A Novel Flexible Ureteroscope with Omnidirectional Bending Tip Using Joystick-Type Control Unit (URF-Y0016): Initial Validation Study in Bench Models

Abstract

Purpose:

The conventional flexible ureteroscope has limited access into the lower calix and often causes biomechanical stress to surgeons. Recently, a novel flexible ureteroscope with an omnidirectional bending tip with a joystick-type control unit (URF-Y0016; Olympus, Japan) was developed. We verified the operability and ergonomics of the URF-Y0016 compared with that of the conventional flexible ureteroscope (URF-P6) in bench models.

Materials and Methods:

Twenty-five medical students with no experience in performing ureteroscopic manipulation were randomly assigned to URF-Y0016 and URF-P6 leading groups in a crossover study. The task was performed using a simple model as an exploratory experiment and an artificial kidney model as an evaluation experiment. We compared the task completion times of both groups, while the factors influencing task completion time were entered into a multivariate model. The ergonomics of endourology were compared using a validated questionnaire.

Results:

The task completion time in the URF-Y0016 group was significantly shorter than in the URF-P6 group (p < 0.001). The URF-Y0016 group showed no difference in task completion time between each renal calix, whereas in the URF-P6 group the task completion time in the lower calix was significantly longer than that in other calices (p < 0.001). In multivariate analysis, the model of flexible ureteroscope used significantly influenced the task completion time (p < 0.001). The ergonomics of the URF-Y0016 group were significantly better than those of the URF-P6 group (p = 0.001).

Conclusions:

URF-Y0016 may offer benefits in ureteroscopy performance over the conventional flexible ureteroscope.

Introduction

Renal stone disease is common and its prevalence increased from 5.2% in 1988–1994 to 8.8% in 2007–2010 in the United States.¹ Similarly, in Japan, the annual incidence (per 100,000) of first-episode upper urinary tract stones increased from 68.9 in 1995 to 107.8 in 2015.² The incidence of intervention for asymptomatic renal stones has been reported to be 7% to 26%.³ Owing to recent advances in flexible ureteroscopes, ureteroscopy (URS) has become a widely used technique for the surgical intervention of renal stones. The Current European Association of Urology (EAU) guidelines recommend URS as an option for the treatment of all renal calculi.⁴ However, the management of lower pole renal calculi is more demanding than the treatment of other renal calculi because of the associated inherent anatomical challenges. The conventional flexible ureteroscope's control mechanism, operated in two deflected directions, is particularly difficult to maneuver in the lower pole of the kidney. Therefore, to improve operability, a novel flexible ureteroscope with an omnidirectional bending tip that uses a joystick control unit (URF-Y0016; Olympus, Japan) was developed. Herein, we verified the operability of URF-Y0016 compared with the conventional flexible ureteroscope in bench models.

Materials and Methods

Development of the device

The handle of URF-Y0016 consists of a handgun-type gripping part and a joystick-type control unit for bending the tip (Fig. 1A). The specifications of URF-Y0016 are shown in Figure 1B. The bending range of the ureteroscopic tip is 275° upward and downward and 100° to the left and right. The ureteroscopic tip can be omnidirectionally bent using the joystick-type control unit.

FIG. 1.

(A, B) Armamentarium of a novel flexible ureteroscope (URF-Y0016). The handling image of a handgun-type gripping part with a joystick-type control unit (A). Specifications of URF-Y0016 (B).

Participants

Twenty-five inexperienced with ureteroscopic manipulation medical students (15 men and 10 women) were recruited on a voluntary basis to verify the operability of URF-Y0016 and URF-P6 (Olympus, Japan). Participants were randomly assigned to the URF-Y0016 group (n = 13) and the URF-P6 group (n = 12) in a crossover study (Fig. 2). All participants provided written informed consent, and the Faculty of Medicine Research Ethics Committee, Kyorin University, approved the study.

FIG. 2.

Study design of initial validation for URF-Y0016.

Experimental evaluation

The participants were introduced to the devices through a theoretical lesson and a video with demonstration of the manipulation of ureteroscopes in bench models before each task. An exploratory experiment was performed using a simple model with numbered targets ranging from 1 to 9 and a neutral target in the center (Fig. 3A). In the exploratory experiment, the basket forceps (Flex-Catch NT 1.9Fr, Olympus, Japan) were inserted into the working channel and made contact with the numbered targets as well as with the neutral target before and after making contact with each numbered target. An evaluation experiment was performed using an artificial kidney model on a Smart Simulator.⁵ Three target pins were placed at the anterior, medial, and posterior of each renal calix, for a total of nine targets (Fig. 3B). The task began when the ureteroscope was positioned into the ureter access sheath and inserted into the ureter, after insertion of the ureteroscope into each renal calix to perform the calix task. The calix task consisted of touching the medial, anterior, and posterior pins in the renal calix using the basket forceps in the aforementioned order through the working channel. The calix task was completed when the ureteroscope was returned to the ureter access sheath. The whole task finished when all renal calices were completed. Each experiment was performed three times, and the task completion time of the third experiment was used for evaluation. The average value of the completion time of the preceding and succeeding tasks was evaluated to eliminate potential bias.

FIG. 3.

(A, B) Bench models used in this study. Simple model in exploratory experiment (A), and kidney model in evaluation experiment (B).

We measured the hand size (hand length, hand breadth, thumb length, and middle finger length) and the grip strength to evaluate the possible effects on endoscopic handling. In addition, a self-completed questionnaire was administered to the responders asking them about their participation in sports or video games. In the self-completed questionnaire, the subjects were asked to choose a response whether they participated in sports and/or video games, with the following response options: strongly agree, agree, disagree, and strongly disagree. The frequency of participating in sports and/or playing video games was established by choosing one from the following four responses: very often, often, sometimes, rarely/never.

Evaluation of ergonomics

The evaluation of ergonomics was performed using a validated questionnaire regarding robotic flexible URS.⁶ The questionnaire was administered and filled in before and after each task. Ergonomics were evaluated using the difference between the average post- and pre-task value.

Statistical analysis

Data are provided as median and interquartile range (IQR). We performed a univariate analysis using both the Mann–Whitney U test and Spearman's rank correlation coefficient analysis. A multivariate analysis was performed using a stepwise multiple linear regression analysis. We chose a probability level of 0.05 for statistical significance. Statistical analyses were conducted using the SPSS software (version 18.0; IBM Corp., Armonk, NY).

Results

The median (IQR) age of the subjects was 25 (+2) years. The overall median (IQR) height was 167.0 (+16.0) cm; men 172.0 (+8.0) cm and women 153.5 (+11.0) cm. The median (IQR) hand length, hand breadth, thumb length, and middle finger length were 175.0 (+19.0) mm, 78.6 (+9.2) mm, 58.8 (+8.9) mm, and 73.5 (+8.4) mm, respectively. These are standard values for healthy Japanese adults.⁷ The median (IQR) grip strength was 38.5 (+18.0) kg. Sixteen (64%) and 20 (80%) responders answered “strongly agree” and “agree” to sport and video-game participation, respectively. Thirteen (52%) and 18 (72%) responders answered “very often” and “often” to the frequency of sports and video-game participation, respectively.

The task completion time using URF-Y0016 was significantly shorter than that using the URF-P6 (82.0 vs 207.0 seconds, p < 0.001) (Fig. 4). Moreover, in each calix task, the completion time in the URF-Y0016 group was significantly shorter than the one in the URF-P6 group in all calices (Table 1; p < 0.001). There was no significant difference in the task completion time between each calix in the URF-Y0016 group, but in the URF-P6 group the task completion time in the lower calix was significantly longer than that in the upper and middle calices (Fig. 5; p < 0.001). The task completion time was correlated with the model of the ureteroscope (Table 2; r = −0.839, p < 0.001). In multivariate analysis, the model of the ureteroscope was a significant influencing factor for task completion time (Table 3; p < 0.001).

FIG. 4.

Comparison of task completion time between URF-Y0016 and URF-P6.

FIG. 5.

The task completion time of URF-Y0016 and URF-P6 in each renal calix.

Table 1.

Comparison of Task Completion Time in URF-P6 and URF-Y0016

		URF-P6	URF-Y0016	p
Upper calix	Task completion time (seconds)
	1st	70.0 (39.0)	34.0 (15.0)	<0.001
	2nd	64.0 (25.0)	27.0 (12.0)	<0.001
	3rd	54.0 (26.5)	26.0 (11.0)	<0.001
Middle calix	Task completion time (seconds)
	1st	66.0 (41.0)	38.0 (24.0)	0.001
	2nd	53.0 (37.0)	28.0 (19.0)	0.004
	3rd	48.0 (17.5)	24.0 (12.0)	<0.001
Lower calix	Task completion time (seconds)
	1st	208.0 (147.0)	46.0 (48.0)	<0.001
	2nd	118.0 (137.0)	31.0 (23.0)	<0.001
	3rd	98.0 (121.5)	26.0 (23.0)	<0.001
Total	Task completion time (seconds)
	1st	344.0 (237.0)	118.0 (93.0)	<0.001
	2nd	237.0 (131.0)	89.0 (54.0)	<0.001
	3rd	207.0 (122.0)	82.0 (49.0)	<0.001

Data are provided as the median value (IQR).

IQR = interquartile range.

Table 2.

Correlation Between Factors and Task Completion Time

Factors	Correlation coefficient	p
Model of ureteroscope	−0.839	<0.001
Gender	0.127	0.378
Age	−0.126	0.384
Body height	0.032	0.825
Length of hand	0.010	0.946
Length of thumb	0.006	0.967
Length of middle finger	0.065	0.656
Breadth of hand	−0.047	0.746
Grip strength	−0.043	0.766
Sporty person	−0.017	0.908
Frequency of engaging in sports	−0.031	0.829
Video gamer	0.142	0.325
Frequency of playing video games	0.208	0.148

Table 3.

Influencing Factors for Task Completion Time by Stepwise Multiple Linear Regression Model

Factors	Standardized coefficient	p
Model of ureteroscope	−0.639	<0.001
Gender	0.042	0.707
Age	−0.148	0.185
Body height	0.115	0.307
Length of hand	0.070	0.533
Length of thumb	0.120	0.286
Length of middle finger	0.155	0.166
Breadth of hand	−0.061	0.588
Grip strength	−0.033	0.768
Sporty person	−0.009	0.936
Frequency of engaging in sports	−0.155	0.164
Video gamer	0.206	0.062
Frequency of playing video games	0.164	0.140

The ergonomics of URF-Y0016 according to the validated questionnaire were significantly better than those of URF-P6 (5.0 vs 13.0, p = 0.001). The URF-Y0016 group reported less arm pain, forearm pain, hand pain, wrist stiffness, and finger numbness than the URF-P6 group (Table 4; p = 0.018, p = 0.008, p = 0.011, p = 0.011, and p = 0.001, respectively).

Table 4.

Comparison of Ergonomics of Endourology Using a Validated Questionnaire in URF-P6 and URF-Y0016

Variables	URF-P6	URF-Y0016	p
Musculoskeletal pain	1.0 (1.0)	0.0 (1.0)	0.426
Neck pain	0.0 (1.0)	0.0 (1.0)	0.143
Shoulder stiffness	1.0 (1.5)	0.0 (1.0)	0.118
Arm pain	2.0 (2.0)	1.0 (1.0)	0.018
Forearm pain	2.0 (1.5)	0.0 (1.0)	0.008
Elbow stiffness	0.0 (1.0)	0.0 (1.0)	0.963
Hand pain	2.0 (2.0)	1.0 (2.0)	0.011
Wrist stiffness	2.0 (2.5)	0.0 (1.0)	0.011
Finger numbness	2.0 (2.0)	1.0 (2.0)	0.001
Back pain	0.0 (0.5)	0.0 (0.0)	0.113
Leg pain	0.0 (0.0)	0.0 (0.0)	0.393
Eye strain	1.0 (2.0)	1.0 (1.5)	0.414
Total	13.0 (10.5)	5.0 (8.5)	0.001

Data are provided as the median value (IQR).

Discussion

We conducted the initial validation of URF-Y0016 using an artificial kidney model and showed, through a validated questionnaire, that the operability and ergonomics of URF-Y0016 were superior to those of URF-P6 in bench models.

With the development of endoscope miniaturization, deflection technology, optical quality, and auxiliary devices, retrograde intrarenal surgery (RIRS) using a flexible ureteroscope has become a useful option in the treatment of renal stones. However, the control mechanism in conventional ureteroscopes makes them particularly difficult to maneuver in the lower pole of the kidney. During RIRS for lower pole renal stones, it is often necessary to tightly deflect and rotate the tip of the ureteroscope and hold it during the entire procedure. Consequently, Healy and colleagues reported that hand and wrist problems including paresthesia and musculoskeletal pain appeared in 32% of endourologists.⁸

URF-Y0016 utilizes a handgun-type handle, which can deflect its tip in all directions using its joystick-type control unit. It allows intuitive operability and sufficient movement of the ureteroscope, with less hand and wrist movements than the conventional ureteroscope. An ex-vivo study of a flexible colonoscope showed that a handheld controller with a thumb joystick as an intuitive user interface improved efficiency in tip steering and increased user preference.⁹ In this study, URF-Y0016 significantly reduced arm, forearm, and hand pain, wrist stiffness, and finger numbness according to the validated questionnaire, as compared with the URF-P6 in bench models. RIRS using URF-Y0016 may improve the ergonomics of endourologists.

Another notable finding of this study was that URF-Y0016 showed no significant difference in task completion time between each renal calix. Stones located in the lower-anterior minor calix had a negative impact on stone-free status in RIRS using the conventional ureteroscope.¹⁰ The URF-P6's task completion time of the lower calix was significantly longer than that of other renal calices. The URF-P6 had difficulty in reaching the target pin located at the lower-anterior calix, which affects the task completion time of the lower calix.

Several studies demonstrated the effects of hand size or being a video gamer on endoscopic skills. A survey of 726 laparoscopic surgeons showed that hand size was a significant contributing factor to the difficulty in using laparoscopic instruments. Many surgeons with small hands, especially female surgeons, have experienced difficulties with laparoscopic instruments.¹¹ In addition, an ex-vivo study with 40 medical officers showed that playing video games improved the baseline performance in laparoscopic simulator skills.¹² Laparoscopic surgery and endourology require visual-spatial skills and hand-eye coordination, which are similar to the skills needed for video gaming. However, our results showed that hand size and experience with video games were not correlated with the task completion time.

There were several limitations in this study. First, this study included off-label information and was conducted to evaluate new technologies and the potential future use of this device. Second, this initial validation study of URF-Y0016 was performed in comparison with the commonly used conventional ureteroscope URF-P6; however, the type of ureteroscope used may affect the ergonomics of flexible URS.¹³ Further validation using single-use and/or multiple-use digital ureteroscopes may confirm the usefulness of URF-Y0016 ergonomics. Third, this study was performed using an artificial kidney model on Smart Simulator. Pelvicaliceal morphology has an impact on the operability of flexible ureteroscopes. To minimize the influence of morphology, this pelvicaliceal system was designed based on the short infundibular length (≤15 mm) and wide infundibular width (≥10 mm) of each calix, and the wide infudibulopelvic angle (>40°) in the lower calix.¹⁴ Finally, we recruited medical students with no experience of ureteroscopic manipulation to eliminate the bias of URS experience. Large studies are required to investigate the clinical application of URF-Y0016.

Conclusions

The URF-Y0016, a novel flexible ureteroscope with an omnidirectional bending tip using a joystick-type control unit, may improve the operability and ergonomics of flexible URS.

Footnotes

Acknowledgment

We thank Editage (www.editage.com) for English language editing.

Author Disclosure Statement

No competing financial interests exist.

Funding Information

Olympus, Japan, funded and lent the equipment used in this study.

Abbreviations Used

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