Is There a Difference in Laterality During Robot-Assisted Radical Prostatectomy? Assessment of Lymph Node Yield and Neurovascular Bundle Dissection

Introduction

S ince its introduction in the United States in 2000, the da Vinci Surgical System (dVSS) (Intuitive Surgical, Sunnyvale, CA) has become increasingly used in oncologic surgical procedures in urology. In fact, about 98,000 robot-assisted radical prostatectomies (RARP) were performed worldwide in 2010, accounting for 60% to 70% of all radical prostatectomies. ^1,2 Advantages of the minimally invasive approach include decreased intraoperative blood loss and complication rates, shorter in-hospital recovery, less postoperative pain, fewer postoperative complications and, in some series, a faster return-to-function. ^{2 –4}

A review of outcome-based studies has shown that RARP has improved perioperative outcomes, such as operative blood loss, transfusion rates, and length of hospital stay when compared with open prostatectomy. In addition, many studies suggest that RARP has lower rates of positive surgical margins (PSMs), although others found differing results. ⁵ RARP has been equivalent to open prostatectomy with respect to short-term functional and oncologic outcomes. ^{4 –8} Furthermore, robot-assisted procedures have the added benefits of increased visualization, magnification, and maneuverability without the steep learning curve of conventional laparoscopic surgery. ^3,9

Because of its wristed instrumentation, tremor corrective technology, magnification, as well as the advanced three-dimensional visualization, the robot has been shown to increase surgeon dexterity when compared with laparoscopic surgery. ⁹ The dVSS has also been shown to overcome innate hand dominance, especially in novice surgeons. ¹⁰ A number of limitations of RARP have been identified, however, which include a high cost, lack of tactile feedback to the surgeon, and limited long-term oncologic and functional data. ¹¹

To our knowledge, no previous studies have been performed to investigate the presence of inherent “handedness” of the dVSS with respect to actual operative outcomes. In this study, we identified the pelvic lymph node (LN) as well as the neurovascular bundle (NVB) dissections as procedure points during RARP that could be influenced by laterality and sought to illustrate left-right consistency.

Patients and Methods

The Institutional Review Board-approved Columbia University Oncology database was queried for patients who had undergone RARP by a single right-handed surgeon (KKB) over a 2-year period (2008–2010). A total of 367 patients with complete medical records were identified.

Operative reports were reviewed to establish intended LN dissection (limited vs extended) as well as the intended degree of nerve preservation (wide, standard, or lateral prostatic fascia sparing). The total as well as positive LN yields were recorded for each patient and stratified by side. Limited LN dissection was defined by Studer zone 1 (external iliac and obturator). A dissection was deemed extended if it included Studer zones 1 and 2 (external iliac, obturator, and internal iliac). ¹² The LN dissection template used was at the discretion of the surgeon on a case-by-case basis dependent on patient and tumor characteristics. In 16 patients, unilateral extended LN dissection was performed because of contralateral scarring secondary to previous abdominal surgeries or, on rare occasion, for unilateral low-volume intermediate- or high-risk disease. All cases were performed using a four-arm dVSS as previously described, ¹³ with six port sites, and a single bedside assistant on the right side of the patient as described by Menon. ¹⁴

A subset of 93 consecutive men underwent RARP between March 2008 and May 2009 with prospective assessment of fascial widths (FW) after NVB dissection. Extent of NVB dissection was based on prostate cancer characteristics and clinical stage at diagnosis and was determined preoperatively. All analyses were performed in an intention to treat fashion. Patients were stratified by intended NVB dissection: Wide=wide resection to maximize surgical margin; standard=nerve-sparing technique as described by Walsh and Donker ¹⁵ to preserve the posterolateral bundle; and lateral prostatic fascia sparing=incision of the levator and anterior prostatic fascia high over the prostate, developing the plane between the prostatic capsule and the NVB. ¹⁶ Criteria for lateral prostatic fascia sparing technique were primary Gleason score of 3, prostate-specific antigen (PSA) level <10, clinical stage T_1c, and <50% of any core positive. An independent investigator who was blinded to the intended dissection measured the FW under the direction of an experienced uropathologist. FW was determined by measuring the distance between the outermost prostate gland and surgical margin using an ocular micrometer. The right FW was measured between the 7 and 8 o'clock positions and the left between the 4 and 5 o'clock positions.

The Wilcoxon rank sum test was used to compare the median LN yield between the limited and extended LN dissections. A two-tailed Student t test was used to compare the mean FWs at corresponding points on both sides of prostatectomy specimens in the nerve-sparing techniques as well as the left-right consistency of the LN dissection. The statistical significance in this study was considered at P≤0.05. All analyses were performed with Stata^® 11.0 SE (StataCorp LP, College Station, TX).

Results

A total of 340 limited, 11 bilateral extended, 11 right extended, and 5 left extended LN dissections were performed. Patient characteristics are shown in Table 1. Median preoperative PSA was higher in the patients who underwent an extended LN dissection. In addition, clinical T stages and Gleason scores were higher in the extended LN dissection group. Overall mean age at RARP was 60 years with a mean preoperative PSA of 6.9 ng/mL. There was a higher yield in number of LN on the right compared with left for patients undergoing a limited LN dissection (3.26 vs 2.76, P=0.010; range 0–20 on right and 0–13 on left); however, there was no difference in the number of positive LNs (P=0.77). There was no difference in LN yield between sides (4.41 vs 4.37, P=0.96; range 1–12 on right and 1–11 on left) or the number of positive LN per side (P=0.63) for patients who underwent an extended LN dissection. When comparing the total LN yield by dissection extent, there were more LNs removed during an extended LN dissection both on the right (3 vs 4, P=0.01) and on the left (2 vs 4, P<0.01).

Comparing the surgical result of right and left sides according to nerve-sparing techniques, there was no statistically significant difference in FW between right and left for the wide or lateral prostatic fascia sparing techniques (Table 2). For patients who had undergone standard NVB preservation, the FW on the left lateral positions were wider than the corresponding positions on the right (P<0.001), indicating a less precise dissection (Table 2).

A PSM was identified in 15.5% of patients (57/367). Of patients with a PSM, 16 (28%) had their PSM on the right side only, 24 (42%) had their PSM on the left side only, 14 (25%) had bilateral PSMs, and 3 (5%) could not be lateralized.

Discussion

In this study, we report an observed difference in right and left LN yields in patients undergoing a limited LN dissection during RARP. In addition, the periprostatic fascia was more narrow (precise) on the right compared with the left when performing the standard nerve-sparing technique. Finally, there was a higher rate of PSMs on the left than on the right. These discrepancies can be because of a number of etiologies, including the dexterity of the surgeon, fixed instrument laterality, port placement configuration, patient positioning, or assistant positioning. To our knowledge, there have been no previous reports describing an intraoperative discrepancy in robot laterality.

In our report, there was a discrepancy in LN yield by side when performing the limited LN dissection. This difference was not observed when the extended LN dissection was performed. There are a number of possible explanations for this finding. First, the sample size for the extended LN dissection is fairly small with only 27 patients compared with the 340 patients who underwent a limited LN dissection. Perhaps with the inclusion of additional patients, a preferred laterality will be evident. Alternatively, when the surgeon is forced to concentrate on LN yield, as with the extended LN dissection, the surgeon may be able to overcome inherent difficulties caused by instrumentation that are apparent in the limited left-sided LN dissection. This is further seen when comparing the results of the standard NVB dissection with the results of the lateral prostatic fascia sparing dissection. With increased attention to achieve a closer dissection bilaterally, this observed laterality preference is negated.

A number of reports demonstrate the effect of the da Vinci on surgeon handedness and dexterity. Moorthy and associates ⁹ conducted a study to quantify the enhancement of surgeon dexterity with the use of the da Vinci robot vs the laparoscopic approach. Ten surgeons with varying endoscopic suturing experience were asked to place three sutures on a pad laparoscopically, robotically with two-dimensional vision, and robotically withthree-dimensional vision. Their results indicate that surgeons using robotic instruments had an improvement in economy of motion and overall time needed to complete the tasks. These improvements were further augmented with the addition of three-dimensional visualization. The authors conclude that the “wristed instrumentation,” tremor-correction technology, and motion scaling enhance surgeon dexterity by nearly 50% when compared with the laparoscopic approach. This report, however, only compares the different approaches and did not specifically address differences in tasks by hand.

To determine whether the da Vinci system overcomes innate surgeon hand-dominance, Mucksavage and colleagues ¹⁰ enrolled 19 robotic novices to perform the Purdue Pegboard test ¹⁷ as well as a needle targeting test both using their dominant and nondominant hands and following introductory training. These tasks were performed twice for each hand, both open and with the use of the dVSS. With the open approach, there was a statistically significant difference in the performance of both tasks by hand reflective of the surgeons' handedness. This difference was not observed when performing the tasks with the dVSS. The authors conclude that the da Vinci is capable of eliminating innate dexterity or handedness among novice surgeons. While the difference between hands seems to have improved in this study, performance of both tasks was worse using the dVSS than open. The observed findings are likely the result of novice surgeons performing simple tasks on a novel platform. Experience with the dVSS over time would likely allow for the expert's handedness to manifest itself given the dVSS’ fidelity between the surgeon's actions and the robot's movements.

While surgeon handedness is a potential cause of a laterality difference, port placement and assistant positioning may play a role in the difference in outcomes by laterality. A number of techniques have described port placement for the robotic arms and for the assistant access. The technique described by Tewari and coworkers ¹⁸ advocates for the placement of a total of six ports with two bedside assistants. The camera is introduced through a 12-mm port placed at the umbilicus, while the two instrument arm ports are placed 10 cm from the midline at the level of the anterior superior iliac spine. In addition, two assistant ports are place on the right side for retraction and suction, and the sixth port is located in the left lateral flank inferior to the robotic arm port. Alternatively, however, methods have been described using a single assistant and five port sites. ¹⁹

Hemal and colleagues ²⁰ have reviewed optimal port placement as well as optimal number of patient-side assistants. These data, however, describe use of the three-armed da Vinci robot. In our study, the four-armed da Vinci was used as previously mentioned. In this study, ports were placed using the method described by Menon and associates, ¹⁴ which has been shown to have satisfactory postsurgical oncologic and functional outcomes. ^21,22 In the aforementioned reports, no authors have analyzed differences in laterality outcomes based on port placement or assistant positioning.

The results of this study remain to be validated. If corroborated, however, there are a number of potential implications of an inherent robotic handedness. Perhaps some aspects of the procedure that contribute to functional and oncologic outcomes can be further improved on by correcting for this laterality. In our study, we found a wider mean width of the periprostatic fascia on the left compared with the right. In addition, we had a higher PSM rate on the left than on the right. Therefore, while the width was thicker, there may have been more variability in the dissection itself, leading to the higher PSM rate. By making the surgeon aware of this laterality, outcomes can potentially be improved. This can be achieved by maintaining a high focus level while performing procedures bilaterally with the goal of minimizing laterality-borne discrepancies.

Our study has limitations that warrant mentioning. Because it is retrospective and observational, factors determining the extent of LN dissection and nerve-sparing technique, such as patient and tumor characteristics, can also be contributing to the differences in outcomes by laterality. In addition, LN yield could be affected by the perseverance of the uropathologist and the method of LN packet preparation for assessment (eg, palpating the packet for nodes vs sectioning the entire packet). While these methods used by the pathologist will affect the ultimate node yield, the method is applied bilaterally and should not affect differences by side. Furthermore, only one right-handed robotic surgeon was included in this study for the purposes of consistency of technique. It would be ideal to analyze several right-handed, left-handed, and ambidextrous surgeons, and varying instrument configurations to identify the exact contributors to the differences in outcomes by side. A follow-up study that prospectively changes robot arm configurations and bedside assistant positioning tailored to the individual patient's anatomy and pathology would be of interest.

Conclusions

Our findings illustrate that using the dVSS for RARP yielded a greater number of LNs and a closer intended NVB dissection on the right compared with the left. This difference can be attributed to surgeon handedness, specific robotic instrument laterality, or possibly assistant instrument laterality. The implications of a robotic side-preference are of importance, because many procedures rely on the precise movements of the dVSS. The knowledge of an inherent preferred laterality would allow surgeons to adapt their technique and potentially improve both short- and long-term postoperative oncologic and functional outcomes. Further studies are needed to identify the cause of this difference and investigate whether awareness of this difference or changes in practice would result in improvements in outcomes.