Abstract
Introduction:
The FlexStone device (EndoTheia, Nashville, TN) is an investigational, steerable stone basket. The device provides additional flexion separate from the ureteroscope without an assistant. We evaluated the safety and feasibility of this new novel device for stone retrieval.
Patients and Methods:
In this first-in-human clinical trial, 10 patients underwent flexible ureteroscopy (URS) for renal calculi using the FlexStone device. The primary endpoint was the safe and successful basketing of renal stones with the device. Intraoperative and short-term postoperative adverse events were evaluated. Secondary endpoints included surgeon workload assessed by the National Aeronautics and Space Administration Task Load Index (NASA-TLX).
Outcomes:
The majority of patients had a solitary stone (60%) and stone was in the lower pole (90%) with a minority of patients also having stones in upper pole (20%) or interpolar region (10%). Median cumulative axial stone size was 11 mm (interquartile range [IQR]: 7.5–15.25 mm). The device was used to extract (60%) or reposition (40%) of stones. Surgeons used the FlexStone device to successfully basket target stones in 9 cases (90%). No intraoperative complications occurred. Postoperatively, one patient needed a second URS procedure for hydronephrosis, but no obstructing stone was seen. On the NASA-TLX scale from 1 (low) to 21 (high), the demand when using the device was low, with median mental demand—6 (IQR: 4–12), physical demand—9 (IQR: 6–12), temporal demand—6 (IQR: 4–6), and frustration—6 (IQR: 1–6). Surgeons rated the device with high overall performance (median 3, IQR: 3–8, perfect = 1).
Conclusion:
Our preliminary investigation demonstrates the safety of a new, unique steerable stone basket. The FlexStone device is a potentially valuable addition to the urologist’s armamentarium, especially for complex caliceal anatomy and improving ergonomics when using URS.
Keywords
Introduction
Flexible ureteroscopy (URS) has gained significant popularity globally among both urologists and patients.1,2 The procedure is minimally invasive with favorable complication and stone clearance rates as compared with other stone treatment modalities.3,4 Because of the ongoing increase in incidence of kidney stone disease, the number of URS performed has increased by 130% in the past decade in the United States, with similar trends seen globally. 5
The efficiency of URS is dependent upon the surgeon’s ability to manipulate the ureteroscope and subsequently the laser and/or stone basket to reach all stones. New and improved endoscopic instruments and lasers have expanded the role of URS for increasing stone volume and anatomical complexities. 6 Calices at acute angles, especially in the lower pole of the kidney, present unique anatomical challenges where the ureteroscope must undergo an average 140° bend from the ureter to access the stone, which restricts the ureteroscope maneuverability and hinders stone treatment or removal.7–9
We assessed a novel flexible, steerable stone basket (i.e., EndoTheia FlexStone device) for stone extraction and repositioning during URS. Specifically, we evaluated device safety, feasibility, and surgeon experience with the FlexStone device in a prospective, first-in-human clinical trial.
Discussion of Technology
An investigational device has been specifically designed to address the challenge of capturing stones in hard-to-reach angles. The FlexStone device (EndoTheia, Nashville, TN has the following features: (1) tipless basket, (2) steerable tip with bidirectional deflection up to 90 degrees independent of the flexion of the ureteroscope, (3) flexible transmission shaft, and (4) ergonomic user interface (Fig. 1A). The steerable tip gives the physician an additional 90 degrees of controllable deflection (Fig. 1B).
During URS, the 2.1 F high-torque flexible transmission shaft is delivered through the working channel of a standard flexible ureteroscope. The tip deflection, rotation, insertion/retraction, and the opening and closing of the basket are controlled using an ergonomic handle, which can be used without the need for an assistant.
Patients and Methods
After obtaining institutional review board approval from Vanderbilt University Medical Center (IRB#231189), 10 patients undergoing URS at our institution were recruited for this study. Inclusion criteria included adult patients (age ≥ 18 years old) with renal stones who were appropriate candidates for URS according to American Urologic Association guidelines. 10 Individuals were excluded if pregnant, currently undergoing any treatment for malignancy, active urinary tract infection, complex anatomy that precludes retrograde access to the ureter or kidney, or unable/unwilling to provide informed consent.
Demographic and stone characteristics were recorded for each participant using a chart review. Demographic information recorded included age at time of URS, gender, and body mass index (BMI). We extracted stone characteristics based on preoperative computed tomography (CT) scans.
URS was performed for renal stone treatment using standard clinical practice, using pressurized irrigation with the Thermedx FluidSmart Fluid management system (Stryker, Portage, MI) with holmium laser lithotripsy and/or basket extraction of stones, and discretion of the endourologist. Stones within a calix, including those attached to the papilla, were treated with laser. FlexStone was used as a primary basket. Placement of a ureteral access sheath or a ureteral stent was placed if considered necessary by the surgeon. Intraoperative videos were recorded during FlexStone basket use.
The primary endpoint was the safe and successful basketing of renal stones with the device. Intraoperative and postoperative adverse events and residual stones on standard postoperative imaging [renal ultrasonography or CT] were evaluated. Stone free was defined as having no detectable residual stone fragments.
The secondary endpoint was the workload associated with using the FlexStone basket. Surgeons reported the workload within 24 hours after surgery using the National Aeronautics and Space Administration Task Load Index (NASA-TLX), a validated questionnaire to assess perceived workload for the trial completed across six subscales: mental demand, physical demand, temporal demand, effort, performance, and frustration level on a 21-point scale.11–13 Surgeons were also asked to rate the ability to aim the basket and the basket’s actuation.
Results
The study included six male patients and four female patients with a median age of 61 years (interquartile range [IQR]: 57–68 years) and BMI of 31 kg/m2 (IQR: 26–38 kg/m2; Table 1). Six patients (60%) had at least one or more prior symptomatic stone episodes. On preoperative CT scan, most patients had solitary stone (60%) located in the lower pole (90%). A minority of patients also had stones in upper pole (20%) or interpolar region (10%). Median cumulative axial stone size was 11 mm (IQR: 7.5–15.25 mm). A variety of stone densities were seen; median stone Hounsfield units were 564 (IQR: 462–735).
Clinical, Stone, and Intraoperative Characteristics
More than one location selected if 1+ stone on preoperative imaging.
ASA = American Society of Anesthesiologists; F = French; HU = Hounsfield units; IQR = interquartile range; N = number.
The FlexStone device was used to extract (60%) or reposition (40%) stones. An assistant was optional and not needed to actuate the basket for any stone manipulation. FlexStone device was able to successfully basket 9 out of 10 target stones including stones in anterior or lower pole calices or soft matrix stones. In Figure 2, we demonstrate the utility of the FlexStone device in extracting a stone attached to papilla in an anterior calix. As the corner of the infundibulum blocked the basket from accessing the stone, a standard tipless basket was unable to grasp the stone. However, the stone was able to be reached with FlexStone device. In one case, the surgeon converted to a traditional basket when an infundibulum was too narrow to allow for articulation of the FlexStone device.
We were able to basket stones of variable densities including soft matrix stones (median HU 564, IQR: 462–735). Stones were held within the basket while withdrawing the scope down the ureter or ureteral access sheath without dropping any stones, comparable to existing commercial stone baskets. Stone remained contained within the basket without an assistant holding the basket closed.
No intraoperative complications were seen from the use of the FlexStone device. Postoperatively, one patient needed repeat URS for hydronephrosis in the absence of stent, but no obstructing stone or lesion was seen. The hydronephrosis resolved spontaneously on subsequent follow-up imaging.
On the TLX scale from 1 (low) to 21 (high), the demand when using the device was low with median mental demand 6 (IQR: 4–12), physical demand 9 (IQR: 6–12), temporal demand 6 (IQR: 4–6) and frustration 6 (IQR: 1–6; Fig. 3). The device was also rated with high overall performance (median 3, IQR: 3–8, perfect = 1).
NASA-TLX and FlexStone device performance. NASA-TLX = National Aeronautics and Space Administration Task Load Index.
At a median of 50 days postoperatively (IQR: 32–64 days), 70% of patients were stone free. Stone-free status was assessed using renal ultrasonography in 7 patients (70%) and CT in 2 patients (20%).
Discussion
We report the first human clinical trial with the FlexStone device, a steerable basket to access stones in challenging locations. Our initial experience shows that the FlexStone device is safe to access stones during URS with low workload.
There were no intraoperative complications related to the use of the basket with or without ureteral access sheath. Though there was one patient with postoperative ipsilateral hydronephrosis, repeat URS revealed no obstructing stone or lesion. The hydronephrosis resolved spontaneously on follow-up imaging. This is within the known risk of postoperative hydronephrosis after URS and was likely unattributed to the FlexStone device. 14 The learning curve for the device was minimal, typically just minutes. The device is easily adopted into use after minimal instruction on controls in the handpiece. The basket handpiece was designed for use by the surgeon alone and does not require an assistant for basketing. Stones were of variable densities (Hounsfield unit range 242–1164), including soft matrix stones, and could be collected by basket.
The FlexStone device is a promising tool in the urologist’s armamentarium for complex URS. The ability to angle the FlexStone basket independently of the ureteroscope can be beneficial to access stones in unfavorable locations. One stone attached to an anterior papilla was unable to be reached with a standard basket but was easily reached with FlexStone basket (Fig. 2). Furthermore, the lower pole is a common site for basketing as displacement of lower pole stones to other calices results in a significantly higher stone-free status. 15 We were able to basket 9 stones (100%) in the lower pole.
Workload via NASA-TLX with the FlexStone basket (6–9) was similar to other commercially available baskets. Schlager et al. reported overall low workload scores (7–9) when using the NCircle® tipless basket (Cook Medical LLC, Bloomington, IN) with a standard reusable ureteroscope. 16 Ventimiglia et al. reported similar very low workload scores (6–8) and a favorable overall effort score with a ZeroTipTM basket with LithoVue EmpowerTM (Boston Scientific, Marlborough, MA), which is also designed for basketing without the need for an assistant. 17
The FlexStone device may also improve surgeon ergonomics. With increased use of URS with higher stone volume, longer operative times result in prolonged standing and static postures. This, coupled with the contortion of the surgeon to access stones in unfavorable caliceal angles, can cause significant strain on muscles of the wrist and thumb while holding the scope. There is a direct relation between the time of the surgery and the development of muscular fatigue with decrease in the muscular performance in endourological surgeries with potentially negative consequences on the surgeon and the outcome of the surgery. 18 Elkoushy et al. reported that the prevalence of orthopedic complaints among endourologists was 64% including hand problems (17%). This risk is higher in older endourologists (>40 years), longer duration of practice (>10 years), and annual caseload of longer duration procedures. 19 To minimize workplace injury and preserve career longevity, ergonomics in the operating room has become a growing field of interest. The FlexStone device was designed as a tool to aid with this ergonomic challenge and expand the limits of current URS for stone management.
Although this study provides valuable insights into the use of the FlexStone device, there are several limitations. First, the data were collected from a single academic institution in a small sample size, which may limit generalization widely. Second, the quantitative analysis of this study focused on the safety and ability to capture stones. FlexStone device was not compared directly with other similar baskets. Future studies are needed to evaluate the clinical benefit of the FlexStone device compared with traditional baskets. Additionally, we plan on evaluating FlexStone performance at different pelvicaliceal angles and assessing intrarenal pressures when using the device. Although this study is only a feasibility study, it is our hope that once approved by the Food and Drug Administration, the investigational device used in this study will ultimately lead to an increase in the overall stone-free rates and a decrease in the total procedure duration by enabling urologists to better access and the ability to capture kidney stones.
Conclusion
Our preliminary investigation demonstrates the safety and feasibility of a new, unique steerable stone basket. Further investigation is needed, but the FlexStone device is a potentially valuable addition to the urologist’s armamentarium, especially for complex caliceal anatomy.
Authors’ Contributions
K.A.M.: Investigation, data curation, formal analysis, writing original draft, writing review and editing, visualization. A.I.K.: Investigation, data curation, writing review and editing, visualization. R.S.H.: Conceptualization, methodology, investigation, resources, writing review and editing, visualization, supervision. N.L.K.: Conceptualization, methodology, investigation, resources, writing review and editing, visualization, supervision.
Footnotes
Author Disclosure Statement
No competing financial interests exist.
Funding Information
EndoTheia provided FlexStone devices for the study. Sponsors were not involved in study design, data collection, analysis, and interpretation, in the report’s writing, or in the decision to submit the article for publication.