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Year : 2017  |  Volume : 33  |  Issue : 1  |  Page : 41-47

Stepwise case selection using Guy's stone score reduces complications during percutaneous nephrolithotomy training

1 Department of Urology, Sri Sathya Sai Institute of Higher Medical Sciences, Prasanthigram, Andhra Pradesh, India
2 Department of Urology, Institute of Nephrology and Urology, Medanta – The Medicity, Gurgaon, Haryana, India

Date of Submission17-Jun-2016
Date of Acceptance10-Aug-2016
Date of Web Publication2-Jan-2017

Correspondence Address:
Jiten Jaipuria
Department of Urology, Sri Sathya Sai Institute of Higher Medical Sciences, Prasanthigram, Andhra Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0970-1591.195757

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Introduction: Traditional percutaneous nephrolithotomy (PCNL) training involved subjective award of cases to the trainee. We restructured this according to the Guy's stone score (GSS) such that each trainee stepwise completed 25 cases of each grade before progressing. This study compares the outcomes of training with traditional versus stepwise approach.
Methods: Four hundred consecutive cases equally distributed for two trainees in each group were compared in terms of complications (Clavien-Dindo), stone free rate (SFR), operative and fluoroscopy time. External comparison was also done against a benchmark surgeon. Multivariable regression model was created to compare SFR and complications while adjusting for comorbidity, Amplatz size, access tract location, number of punctures, body mass index, stone complexity, and training approach.
Results: The distribution of cases in terms of calculus complexity was similar. Overall, in comparison to traditional training, stepwise training had significantly shorter median operative time (100 vs. 120 min, P < 0.05), fluoroscopy time (136 vs. 150 min, P < 0.05) and fewer overall (29.5% vs. 43.5%, P < 0.005) as well as major complications (3% vs. 8.5%, P - 0.029), though initial SFR was higher but not statistically significant (77% vs. 71.5%). On multivariable analyses, stepwise training was independently associated with lower complications (odds ratio 0.46 [0.20–0.74], P - 0.0013) along with GSS grade, number of punctures, and Amplatz size. Stepwise training had similar fluoroscopy time, major complications and final clearance rate compared to expert surgeon.
Conclusions: PCNL has a learning curve specific for each grade of calculus complexity and stepwise training protocol improves outcomes.

How to cite this article:
Jaipuria J, Suryavanshi M, Desai AP, Goyal S, Patel K, Parhad SS, Subudhi SK, Rao CV, Kumar SP, Sen TK. Stepwise case selection using Guy's stone score reduces complications during percutaneous nephrolithotomy training. Indian J Urol 2017;33:41-7

How to cite this URL:
Jaipuria J, Suryavanshi M, Desai AP, Goyal S, Patel K, Parhad SS, Subudhi SK, Rao CV, Kumar SP, Sen TK. Stepwise case selection using Guy's stone score reduces complications during percutaneous nephrolithotomy training. Indian J Urol [serial online] 2017 [cited 2023 Mar 23];33:41-7. Available from:

   Introduction Top

The incidence of renal stones is increasing, and percutaneous nephrolithotomy (PCNL) is considered the gold standard treatment for large and/or complex renal stones.[1],[2] However, it is regarded as the “most complicated stone surgery technique to teach.”[3] Acquiring proficiency in surgical skills during residency should be a priority, as evidence suggests that surgeons who performed more PCNLs during residency continued to be more comfortable while performing the procedure outside residency.[4]

Stone free rate (SFR) and complications are important clinical end points for PCNL and have been used as surrogate markers for assessing competence and learning curve.[5] Overall SFR after PCNL have been reported as 76% by The Clinical Research Office of the Endourological Society.[6] However, comparing SFR between studies is difficult because calculus complexity was not uniformly graded, and definition of SFR and its method of assessment was not standardized.[7]

PCNL training in such a situation offers additional unique challenges as trainees may have inherent variability in skill levels and training exposure can vary.[8] Moreover, institutional practice patterns can vary in terms of instrumentation and preferring interventional radiologists to obtain access, and not all may have a preprocedure training module to teach procedural techniques in a lab environment. Finally, there is no set benchmark (in terms of outcomes) standardized by stone complexity even for training institutes. Guy's stone score (GSS) was described in 2011 to objectively grade calculus complexity and is summarized in [Table 1].[9] It has been externally validated and also found to be associated with complications.[10],[11]
Table 1: Guy's stone scoring system

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Traditional PCNL training was based on an apprenticeship model where trainee was awarded cases with subjective assessment of calculus complexity.[3],[5] We hypothesized that a stepwise structured training program where trainee performed a particular number of cases of each calculus grade (based on objective assessment of calculus complexity) prior to progressing, could perform better.

   Methods Top

Ours is a high volume tertiary care center-based in rural India providing free of cost health services. It has an established PCNL training program since 1992, and admits two trainees per year while performing more than 450 PCNLs/year under a constant academic team with trainers having individual teaching experience of 7–27 years.

Traditional training method involved the use of a validated vegetable model for puncture followed by supervised per cutaneous nephrostomies under fluoroscopic guidance in cases with obstructed nephropathy and dilated pelvicalyceal systems.[12] This was followed by learning PCNL via an apprenticeship method where the first 30 cases were explicitly supervised with a trainer scrubbed along with the trainee, and help available for remainder cases. Cases were awarded with tendency to give simpler cases in beginning based on the subjective decision of trainer. In the step-wise training model, each trainee would complete 25 cases of particular GSS grade before moving higher. Initial 25 GSS Grade 1 cases would remain explicitly supervised with trainer scrubbed along with the trainee, with help available for remainder cases. For external validation and benchmarking, our institute collaborated with a tertiary care urban hospital in Northern India which maintained a similarly structured prospective PCNL database.

With Institutional Review Board clearance, this study compared outcomes in terms of complications (modified Clavien-Dindo classification for PCNL), SFR (defined as residual calculi <4 mm), operative time (defined as from when patient was anesthetized, and till when patient was extubated), and fluoroscopic time between first 100 consecutive PCNLs performed by each of two trainees in 2015 (trained by stepwise protocol) and two new junior consultants in 2014 (trained by traditional protocol with self-reported prior independent PCNL exposure of less than 10 cases).[13]

Outcome data for stepwise training group is also compared against benchmark PCNL database of reference hospital. Benchmarking of trainers/experts across ours and reference hospital has been done by us in a separate study and not further discussed here.[14] Additional multivariable analyses of SFR and complications was done while adjusting for Charlson Comorbidity Index Score, body mass index, the Amplatz size, access tract location (whether infracostal or supracostal), the number of punctures, calculus complexity defined by GSS, and type of training (stepwise vs. traditional).

Briefly, patients at our institute undergo prone fluoroscopic guided PCNL with renal access obtained by urologist via triangulation technique planned on preoperative computed tomography (CT) scan.[15] Complete staghorn calculi are staged by protocol to two or rarely three sessions. At the end of 1 month, patients are assessed for any residual calculi by means of X-ray (in case of radiodense calculi) and/or USG (in case of radiolucent calculi). We prefer pulsed over continuous fluoroscopy.

PCNLs in the benchmark hospital are performed by expert surgeons with individual experience of >1000 cases. Broadly, their patient management protocol, PCNL technique, and C-arm machine (with settings) are similar. However, while we use rigid nephroscope and pneumatic LithoClast, they have ultrasonic as well as pneumatic LithoClast, along with the availability of lasers and flexible nephroscope.

Statistical analyses and sample size estimation

Data are described as median (interquartile range) and numbers (proportion). Analyses of variance (either one-way analysis of variance [ANOVA] or Kruskal–Wallis test [depending on distribution of residuals], with Student–Newman–Keuls or Conover pairwise comparison of subgroups, respectively) was used for simultaneous comparison of multiple groups. Chi-square test was used to compare the categorical variables. For multivariable analyses, stepwise logistic regression models (entered if P < 0.05 and removed if P > 0.1) were created and odds ratio (OR) reported with 95% confidence interval. GSS was analyzed as categorical variable with four categories. All hypothesis testing was done using MedCalc v 15.8 (MedCalc Software, Ostend, Belgium) assuming two-tailed alpha <0.05 as statistically significant (including pairwise comparison of subgroups while doing ANOVA).

   Results Top

Patient management protocols and training team with teaching methods remained constant throughout the study period. Both trainees in 2015 (stepwise training group) completed first 100 PCNLs from January 2015 to October 2015, whereas both junior consultants (traditional training group) completed 100 PCNLs from March 2014 to December 2014. [Table 2] summarizes the demographic and perioperative details of patients in stepwise and traditional training groups with comparative data for benchmark surgeon. All three groups were similar in patient characteristics, calculus complexity, and access tract distribution. Stepwise training group had significantly shorter fluoroscopy (median 136 vs. 150 seconds, P < 0.05) and overall median operative time (median 100 vs. 120 minutes, P < 0.05) in comparison to traditionally trained group.
Table 2: Demographic and perioperative details of patients in stepwise and traditional training groups with comparative data for benchmark surgeon

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[Table 3] summarizes the outcome characteristics of all three groups of surgeons. In comparison to traditionally trained surgeons, stepwise training group had significantly fewer overall (29.5% vs. 43.5%, P < 0.005), as well as major complications (defined as Clavien ≥3a, 3% vs. 8.5%, P - 0.029). No patient in the stepwise training group encountered a ≥3b Clavien-Dindo grade complication event, while there were eleven such cases in the traditionally trained group. Overall, in comparison to traditional training, immediate SFR was higher in stepwise training (77% vs. 71.5%) though statistical significance was not achieved (P - 0.25), however, significantly more patients achieved stone free status across GSS grade 4. Lastly, after auxiliary procedures, at the end of 1 month, SFR was similar in both groups (89.5% vs. 85%). On comparing both groups in multivariable analysis - GSS grade, Amplatz size (OR 1.20 [1.09–1.31], P - 0.0001), number of punctures (OR 1.94 [1.20–3.15], P - 0.0071), and stepwise training (OR 0.46 [0.20–0.74], P - 0.0013) emerged independently associated with complications.
Table 3: Outcome details of patients in stepwise and traditional training groups with comparative data for benchmark surgeon

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Further, in comparison to benchmark surgeon [Table 2], though operative time was higher in the stepwise training group (100 vs. 90 minutes, P - 0.05), fluoroscopy time was not statistically different (136 vs. 120 seconds). Also, though expert surgeon had significantly fewer overall complications in comparison to the stepwise training group ([Table 3], 14% vs. 29.5%, P - 0.018), major complication rate was similar (3% in both groups). Lastly, though immediate SFR was higher for expert surgeon in comparison to stepwise training group (89% vs. 77%, P - 0.038), final SFR after all auxiliary procedures was similar (92.8% vs. 89.5%).

   Discussion Top

Previous literature uses various methods to evaluate PCNL learning curve including complication rate, SFR, operative time, and fluoroscopy time.[5],[16],[17],[18] A common theme observed was that surgical competence could be achieved at around sixty patients, whereas excellence is achieved after slightly more than 100 cases. Use of ultrasound guidance suggested no different results.[19] However, all previous studies relied on subjective assessment of calculus complexity with no explicit mention of attempt to stratify stone complexity, or introduce trainee in a graded manner to more complex stones, and reporting of complications has only recently been standardized.[13] Our study is the first to evaluate the incorporation of an objective calculus complexity score in tailoring PCNL training, and recently many more such scores have been described.[20],[21],[22] We could find only one study which reported the results of PCNLs performed by trainees where calculi were graded by an objective score and authors reported no impact of STONE score on fluoroscopy time.[23]

Experience of the surgeon is a recognized factor influencing outcomes and our study demonstrates that PCNL has learning curve “specific for each grade of calculus complexity,” and blanket figures (ranging from 30 to 100) reported in literature may be an oversimplification.[5],[16],[17],[18],[22] Moreover, in our study, most major complication events happened when higher grades of calculus complexity were tackled early in the learning curve (especially during first fifty cases) even though expert help was always available. Furthermore, we found that for both traditional and stepwise training groups the skill of the surgeon continued to grow, and complete clearance with no major complications was achieved in all cases of GSS 1 and 2 grade calculi which were operated beyond thirty and sixty case mark respectively. Also, improved results were seen for GSS 3 grade calculi operated beyond eighty case mark. A philosophy similar to ours has been explored by Kallidonis et al. where they have divided PCNL training into five modules which starts with initial animal laboratory course and progresses to step wise acquisition of PCNL skills culminating to single stone and large stone management in clinical cases.[16] They reported the results where trainees achieved operative and fluoroscopy time and complications similar to mentor after thirty cases.

Trainers also reported relaxed influence subjectively (in comparison to previous years) while helping stepwise training program trainees learn finer skills of the surgery, as the initial thirty explicitly proctored cases were simple ones. Paradoxically, we realized that stepwise trained trainees subjectively needed less support from attending consultants while dealing with more difficult calculi (whether in terms of failing to achieve a puncture, or achieve complete stone clearance, or encounter a complication event) than traditionally trained trainees, and yet achieved better outcomes. We believe this happened because trainees were better positioned in the learning curve when their turn came to deal with more complex calculi. This led us to acknowledge that cognitive skills of trainees develop not just by guiding influence of trainers, but there is also a significant element of “self-learning” while climbing the learning curve. Self-learning got further boost with higher confidence as trainees tackled simpler calculi with very few complications which could otherwise lower their morale, and by the time first GSS 3 case was encountered; trainees had already acquired reasonable experience and skill to avoid major complications on their own while simultaneously achieving good calculus clearance. Trainers also sobered to the fact that their mere presence is no guarantee against complications, and in a training situation, sometimes trainer just cannot be superior to the trainee regarding ultimate outcome experienced by the patient.

Our trainees provided a positive feedback during pilot as well as continuation phase of protocol where they felt objective assessment of complexity while award of cases made training program impartial, which enhanced their faith and reduced negative competitive attitude, and also reduced the fear of unknown subjective bias in training methods of trainers by potential influence of factors such as liking for a particular candidate or partisan assessment of his/her surgical competence. Trainers also reported higher trust in giving autonomy while award of more complex cases to restructured program trainees due to proven track record with simpler cases.

There is however limitation related to the external validity of our study. There may not be many centers in the world performing 450 PCNLs/year and they may find it difficult to follow our strict protocol where a trainee waits his turn before being awarded a higher GSS grade case, and yet completes his training in reasonable time. Moreover, though data were collected in a prospectively maintained registry with clear intent for audit and a working hypothesis; both groups were not trained concurrently. Further, there is a possibility of inherent difference in surgical skill of surgeons in the two study groups (though there is no reason to believe so) which could bias results. However, previously, complication events for 3 consecutive years since 2012 for novice surgeons were noted to be relatively constant, signifying a fundamental change independent of training methods or skill of trainee. Finally, our institute admits two trainees per year and thus we powered our study as a proof of concept for a cohort of four trainees. Thus, further validation of our protocol in different institutes is necessary before general recommendations can be made.

Yet, our study has important lessons, and becoming conscious about the objective assessment of calculi during award of cases to trainee, with the possibility of grade wise audit of outcomes against own as well as external benchmark (with potential to tailor training program to individual trainee's skill level based on the assessment of calculus complexity grade wise progress of acquisition of surgical skills), may itself increase supervision, improve outcomes, and reduce complications, as similar behavior is seen when surgeons become aware of their fluoroscopy time.[24] Moreover, our approach can be used by institutions to award and audit surgical privileges to individual members of a surgical team comprising members with varying levels of experience. Finally, introduction of objective calculus complexity scores has now made it possible for training institutes to define as to what level of training (beyond just numbers) is imparted to trainees, thus allowing qualitative comparative evaluation of training programs.

Based on our study and other literature, we suggest elements of an audit-based PCNL training program in [Figure 1].[5],[7],[9],[12],[16],[19],[20],[21],[25],[26],[27],[28]
Figure 1: Elements of an audit based percutaneous nephrolithotomy training program

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   Conclusions Top

Introduction of objective scoring systems for stone complexity has allowed the possibility of improved audit in PCNL training. PCNL has a cumulative learning curve specific for each grade of calculus complexity and structuring training such that a trainee exhibits competence with a lower grade of calculus complexity, prior to moving to a higher grade leads to improved outcomes, with fewer complications, when compared to the traditional structure of training.


We wish to acknowledge Dr. Venkatesh Krishnamoorthy and Dr. Maneesh Sinha for their support and guidance to the percutaneous nephrolithotomy training and academic program in Sri Sathya Sai Institute of Higher Medical Sciences.

Financial support and sponsorship:


Conflicts of interest:

There are no conflicts of interest.

   References Top

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  [Table 1], [Table 2], [Table 3]


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