Learning curve of semi-rigid ureteroscopy for small calculi: how many cases are necessary?

ABSTRACT Introduction: semi-rigid ureteroscopy is the procedure of choice for the treatment of ureterolithiasis, but it requires a learning curve to be performed safely. Objective: To describe an estimate of the learning curve for performing semi-rigid ureterorenolithotripsy in patients with small-sized ureterolithiasis and to estimate the minimum number of procedures necessary to safely perform the surgical procedure. Methods: this is a prospective study evaluating the learning curve of a resident of urology in the first 60 semirigid ureteroscopies in patients with ureterolithiasis up to 1cm. The patients were divided into three groups: Group I one to twenty surgeries, Group II twenty one to forty surgeries and Group III forty one to sixty surgeries. The surgeries were recorded and analyzed by two urologists experienced in endourology. A qualitative analysis was performed based on a previously validated tool and a quantitative analysis. Results: all qualitative variables had significant variation between Groups I and II (p<0.001), and between Groups I and III (p<0.001). There was a difference in time to access the ureter, passage of a double J catheter and total operative time between Groups I and II (p<0.001) and Groups I and III (p<0.001). Conclusion: after 40 cases there seems to be little increase in both quantitative as well as qualitative evaluation in surgical performance for performing semi-rigid ureterolithotripsy safely in calculations up to 1cm.


INTRODUCTION
T he first ureteroscopy was described in 1912 by Young and McKay, when a pediatric cystoscope was inadvertently inserted into the renal pelvis of a child with a dilated ureter, this finding being published in 1929 1 .
Ureteroscopy was introduced into clinical practice in the 1980s, when the first ureteroscope was produced by the urologist Perez-Castro in association with Karl Storz.The first semi-rigid ureteroscope was introduced into clinical practice in 1989, replacing the rigid model, as it allows flexion of the vertical axis without image distortion 1,2 .
It is a diagnostic and therapeutic procedure for urolithiasis, ureteral stenosis, and ureteral neoplasms 1,3 .Ureterolithiasis is the most common clinical condition requiring treatment with ureteroscopy 4 .
Ureterolithiasis can be treated with endoscopic surgery.The miniaturization of ureteroscopes associated with the introduction of the homium laser (Ho:YAG) improved stone-free rates and decreased complications resulting from the surgical procedure.Most calculi can be disintegrated with the laser and the holmium energy is completely absorbed by the water within five millimeters, ureter injuries being rare 5,6 .
The learning curve of semi-rigid ureteroscopy is not well described, especially for small calculi.The minimum number of cases to perform this procedure safely is still uncertain 4,[7][8][9][10][11] .

Original article A B S T R A C T A B S T R A C T
Introduction: semi-rigid ureteroscopy is the procedure of choice for the treatment of ureterolithiasis, but it requires a learning curve to be performed safely.Objective: To describe an estimate of the learning curve for performing semi-rigid ureterorenolithotripsy in patients with small-sized ureterolithiasis and to estimate the minimum number of procedures necessary to safely perform the surgical procedure.
Methods: this is a prospective study evaluating the learning curve of a resident of urology in the first 60 semirigid ureteroscopies in patients with ureterolithiasis up to 1cm.The patients were divided into three groups: Group I one to twenty surgeries, Group II twenty one to forty surgeries and Group III forty one to sixty surgeries.The surgeries were recorded and analyzed by two urologists experienced in endourology.A qualitative analysis was performed based on a previously validated tool and a quantitative analysis.Results: all qualitative variables had significant variation between Groups I and II (p<0.001), and between Groups I and III (p<0.001).There was a difference in time to access the ureter, passage of a double J catheter and total operative time between Groups I and II (p<0.001) and Groups I and III (p<0.001).Conclusion: after 40 cases there seems to be little increase in both quantitative as well as qualitative evaluation in surgical performance for performing semi-rigid ureterolithotripsy safely in calculations up to 1cm.Keywords: Learning Curve.Ureteroscopy.Ureteral Calculi.Urologic Surgical Procedures.Internship and Residency.
where we evaluated the learning curve of a resident in his first 60 semi-rigid ureteroscopies in patients with ureterolithiasis.The surgeries were recorded and analyzed by two urologists experienced in endourology.We also performed: a qualitative analysis based on a tool previously published in the medical literature by Vassiliou et al (Table 1), which consists of five parameters: tissue management, bimanual dexterity, depth perception, autonomy, and efficiency; and a quantitative analysis, based on surgical times for accessing the ureter, calculi treatment, double-J catheter insertion, and surgical time 12 .
This study had the participation of 60 patients, 35 male and 25 female, and the surgeries performed were divided into three groups: from the first to the twentieth surgery (Group I), from the twenty-first to the fortieth procedure (Group II), and from the forty-first to sixtieth surgery (Group III).
Indications for semi-rigid ureteroscopy were ureterolithiasis with persistent pain, failure of clinical management with tamsulosin, and patient choice for surgical treatment.We excluded patients with ureterolithiasis associated with urinary tract infection and cases in which the calculus migrated to the kidney during intervention.
All procedures were performed with patients under spinal anesthesia, in lithotomy position.The ureteroscope was introduced through the urethra, a cystoscopy was performed to identify the ureteral meatus, a 0.035mmx150cm hydrophilic guide wire was inserted through the ureteral meatus towards the renal pelvis, and its placement was confirmed by radioscopy.Ureteroscopy was performed with calculus identification and a tipless nitinol calculus extractor was passed and positioned before the calculus to prevent migration to the kidney.The calculus was fragmented with a 200 micrometer laser fiber with a power of 10 watts, the residual fragments being removed with the calculus extractor.A 4.8 Fr x 20-26cm double J catheter was inserted at the end of the surgery.
All procedures were performed with radioscopy and were 3. Able to complete task safely with moderate guidance 4.

Able to complete tasks independently without guidance.
a 2= middle ground between degrees 1 and 3; b 4 = middle ground between degrees 3 and 5.  recorded for further analysis.We collected demographic data and calculus size and location, and followed all patients for at least four weeks after double J catheter removal.
We evaluated the normally of continuous variables with the Kolmogorov-Smirnov test.Normally

RESULTS
The mean age of patients was 39±13.7 years, with 35 (58.4%) males and 25 (41.6%)females.There was no statistical difference in the size, location, and laterality of the calculi between groups: 4.7±1.62x 5.76±3.49x 5.42±2.27(p=0.37,groups I, II and III, respectively) (Table 2).All qualitative variables had significant variation between Groups I and II (p<0.001), as well as between Groups I and III (p<0.001).There was no statistical difference between Groups II and III in any qualitative variable (Table 3).There was no difference in time for calculus treatment between groups (p=0.14).There was a difference in the time for ureter access, double J catheter passage, and total operative time between Groups I and II (p<0.001), between Groups I and III (p<0.001), and there was no difference between groups II and III (Table 4).There were no intraoperative complications.Two patients in group I displayed intolerance to the double J catheter.

DISCUSSION
In our study, we observed a statistically significant difference between groups I and II (p<0.001) in the qualitative analysis that assessed tissue handling, bimanual dexterity, autonomy, depth perception, and efficiency, but when comparing groups II and III, there is no such difference.In the quantitative analysis, which evaluates the time of access to the ureter, treatment of   Currently, there are few prospective studies addressing the learning curve in endourological calculus treatment procedures and none focused on the learning curve for semi-rigid ureteroscopy 13 .
The main limitation in our work is the number of surgeons evaluated.On the other hand, several previously published articles evaluated the learning curve of a single surgeon, with very valuable and interesting results [14][15][16] .
Studies on the learning curve are extremely important to design the training of resident physicians in residency and fellowship programs to safely perform surgical procedures and better train surgeons.

CONCLUSION
After 40 cases, there seems to be little increase in both the quantitative and qualitative assessments of surgical performance.Thus, 40 cases seem to be enough for a surgeon to safely perform a semi-rigid endoscopic ureterolithotripsy on calculi of up to 1cm.

R E S U M O R E S U M O
This is a prospective study approved by the Ethics and Research Committee of our institution, carried out in a hospital with a urology residency program, 1 -Hospital Alemão Oswaldo Cruz, Centro Especializado em Urologia -São Paulo -SP -Brasil 2 -Faculdade de Medicina da Universidade de São Paulo, Departamento de Técnica Cirúrgica e Cirurgia Experimental -São Paulo -SP -Brasil 3 -Universidade de São Paulo, Hospital Universitário -São Paulo -SP -Brasil distributed variables were analyzed by two-tailed Student's t test or ANOVA.After ANOVA, we performed the Tukey's post-test for intergroup comparison.Variables that did not show a normal distribution were analyzed using the Mann-Whitney test.Qualitative variables were compared using the Mann-Whitney test.We analyzed categorical variables using the chi-square or Fisher's exact test.The significance level in this study was 5%.The software used was StatPlus® v. 2009 for Mac.

Table 1 -
Global rating scale of the intraoperative assessment tool.