeneity among proportions was used to determine the presence of statistical heterogeneity between studies in terms of surgical-related complications and success rate.

Random effect model was used. Forest and funnel plots were created for each comparison; P values < 0.05 were considered statistically significant.

Results

A total of 57 studies were considered eligible for the present review (flow diagram Fig. 1). The articles included were divided according to the surgical field in which the study was conducted: General surgery (29 articles), Gynecology (18 articles), Urology (10 articles).

General surgery

We selected 29 studies published between 2011 and 2018, consisting of 14 case–control and 15 case series.

Perioperative data, rate of conversion, complications, and authors comment are reported in Table 1.

Table 1 Studies referring to robotic single port in general surgery
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General surgery procedures represent the largest application of robotic single port (RSP) described in the literature. Five studies with more then 200 patients have been reported [18, 40, 41, 43, 46]. The most frequent procedure performed with RSP is cholecystectomy, but also bowel resections and adrenalectomies have been reported. Most of the studies describe that the operative time for RSP cholecystectomy ranges approximately between 60 and 120 min. Instead for adrenalectomy and colectomy, the time required is mainly between 100 and 230 min.

In some studies, the operative time was significantly increased for RSP if compared with standard laparoscopy (SLPS) or laparo-endoscopic single site (LESS) [20, 36, 44, 45]. A shorter operative time is reported in case of RSP-reverse [23]. Other studies do not confirm the disadvantages in terms of operative time using RSP [18, 22, 26, 34, 44, 46]. The authors attribute the different results obtained to the variable experience of the surgeons involved. In a study by Svoboda et al. [41], the population was stratified on patients’ BMI. The results of this report showed that patients with BMI ≥ 30 have a significantly prolonged operative time.

All studies report minimal EBL for RSP cholecystectomy, while adrenalectomies were more frequently related with major EBL, although no studies reported statistically significant differences with other techniques. The conversion rate, especially for cholecystectomies, is acceptable. Balachandra et al. [18] reported a large series of 678 cases (415 RSP, 263 SLPS) in which the rate of conversions from RSP to SLPS and from RSP to laparotomy (LPT) was 2.9% and 3.2%, respectively. No significant differences in terms of conversions were detected when comparing different surgical approaches. Hospital stay ranges between 1 and 4 days in the majority of the studies selected, although series including complex procedures such as colectomy and adrenalectomy describe a tendentially longer average hospital stay. Some comparative studies [18, 23, 36, 40] report that RSP is associated with a shorter hospitalization, compared to SLPS and LESS. However, other studies such as Kudsi et al. [20] and Arghami et al. [26] did not report significant differences between RSP and other techniques.

The majority of the complications reported in the studies included were minor (grade 1–2). Umbilical wound infections and umbilical incisional hernias represent the most frequently reported adverse events.

In the study by Juo et al. [28] is reported a G5 complication consisting of a stroke in a patient died during post-operatory.

Urology

We selected ten studies published between 2010 and 2016, consisting of four case–control studies and six case series.

Only in three studies, there were more than 50 patients enrolled. The procedures performed consisted of pyeloplasty, prostatectomy, partial/radical nephrectomy, and cystectomy.

Perioperative data, rate of conversion, complications and authors’ comments are reported in Table 2.

Table 2 Studies referring to robotic single port in urology
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Regarding operative time, Law et al. and White et al. [47, 50] reported no significant differences between RSP and RMP and SLPS, respectively. Instead, Shin et al. [52] reported a prolonged operative time for (RSP) (P = 0.03) compared with robotic multiport (RMP); these data were confirmed by Olweny et al. [54] that compared RSP with LESS (P = 0.007). The estimated blood loss reported in the different studies is very variable, between 50 and 550 ml. These data are probably due to the different procedures performed and the different surgeons’ experiences. However, it is noteworthy that in the case–control studies no significant differences were reported.

We distinguished conversions to multiport technique robotic or standard laparoscopy (SLPS) (approximately between 5 and 30% in the different studies included) and laparotomy (LPT) (reported in four studies [51, 53, 55, 56] between 1 and 6%). The hospital stay was similar across the different studies (between 2 and 6 days), depending on the surgical procedure performed. Of note, in case–control studies, no significant difference was recorded excluding the study by White et al. [51] in favor of RSP (although in that study the sample was 10 patients per arm).

Postoperative minor complications grade 1–2 were rare, and in case–control studies no significant differences were registered when comparing RSP to other techniques. Four studies [60, 62, 64, 66] report grade 3–4, ranging between 3 and 20%. The most frequent major complications (grade 3) were related to the umbilical incisional site (i.e., dehiscence, hernia, or infection).

Gynecology

We selected 18 studies published between 2013 and 2018 consisting of 11 case series and 7 case–control studies.

Perioperative data, rate of conversion, complications, and authors’ comments are reported in Table 3.

Table 3 Studies referring to robotic single port in gynecology
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The majority of the studies on gynecologic procedures included less than 100 patients, and most of them have no control group.

The most frequently reported procedure was hysterectomy, but also adnexal surgery, myomectomy, and sacrocolpopexy have been described. The operative time is extremely variable due to the inclusion of different procedures; the mean average operative time for hysterectomy was between 100 and 150 min. Most of the case–control studies [62,63,64, 67, 70] compared RSP with RMP and LESS. While some studies reported a similar operative time when comparing RSP and LESS [59, 62, 67, 73], others [64, 65, 70] described an advantage of standard single-site laparoscopy over RSP.

In the majority of the studies, the mean EBL reported is minimal (< 100 mL). One series of myomectomies [68] reports a mean EBL of 135 mL. In the studies by Bogliolo et al. and Paek et al. [64, 65], a significant difference in terms of EBL was reported in favor of RSP, respectively, compared with RMP and LESS. Only in one study by Fagotti et al. [67], the difference in terms of EBL between RSP and LESS was significant in favor of LESS, while in the rest of the case–control studies no significant differences were recorded [59, 63, 70, 73].

The rate of conversion ranged between 0 and 5% and case–control studies did not identify any significant difference between RSP and other minimally invasive techniques. Several studies have reported the use of a supplementary ancillary port, in addition to the single-port trocar or conversion to SLPS or RMP. In one study by Vizza et al. [74], a conversion to vaginal surgery was reported.

The hospital stay varied between 1 and 6 days, depending on the type of procedure performed. Both Bogliolo et al. and Fagotti et al. [65, 67] reported a significant reduction in hospital stay in favor of RSP. The other case–control studies did not confirm these results.

The complication rate reported in the studies is very low, being < 10%, except for one prospective study by Vizza et al. [74] where, in a series of 20 patients, a 20% rate of major complications is described (pelvic abscess, bowel perforation, and vaginal dehiscence).

Among the major complications reported in the gynecologic literature, hemoperitoneum, ureteral injury, and vaginal vault dehiscence have been described.

Meta-analysis

Considering all the data available (irrespective of the surgical branch of application), we performed a meta-analysis to compare the RSP with the principal three reference procedures: SLPS, RMP, and LESS. We focused our analysis on two principal factors: conversion rate and complications.

Regarding conversion rate, Fig. 2 shows that there is no significant difference in terms of conversion to laparotomy when RSP is compared to SLPS (P = 0.87), LESS (P = 0.67) RMP (0.97).

Fig. 2
figure 2

Comparison of different techniques (RSP, RMP, LESS, SLPS) in conversion rate

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When considering complications (Fig. 3), we found that RSP is associated with a significantly higher risk of any adverse event, compared to SLPS (P = 0.002). Also the comparison between RSP and LESS showed a tendency toward a higher risk of complications in the patients approached by RSP, although this did not reach statistical significance (P = 0.08). Conversely, when RSP is compared with RMP no difference in terms of complications has been recorded (P = 0.60).

Fig. 3
figure 3

Comparison of different techniques (RSP, RMP, LESS, SLPS) in complication rate

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Discussion

The present review provides a summary of the available studies on single-port robotic surgery. Of note, no randomized trial has been published on this issue and no good-quality evidence is available; as a consequence, we have to rely only on case series and few case–control studies.

LESS is a well-known procedure that was deeply investigated in the past [9, 10]. After an initial enthusiasm, especially related to a possible improvement in cosmetic outcomes, the procedures performed using this technique resulted to be more difficult and the learning curve was prolonged. In the literature, the principal criticism was the absence of triangulation (which represents a crucial point for every surgical procedure) and the instrument clashing. The results of these limits were a long operative time and a high difficulty in performing major procedures.

In this context, the implementation of robotic technology in single-site surgery represents a fundamental improvement in this field because it theoretically overcomes the ergonomic limits and the absence of triangulation, thanks to the robotic arms. Moreover, other advantages over conventional laparoscopy are greater dexterity, tremor filtration, and tridimensional vision [75].

More specifically, during LESS, as laparoscopic instruments are inserted into the abdominal cavity through a single incision, there can be a tendency to cross them just below the abdominal wall to obtain a separation between instrument tips without external collision of the hand-pieces. This crossing of the instruments allows a better range of motion, but the resultant reversal of handedness introduces a major mental challenge for the surgeon. Moreover, as reported in literature [47, 54, 55], in older RSP versions the absence of EndoWrist instruments reduce the possibility to obtain a correct traction on tissues and lifting up of organs, especially if the traction direction is parallel to the instruments. This aspect could influence the surgical outcome. Nevertheless, with the development of bent instruments and new port devices, triangulation can be restored in proximity of the target [75].

The robotic instruments cross at the abdominal wall to have the right instrument on the left side of the target and the left instrument on the right. To correct for the change in handedness, the robotic console was instructed to drive the left instrument with the right-hand effector and the right instrument with the left-hand effector. In this way, collision of the external robotic arms was prevented [75].

The next innovation step was made by Intuitive Surgical that furnished new dedicated software to RSP instruments described by Autorino et al. [75] and consists of a multichannel access port with two curved cannulas for robotic instruments and other two straight cannulas. The curved cannulas are integrated with the system and allow the instruments to obtain triangulation.

Same-sided hand-eye control of the instruments is maintained through assignment of software of the Si system that enables the surgeon’s right hand to control the screen right instrument even though the instrument is in the left robotic arm and, reciprocally, the left hand to control the screen left instrument even though the instrument is in the right robotic arm. The second part of the platform is composed by semirigid, non-wristed instruments. Using this setting, the instruments fighting is reduced because the curved cannulas angle the robotic arms away from each other. Internal collisions with the camera are avoided because the camera is designed to be placed in the middle of the curved cannula zone.

Specific comments by field of application

General surgery

In our analysis, we reported also the comments of the authors on the possible advantages and/or disadvantages of RSP. Some studies [20, 22, 36] evaluated patients’ self-reported cosmesis following surgery: A better outcome was described following RSP, compared to SLPS.

Other authors [18, 26, 39] reported a statistically significant decrease in analgesic drugs use with RSP and reduction in painkillers. One study [39] performed a cost analysis of the different procedures, reporting a significant increased cost of RSP compared with SLPS, while Balachandra et al. [18] reported a higher incidence of umbilical incisional hernias and wound infections.

Urology

The more frequent advantages identified by the authors are represented by the reduction in instrument clashing and surgical advantages thanks to the 3D vision and the intuitive system of maneuver. Two studies [52, 53] are in accordance regarding the ergonomic advantages of RSP and the better cosmetic outcomes, compared with RMP. Some studies [50,51,52] reported a significant reduction in postoperative pain in favor of RSP, compared to standard technique (P < 0.04). Some authors [47, 54, 55] reported disadvantages related to the difficulty in tissue traction and instruments fighting, for procedures performed without EndoWrists.

Gynecology

A better cosmetic outcome and an enhanced learning curve were reported by several studies in favor of RSP, compared to RMP and LESS, respectively [62, 72, 74]. On the other hand, increased costs and longer operative time have been described using different techniques. When comparing RSP and RMP techniques, two authors [65, 73] described a cost reduction for procedures performed with RSP.

In accordance with other studies from other specialties, the most frequent disadvantages reported using RSP are prolonged operative time and a longer learning curve.

In an interesting study by Choy et al. [68], a better dexterity to gain stronger suture is reported using RSP. Considering that in procedures such as myomectomy this aspect is fundamental, it could be an important advantage in all surgeries requiring large number of sutures.

Vizza et al. [74] provided an insightful comment regarding the fact that there are still few electrosurgical options in RSP technology.

General considerations

At the end, considering the results of our meta-analysis, an interesting finding is the fact that we recorded a statistically significance increment of complications using RSP if compared with SLPS and a trend (P = 0.008) when RSP is compared with LESS. These data are probably related with the fact that RSP platforms represent a relatively new development and the surgeons have a higher experience with standard techniques instead of robotics. However, in our opinion the possibility to reduce the surgical invasiveness maintaining the same level of performance is crucial. The actual limits of RSP should not discourage surgeons but should represent a base in which further efforts will allow better operative outcomes.

In this context, apart from the technological innovations, the learning curve represents a fundamental step to overcome the RSP limits, including the increased complication rate. In a study by Spinoglio et al. [45] a comparative learning curve study was conducted, demonstrating the superiority of RSP over LESS. Considering the available literature, often reporting small series, it is clear that the RSP is in an initial phase, needing systematic practice to standardize the surgical procedures with the aim to obtain comparable outcomes with respect to RMP in terms of operative time and complication rate.

A possible effective way to reduce complications may be the addition of a supplementary port, in order to overcome possible issues related with triangulation and traction. Of course this suggestion deserves adequate investigation in the next future.

This opinion is supported by the fact that the comparison of two robotic platforms (RSP vs RMP) did not show any statistical differences in terms of complications (P = 0.60).

Instead, the comparison of different techniques in terms of conversion to laparotomy did not show any significant difference. In our opinion, this is probably related to the attention dedicated during robotic procedures and the consequent prolonged operative time.

Another important aspect is the costs analysis of RSP. In our study, we found two general surgery studies by Su et al. and [39] Konstantinidis et al. [32], reporting an increase in costs when using RSP. On the other hand, two gynecologic studies by Corrado et al. [57] and Bogliolo et al. [62] did not confirm this difference. The discordance is probably related to the balance of operative time and hospital stay. Of course, increased operative time causes are associated with higher costs; however, a reduction in hospital stay may allow a profitable balance in favor of RSP. However, we have to acknowledge that costs are dependent on a large number of possible variables and further investigations about this aspect is needed to allow an exact estimate on this issue.

Future perspectives

In the next few months, new robots will be launched on the market, including single-port platforms. One of the most intriguing aspects of this new generation of robots is the fact that new fully articulated instruments and optical cameras with snake-like movements will become available. The obvious consequences will be the possibility to perform a more comfortable surgery, with potentially all the advantages of multiport approach, but requiring only a small incision in the umbilicus. This type of approach may allow the robotic system to enter in a new era with real and consistent advantages over traditional laparoscopic surgery.

Future platforms should incorporate a higher range of movements to improve dexterity, more effective electrosurgical (possibly multifunction) options, smaller caliber instruments to decrease the size of the umbilical incision, and possible complex articulating devices, allowing the maintenance of triangulation and an adequate traction and exposure of tissues.

In parallel to single-port robotic surgery, other forms of robotic platforms will be available, such as machines allowing hybrid procedures in which laparoscopy or open surgery will take an advantage from the use of dedicated robotic arms.

The strength of our study is the fact that it is a comprehensive picture of the present status of single-port robotic surgery, reporting its major applications.

At this moment, evidence does not support the use of single-port robotic surgery in clinical practice.

However, it is logical to hypothesize that new technological improvements will strongly enhance the utility of RSP in all the abdominal surgical fields.