Wolf Piranha vs Storz Prostate Morcellation Devices: A Retrospective Multi-Institutional Study

Introduction

Holmium laser enucleation of the prostate (HoLEP) is an increasingly popular technique for surgical management of benign prostatic hypertrophy with lower urinary tract symptoms refractory to medical management in both the United States and abroad. ¹ While it is known to have a relatively steep learning curve, ² it has been shown to have improved perioperative and long-term outcomes compared with more traditional treatment options and low overall complication rates compared with more traditional methods of prostate resection. ^3,4 It has been particularly efficacious while maintaining low morbidity and complications in patients with very large prostates, even >200 g. ^5,6

The HoLEP procedure consists of two main processes, enucleation followed by tissue morcellation. In recent years, there have been several studies examining various variables and techniques with the goal of improving efficiency and improving overall outcomes associated with the enucleation process. These have included laser fiber size and laser settings (power, frequency, and pulsed settings), and even use of thulium instead of holmium laser. ^{7 –9}

In comparison, there have been fewer studies investigating the morcellation process. Morcellators are often used with an offset nephroscope and have either reciprocating or oscillating blades. There are currently only three popular mechanical morcellators used throughout the world; the Wolf Piranha^®, Lumenis VersaCut, and Storz DrillCut ^® , in which the latter currently does not have FDA approval. There have been ex vivo and in vivo studies comparing the Wolf and Lumenis systems, including cost differences and surgeon/OR staff preference, and prospective data to compare the Lumenis and Storz systems. ^{10 –13}

To our knowledge, there has been no head-to-head comparison of the Wolf Piranha and Storz DrillCut morcellators. This multi-institutional retrospective study aims to evaluate the safety and efficacy of these two morcellators.

Materials and Methods

After Institutional Review Board approval, a multi-institutional retrospective chart review of prospectively collected data was performed at two institutions with a single surgeon at each center performing these procedures: HE at Thunder Bay Regional Health Sciences Center with the Storz DrillCut, and MET Baylor Scott and White Medical Center with the Wolf Piranha. Data were collected for the Storz cohort from October 2017 to October 2018 and was obtained for the Wolf cohort from August 2015 to June 2018.

Preoperative, perioperative, postoperative, and demographic data for both groups were analyzed and compared retrospectively. Protocol dictated that nursing staff would record start and stop times for each portion of the enucleation and morcellation procedures. Pathology and weight of specimens were recorded by standard hospital protocols for transurethral specimens. The cohort data were stored in a REDCAP database for secure data collection with password protection and only shared between institutions through secured webmail with nonidentifiable data. A Chi-square test (or Fisher's exact test when low cell counts were present) was used to test for associations in bivariate comparisons. A two-sample t-test (or Wilcoxon rank-sum test when appropriate) was used to test for differences in continuous variables between two groups.

Results

A total of 506 patients were collected in the Wolf cohort from August 2015 to June 2018 vs 60 patients from October 2017 to October 2018 for the Storz cohort. The average age was comparable for both cohorts, 71.6 vs 72.9 for the Wolf and the Storz, respectively (p = 0.51) (Table 1). Cardiovascular disease was noted in 368 patients and diabetes mellitus in 139 patients in the Wolf cohort. A total of 37 patients were identified with cardiovascular disease and 17 patients with diabetes mellitus in the Storz cohort.

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Table 1.

Preoperative Data

Intraoperative data were recorded (Table 2). The average enucleation time was 45.9 minutes for the Wolf cohort and 86.08 minutes for the Storz cohort (p < 0.0001). Morcellated pathologic weight was 52.3 g on the Wolf arm and 101.7 g on the Storz Arm (p < 0.0001). Weights were obtained by weighing chips postoperatively. Ultrasound, digital rectal exam, or CT scan was used for estimated gland size preoperatively. Due to variability of preoperative gland sizing, this was excluded from our final data set and pathologic weight used for comparison.

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Table 2.

Intraoperative Data

Average morcellation time was found to be longer in the Storz arm: 12.2 minutes in the Wolf arm and 17.5 minutes in the Storz arm (p < 0.0001). Overall, average morcellation rates were faster in the Storz arm. Morcellation rate was 5.8 g/min for Wolf and 6.7 g/min in the Storz (p = 0.0015). Morcellator malfunction was significantly lower in Wolf cohort 0% vs 6.6% in the Storz (p = 0.0001), but this did not significantly slow morcellator efficiency times (Table 3).

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Table 3.

Morcellator Malfunction and Injury

The total number of mucosal bladder injuries was comparable with rates of 1.4% and 1.6% in the Wolf and Storz groups, respectively (p = 0.59) (Table 3). One patient in the Wolf cohort required prolonged catheter placement for extraperitoneal extravasation of contrast following the procedure. However, no patients in either cohort required additional procedures or surgery related to mucosal injuries during morcellation. No bipolar resection or other method was required to remove morcellated prostate tissue.

Median hospital stay in both cohorts was <24 hours. Tissue pathology was examined for prostate cancer in both groups. A total of 14 patients in the Wolf cohort and 6 patients in the Storz cohort were noted to have Grade Group 1 or 2 prostate cancer (no Grade Group 3 or higher were noted). The average catheter duration was also <24 hours. Several patients in both cohorts failed voiding trials. However, at 1-week follow-up, 100% of the Storz cohort and 98.4% of Wolf Cohort patients had passed voiding trials with permissible postvoid residuals (PVRs) (did not require self-catheterization or Foley reinsertion).

At the time of data collection, PVRs had been recorded at a 3- to 6-month postoperative appointment for 33 patients in the Storz cohort with an average PVR of 54cc, whereas 85 patients in the Wolf cohort had an average of 62 cc.

Discussion

This is the largest in vivo comparison of the Wolf Piranha and Storz DrillCut prostate morcellation devices (PMDs) to date. Demographics between groups were similar, and despite numerous patients with multiple significant comorbidities, specifically cardiovascular disease and diabetes, patients showed good functional outcomes in terms of being able to void and appropriately empty their bladders. This was even seen in the setting of advance age (age >80–90), which is consistent with previous studies looking at elderly patients undergoing HoLEP. ¹⁴

Both PMDs had similar rates of morcellation with 6.66 vs 5.79 g/min in the Storz and Wolf arms, respectively. These values are similar to previously published data that showed morcellation rate of 6.46 g/min in the Storz Drillcut ¹⁵ and 5.60 g/min for the Wolf Piranha in a separate study. ¹¹ While there was a statistical difference between the two groups, resident surgeons were involved in the Wolf group, which could partially account for the slower rate of morcellation. Also, it is unclear how clinically significant this difference is even in the setting of very large prostates.

Malfunctions with the two PMDs were low with 0 reported malfunctions with the Piranha and a rate of 6.6% with the DrillCut (again with previously reported rates of 2.7% ¹¹ and 6.6%, ¹⁵ respectively) should be noted that, although the DrillCut had more reported malfunctions, typically due to obstruction of the morcellation blades, this did not seem to significantly affect the efficiency of the system. One explanation for this is that the average prostate volume morcellated was significantly larger in the DrillCut group (52.3 vs 101.7 g) and the associated morcellation times were expectedly longer (17.5 vs 12.2 minutes). These differences could increase the likelihood of morcellator malfunction.

Mucosal bladder injuries were rare and comparable between the Piranha and DrillCut, 1.4% and 1.6%, respectively, and only one patient required extended catheter use for a bladder injury. Overall postoperative outcomes were similar as well. Hospital stays were <24 hours as patients were observed overnight and underwent an active voiding on postoperative day 1.

In addition to the retrospective nature of this study, we do acknowledge some additional limitations. First, while both surgeons are well experienced in performing the HoLEP procedure, each surgeon only used one brand of morcellator. It is difficult to tell if there would be any differences if each facility used both morcellators. Next, there was a substantial difference in the two groups with regard to the size of the prostates treated. This is likely due to different practice patterns with regard to what patients undergo a HoLEP at each institution. As described earlier, it a may provide a source for the increased morcellator malfunctions in the Storz group.

Overall, this study shows slightly improved morcellation rate with the DrillCut morcellator, although this may not be clinically significant. Otherwise, the two PMDs are largely comparable. To our knowledge, there has not been a head-to-head study comparing all three available morcellators (Wolf Piranha, Storz DrillCut, and Lumenis VersaCut) at once, but with the addition of this study, these PMDs have now all been compared in vivo. A prospective randomized control trial comparing the DrillCut and VersaCut showed that the DrillCut has slightly slower rates of morcellation (3.6 vs 4.9 g/min). ¹³ However, similar to our study, this did not appear to be clinically significant as morcellation times (22.6 vs 17.3 minutes) were not statistically significant. Overall complications, including bladder injuries were similar. ¹³

Similarly, there have been studies comparing the Wolf Piranha and Lumenis VersaCut. ^{10 –12} Nonrandomized trials have shown conflicting data with regard to which morcellator is more efficient and both suggested the Piranha had a slightly better safety profile. ^10,12 However, existing prospective randomized trial showed similar morcellation rates and similar low complication rates (including mucosal bladder injuries) between the PMDs. ¹¹

There are some small differences between the three existing PMDs in independent studies. Combining our findings with existing data comparing PMDs, overall safety, efficiency, and reliability of the devices are arguably similar. Despite this, surgeon and OR staff preference appears to be variable. A few studies have looked at device preference between the Piranha and the VersaCut. In a single institution study, physicians preferred the Piranha while the OR staff preferred the VersaCut as it was easier to trouble shoot. ¹¹ However, in a more widespread survey, 58% of physicians preferred the VersaCut while 42% preferred the Piranha. ¹⁶ In both cases, the primary driving forces behind morcellator preference was perceived efficiency, safety, and ease of use of the device and less so, cost of the devices. ^11,16 It is not unreasonable to believe these motivators would be similar if the DrillCut was also evaluated. Preference may also come down to with what device physicians are trained.

Conclusions

In this largest retrospective study, to date, comparing the Wolf Piranha and Storz DrillCut morcellators, the Storz DrillCut had higher efficacy in morcellation when compared with Wolf Piranha. However, it was associated with more malfunctions. The two morcellators have statistically similar safety profiles. When extrapolating this new information with existing studies comparing the available morcellators on the market (including the Lumenis VersaCut), all three arguably performed similarly with comparable complication rates. Selecting a morcellator may come down to physician and OR staff preference as well as the cost analysis, although additional prospective trials comparing all three together may provide further elucidation.