Primary SWL Is an Efficient and Cost-Effective Treatment for Lower Pole Renal Stones Between 10 and 20 mm in Size: A Large Single Center Study

Abstract

Introduction:

To assess the clinical features, outcomes, complications, and cost-effectiveness of shockwave lithotripsy (SWL), flexible ureterorenoscopy (FURS), and percutaneous nephrolithotomy (PCNL) in the treatment of lower pole (LP) stones (10–20 mm) in a large tertiary referral center.

Patients and Methods:

Consecutive patients treated for solitary LP stones (10–20 mm) between 2008 and 2013 were identified from a prospective database. SWL was used as primary treatment in all cases (following a stone multidisciplinary team assessment), with FURS and PCNL reserved for SWL contraindications, failure, or patient choice. “Success” was defined as stone free and/or clinically insignificant stone fragments (≤3 mm) at 1 and 3 months follow-up. Effect of anatomy on SWL success was determined from using CT images and regression analysis. Average cost per treatment modality (including additional second-line treatments) was calculated for each group using the National Health Service England 2014/15 National Tariff Healthcare Resource Group codes.

Results:

Two hundred twenty-five patients were included (mean age 54.9; median stone size 12 mm). One hundred ninety-eight (88%), 21 (9.3%), and 6 (2.7%) patients underwent SWL, FURS, and PCNL as primary treatments, respectively, for median stone sizes of 12, 12, and 20 mm. Overall success rates were 82.8%, 76.1%, and 66.7%, respectively (p < 0.05). Sixty-three percent of patients undergoing primary SWL were effectively treated after one session. Anatomical analysis determined infundibulopelvic angle and infundibular length to be significantly different in patients effectively treated with SWL (p = 0.04). The average cost per treatment modality was also significantly lower for SWL (£750) than for FURS (£1261) or PCNL (£2658) (p < 0.01).

Conclusion:

SWL is both an efficacious and cost-effective primary treatment for patients with solitary LP stones (10–20 mm). The majority of patients can be effectively treated with primary SWL in a dedicated stone center, with the benefits of a short length of stay, low complication, and auxiliary treatment rates. The referral of such patients to high-volume lithotripsy centers with demonstrable outcomes should be given due consideration.

Introduction

There remains clinical uncertainty over which treatment to routinely select for treating lower pole (LP) stones between 1 and 2 cm, as the optimal treatment is yet to be determined.¹ LP stones are more difficult to treat because of the presence of anatomical factors that make clearance of stones more difficult.^2,3

The European Association of Urology guidelines⁴ state that shockwave lithotripsy (SWL) is efficacious and that treatment success is dependent on size, location, and composition of the stone, as well as patient factors. It provides definitive guidance for the first-line treatment of small (<10 mm) LP stones with either SWL or flexible ureterorenoscopy (FURS) and large (>20 mm) LP stones with percutaneous nephrolithotomy (PCNL). However, the choice for primary management of medium-sized (10–20 mm) LP stones remains contentious. SWL is currently recommended preferentially over FURS and PCNL in the absence of “unfavorable” stone composition and anatomical factors.⁴

Global healthcare expenditure and inflation are rising rapidly as new technologies enter the market; therefore cost-effectiveness studies are vitally important to help justify these interventions. Although some studies have assessed the efficacy⁵ and cost-effectiveness⁶ of SWL for treating smaller (mean <10 mm) LP stones, the clinical and fiscal performance of SWL for treating larger (10–20 mm) LP stones is yet to be determined.

The aim of the study was to assess the outcomes, complications, and overall cost-effectiveness of the treatment of consecutive LP stones, between 10 and 20 mm, in a large tertiary referral center, which routinely uses primary SWL for LP stones of this size.

Patients and Methods

We conducted a review of our prospectively maintained SWL database and endourologic operation notes spanning a 5-year continuous period (January 2008–2013). All consecutive stone patients undergoing primary treatment for solitary LP stones between 10 and 20 mm were identified. Patients below the age of 18 or with multiple stones were excluded.

All patients referred with urolithiasis have their radiologic imaging reviewed at a weekly Stone multidisciplinary team meeting. We use a “trimodal” protocol for the treatment of solitary LP stones between 10 and 20 mm. Patients were typically triaged to SWL treatment, unless excluded through contraindication (ongoing anticoagulant therapy, pregnancy, and a skin-to-stone distance [SSD] >14 cm), or patient choice. FURS and PCNL were typically used as second- or third-line treatments (SWL failures) or as primary treatments in a small group of patients (the SWL exclusions).

SWL was undertaken in the outpatient setting using a Sonolith lithotripter (Technomed Medical Systems, Vaulx-en-Velin, France), with sedoanalgesia (100 mg rectal diclofenac ± as much as 1 mg intravenous Alfentanyl). The medial parts of the LP stones are targeted initially in order that fragments are able to pass through the infundibulum into the renal pelvis.

FURS was performed using Olympus flexible ureteroscopes, 200 or 365 micron laser fibers, and a VersaPulse PowerSuite 20 W Holmium:YAG laser (Lumenis, Inc., California).⁷

PCNL was performed under general anesthesia in the prone position, using Alken dilators (Karl Storz, Tuttlingen, Germany), a 27F nephroscope (Wolf, Illinois), and an ultrasonic lithotripter (Karl Storz, Tuttlingen, Germany; LithoClast Master, EMS, Nyon, Switzerland).⁸ Mean screening times, mean exposure and mean operative times for SWL, FURS and PCNL are shown in Appendix Table 1.

“Success” was defined as stone free (SF) and or clinically insignificant stone fragments (CISF) (≤3 mm) at 1 and 3 months follow-up using either plain X-ray KUB (radiopaque), renal ultrasound (radiolucent), or CT-KUB, as has been reported in many previous studies.^9
–11 As much as three separate sessions of SWL and as much as two sessions for FURS were given before definitive determination of outcome. Complications were graded using the Clavien-Dindo system.¹² For patients in the SWL group, the infundibulopelvic angle (IPA), infundibular width (IW), and infundibular length (IL) were analyzed from CT imaging,^13,14 and SSD at 0°, 45°, and 90° was recorded, and the average of the three was calculated¹⁵ (Fig. 1).

FIG. 1.

Measurement of the infundibulopelvic angle (A), infundibular width (B), infundibular length (C), and skin-to-stone distances at 0°, 45°, and 90° (D).

The cost analysis was performed by calculating the cost per procedure using price tariffs from National Health Service England 2014/2015 National Tariff Healthcare Resource Group codes,¹⁶ illustrated in Table 4, with one session of outpatient SWL costing £459, FURS costing £907–£1173, and PCNL costing £2352–£2811. The cost of an additional ureteral stent insertion was £1058.

Statistical analysis was performed using SPSS version 21 (Chicago, IL). Categorical variables were compared using the chi-squared test, and continuous variables were analyzed using the one-way ANOVA with post hoc Tukey test. Statistical significance was set at p < 0.05. Univariate regression analysis was performed of all anatomical factors that were predictors of SWL failure; those significant on univariate analysis were assessed by multivariate regression analysis to assess if they were independent predictors of SWL failure.

Results

A total of 225 patients with solitary LP calculi between 10 and 20 mm were included in the present study. One hundred ninety-eight patients (88%) underwent primary SWL, while 21 (∼9%) underwent primary FURS and 6 (∼3%) underwent primary PCNL. The demographics and stone features are shown in Table 1.

Table 1.

Demographic and Stone Characteristics of the Shockwave Lithotripsy, Percutaneous Nephrolithotomy, and Flexible Ureterorenoscopy Groups

Parameters	SWL (n = 198)	FURS (n = 21)	PCNL (n = 6)	p
Mean (SD) age (years)	54.1 (13.3)	62.2 (15)	55.2 (20.3)	0.05
Median age (years)	54	62	62
Male: female (%)	73: 27	52: 48	50: 50	0.001
Mean (SD) stone size (mm)	12.4 (2.4)	13.1 (3.7)	16.8 (4.9)	0.09
Median stone size (mm)	12	12	20
Left: right (%)	57: 43	62: 38	50: 50	0.06

SD = standard deviation; SWL = shockwave lithotripsy; PCNL = percutaneous nephrolithotomy; FURS = flexible ureterorenoscopy.

The detailed analysis of treatment outcomes, complications, and length of stay (LOS) are illustrated in Table 2. The cumulative success rates of primary SWL following the first, second, and third treatments were 62.6%, 79.8%, and 82.8%, respectively. There was no significant difference in overall success rate between the three groups. There was a statistically significant lower complication rate and lower mean LOS in the SWL group in comparison to the FURS and PCNL groups (p < 0.05). The mean number of shocks was 3720, and mean power was 71 kV for the SWL group.

Table 2.

Clinical Outcomes of the Different Primary Treatments for Lower Pole Stones, Illustrating Success Rates, Stone-Free Rates, Complications, and Length of Hospital Stay

Primary treatment	SWL (n = 198)		FURS (n = 21)	PCNL (n = 6)	p
Success, n (%)	164 (82.8)		16 (76.2)	4 (66.7)	0.47
Stone free	96 (48.5)		9 (42.9)	4 (66.7)	0.59
CISF (≤3 mm)	68 (34.3)		7 (33.3)	0 (0)
Success, n (%) after a single treatment session	124 (62.6)		14 (66.7)	4 (66.7)	0.92
Stone free	77 (38.9)		8 (38.1)	4 (66.7)	0.39
CISF (≤3 mm)	47 (23.7)		6 (28.6)	0 (0)
Mean No. of treatments (SD)	1.4 (0.7)		1.1 (0.3)	1 (0)	<0.03
1 treatment	134 (68.7)		19 (90.5)	6 (100)
2 treatments	51 (25.8)		2 (9.5)	—
3 treatments	10 (5.1)		—	—
4 treatments	3 (1.5)		—	—
Complications, n (%)	6 (3.0)		2 (9.5)	2 (33.3)	0.006
Grade I	4 (2.0)		—	1 (16.7)
Grade II	1 (0.5)		1 (4.8)	1 (16.7)
Grade III	1 (0.5)		—	—
Grade IV	—		1 (4.8)	—
Mean (SD) LOS, days	0 (0.4)		2.4 (3.5)	6.6 (3.8)	<0.001
Median LOS (d)	0		1	5
Second-line (auxiliary) treatment	FURS (n = 10)	PCNL (n = 3)	PCNL (n = 2)	SWL (n = 1)
Success, n (%)	7 (70.0)	3 (100.0)	2 (100.0)	1 (100.0)
Stone free	3 (40.0)	2 (66.7)	1 (50.0)	0 (0)
CISF (≤3 mm)	4 (30.0)	1 (33.3)	1 (50.0)	1 (100.0)
No. of treatments
1	9 (90.0)	3 (100.0)	2 (100.0)	—
2	1 (10.0)	—	—	1 (100)
Complications, n (%)	1 (10.0)	0 (0)	1 (50.0)	0 (0)
Grade I	—	—	—	—
Grade II	1 (10.0)	—	1 (50.0)	—
Grade III	—	—	—	—
Grade IV	—	—	—	—
Mean (SD) LOS, (days)	0.8 (0.6)	1.7 (1.2)	10 (4.2)	0 (0)
Median LOS, (days)	1	1	10	0
Overall success	173 (87.4)		18 (85.7)	5 (83.3)	0.94

CISF = clinically insignificant stone fragments; LOS = length of stay.

The overall complication rate of 278 SWL treatments (both as primary and secondary treatment) was 2.2% and is summarized in Table 3. All were grade I, except for a case of urinary tract infection requiring antibiotics (grade II) and an obstructed ureter requiring stenting (grade IIIb). Thirty-four FURS treatments were performed in total with an overall complication rate of 8.8%. All were grade II or less, except for one patient requiring intensive care unit admission (grade IV). The complication rate of the 11 PCNL treatments was 27.2%, all grade II or less.

Table 3.

Complications by Modality, Including Both Primary and Secondary Treatments

Modality	SWL	FURS	PCNL
Number of treatment sessions, (primary only)	278	34	11
Complication, n (%)	6 (2.2)	3 (8.8)	3 (27.2)

Cost-Effectiveness

Table 4 shows a summary of the cost analysis for the study. The mean cost for stone treatment was £750 for SWL, £1261 for FURS, and £2658 for PCNL, and this was significantly different (p < 0.001). We also performed a “worst case” scenario for cost-effectiveness, whereby all 12 primary SWL patients lost to follow-up were assumed to have undergone subsequent FURS, which increased SWL cost by £55, but this was still significantly lower than other modalities (p < 0.001).

Table 4.

Cost Analysis Breakdown for the Shockwave Lithotripsy, Flexible Ureterorenoscopy, and Percutaneous Nephrolithotomy Groups

Primary treatment	SWL (n = 198)			FURS (n = 21)	PCNL (n = 6)	p
No. of treatments	278			23	6
Total cost (£)	128,660			21,330	15,030
Second-line treatment/additional procedures (auxiliary treatment)	FURS (n = 13)	PCNL (n = 3)	Stent insertion (n = 1)	PCNL (n = 2)	SWL (n = 1)
No. of treatments	14	3	1	2	2
Total cost (£)	12,925	7056	1058	5163	918
Total
Overall cost	148,641			26,493.00	15,948.00
Mean cost per patient (£)	750.71			1261.57	2658.00	SWL vs FURS: ≤0.001
						SWL vs PCNL: ≤0.0001
						FURS vs PCNL: ≤0.0001

Analysis of anatomical factors

Table 5 shows the comparison of anatomical factors for effective and stone-free outcomes in the SWL treatment group. Both mean IPA and mean IW were significantly larger in patients effectively treated with SWL (in comparison to those unsuccessfully treated) (p = 0.04). None of the anatomical variables were found to reach statistical significance as independent predictors for specifically stone-free status (for IPA, p = 0.08 and 0.07 on univariate and multivariate analysis, respectively).

Table 5.

Comparison of Anatomical Factors for Effective and Stone-Free Outcomes After SWL: Infundibulopelvic Angle, Infundibular Length, Infundibular Width, and Skin-to-Stone Distance

	Effective outcome			Stone-free outcome
Anatomical factor	Yes (n = 119)	No (n = 27)	p	Yes (n = 72)	No (n = 74)	p
Mean (SD) IPA (°)	57.1 (15.2)	54.0 (15.6)	0.04	57.4 (15.4)	55.7 (15.2)	0.07
Mean (SD) IL (mm)	20.8 (4.8)	22.5 (4.1)	0.66	21.4 (4.4)	20.8 (4.9)	0.31
Mean (SD) IW (mm)	6.6 (2.8)	5.9 (1.8)	0.04	6.3 (2.5)	6.6 (2.9)	0.31
Mean (SD) SSD (mm)	102.8 (24.2)	105.3 (17.9)	0.91	104.3 (22.3)	102.2 (24)	0.99

Data for anatomical factors were available for 146 (73.7%) patients undergoing primary SWL. Mean IPA and mean IW were statistically significantly different for an effective outcome following SWL.

IPA = infundibulopelvic angle; IL = infundibular length; IW = infundibular width; SSD = skin-to-stone distance.

Discussion

The debate regarding the optimal treatment of LP renal stones has endured over time, partly due to improvements in outcomes with flexible ureteroscopy and partly because of the wide variation in SWL outcomes.^4,17 It is evident from United Kingdom urologic lithotripsy practice that an enormous variation exists regarding volume of practice, availability, and continuity of treatment (mobile vs fixed site lithotripters) and the experience and expertise of personnel delivering this treatment.¹⁷ These factors clearly conspire to effect wide variance in treatment outcomes, which can be disappointing.^4,17

–20 Consequently, there exists both controversy and reluctance to the use of lithotripsy within the urologic community.¹⁷

The results of this large study, conducted in a high volume center, demonstrate the efficacy and cost-effectiveness of using SWL as a routine primary treatment of LP stones between 10 and 20 mm. Lithotripsy demonstrated comparable success rates to FURS and PCNL. Furthermore, SWL had a significantly lower complication rate and was significantly more cost-effective than FURS and PCNL (p < 0.001).

There are several strengths to this study: first, this is the largest study evaluating predictive anatomical factors for SWL efficacy in treating LP stones (10–20 mm); and second, this is the only study to evaluate the cost-effectiveness of SWL for treating LP stones of this size. A previous comparatively large study of 221 SWL patients was reported by Ozturk and colleagues,²¹ but without any analysis of anatomical predictive factors for SWL success, nor any cost-effectiveness analysis. Koo and colleagues⁶ previously assessed cost-effectiveness of SWL for the treatment of smaller LP stones (mean 8.5 mm).

The overall validity of this cost-effectiveness study was aided by there being no significant difference in mean stone sizes between the groups (p = 0.09). Treatment outcomes were determined from a prospectively maintained database from consecutive patients and should therefore represent realistic SWL outcomes. Finally, a standard criterion was used for the definition of treatment success (SF/CISF ≤3 mm).^5,6,19,21,22

We acknowledge a number of weaknesses in this study, which include the level of evidence and mismatch of patient numbers across the three study groups. This does not purport to be a randomized controlled trial (RCT) and, hence, is not an unbiased comparison of the three treatment modalities. The numbers of patients in the FURS and PCNL groups are far lower than the SWL group. However, this is an inevitable consequence of our use of SWL as the routine primary treatment modality, due to its proven efficacy in our institute.²³ There was also a significant difference in patient age across the treatment groups, with older patients in the FURS group, with a higher proportion anticoagulant treatment, which may have had an adverse effect on treatment outcomes.

We recognize the emphasis of treatment success being defined by either CISF or true stone-free rate (SFR), which is consistent with previous reports.^5,6,19,21,22 A potential disadvantage of using this term for success is that this does not represent the true, absolute stone-free rate. However, while true SFR remains the ideal goal for all treatment, one has to interpret this term in different studies with a degree of caution, principally due to the variations in interpretation, the heterogeneity in imaging modalities used, and the inherent accuracy of imaging protocols. Some studies have used the SFR term to include fragments <3 mm,^5,21,22 while others^5,6 have relied exclusively on ultrasound for follow-up imaging, which has inherent limitations in sensitivity, as well as user-dependent accuracy.²⁴ The argument for absolute SFR, utilizing CT-KUB follow-up, is diminished when the limited sensitivity of such imaging (due to altered slice thickness and low-dose protocols) is taken into account, as these factors may result in significantly reduced sensitivity (60%) for detecting renal stones <3 mm.²⁵

There have been numerous studies looking at outcomes for the treatment of LP stones between 10 and 20 mm, which have been summarized in recent systematic reviews and meta-analyses.^26,27 The Lower Pole Study Group reported PCNL as the most effective treatment (93% vs 21% success) for stones between 10 and 20 mm.²⁰ However, there are a number of drawbacks to these studies, including the small patient numbers in multiple (n = 18) contributing centers, limited population in the SWL arms (n = 26 for 10–20 mm LP stones), large numbers of different lithotripters used (n = 8), and older technology (in the context of modern lithotripters). More recently, a retrospective study by El-Nahas¹⁹ showed FURS to be superior to SWL for 10–20 mm LP stones. However, not all treatments in the study were primary, as 22.6% of their SWL and 35% of their FURS patients had received prior stone treatment that may have confounded their results. In contrast, our study only included patients with previously untreated stones. A recent RCT by Kumar and colleagues⁵ showed no significant difference in success rates between SWL (78.4%) and retrograde intrarenal surgery (85.4%) for LP stones between 10 and 20 mm, although the treatment arms in the study were limited (n = 35 for SWL). The 82.8% SWL success rate in our study is similar to this RCT.

Our study demonstrates that SWL can be used to treat the majority (88%) of patients referred with solitary LP stones with effective outcomes (∼83%). Moreover, almost two-thirds of patients (63%) undergoing primary lithotripsy were effectively treated after just one SWL session. This observation is noteworthy and merits further comment, as it illustrates that over half (55%) of all patients referred with LP stones can be effectively treated with a single session of SWL. The outcomes of SWL treatment were also achieved with a very low (7%) auxiliary treatment rate, which is lower than the 20% auxiliary procedure rate reported in other studies.²²

The impact of LP anatomy on the success of SWL has been previously reported in multiple studies with mixed results.^13,28 Our study determined mean IPA and mean IW to be statistically significantly different in determining an effective or unsuccessful outcome following SWL (p = 0.04). Logistic regression analysis, however, failed to identify any independent predictors of SF status following SWL (IPA univariate: p = 0.08). These findings are concordant with those of Gupta and colleagues²⁹ in a group of 88 patients. In contrast, a recent prospective study by Torricelli and colleagues¹⁴ reported only the IL to have significant impact on stone-free status, while Madbouly and colleagues²⁸ had found no significance with any of the anatomical factors. Given the wide variation in the literature in addition to the lack of a validated predictive model of SWL success, the emphasis on “unfavorable”⁴ anatomical factors of SWL in 10–20 mm LP stones should perhaps be reevaluated. It is perhaps unsurprising that no clear consensus on the significant anatomical factors which influence SWL outcomes has emerged, as the wide variance in lithotripsy success rates (and proficiency) across different practicing centers is likely to confound the analysis of these factors considerably.

The low SWL complication rate of 4.6% in our study is consistent with the literature.^19,30,31 However, a recent systematic review and meta-analysis showed no significant difference in complication rate between FURS and SWL.³² This contrasts with our study, which demonstrated a significantly higher complication rate for FURS (9.5%) and the PCNL group (33%). However, the 30-day complication rate and median LOS are comparable to those recently published from the United Kingdom PCNL audit.³³

The results of the cost analysis illustrate a significantly lower cost per success of SWL (£750) and demonstrate that SWL is the most cost-effective treatment of solitary LP stones between 10 and 20 mm. Given the financial challenges in global healthcare systems, this study highlights both the clinical and fiscal benefits of SWL as routine primary treatment for such stones. Therefore, we would advocate referral of patients with solitary LP stones between 10 and 20 mm to specialist centers who use SWL as routine primary treatment for suitable patients. We do not suggest that SWL is a replacement for surgery in all cases, but the study does establish the practicality, clinical effectiveness, and cost efficacy of lithotripsy for this group of patients in high volume centers, achieved with low complication rates. This approach may also assist in the service delivery and configuration of endourology resources in large-volume stone institutes.

Conclusion

This study conducted on patients treated in a large specialist tertiary stone referral center demonstrates that using outpatient SWL as a routine primary treatment for stones between 10 and 20 mm is as effective as FURS and PCNL and is more cost-effective than the other modalities. We would advocate using SWL as primary treatment for LP stones (10–20 mm) and reserving the other modalities for the minority of patients (∼12%) who are unsuitable. Consideration should be given to referral of patients to high-volume specialist lithotripter centers to treat more patients cost-effectively.

Footnotes

Acknowledgments

The authors acknowledge the support of their many urologic colleagues in Scotland who continue to refer patients with larger renal pelvic stones to their center for treatment. The authors also acknowledge the contributions of the dedicated team of radiographers in the Scottish Lithotriptor Centre (Anita MacNamara, Carol-Ann Stephenson, Shirley Wallace, Karen Craig, and Ruth Donkin).

Author Disclosure Statement

No competing financial interests exist.

Abbreviations Used

Appendix

Appendix Table 1.

Mean Screening Times, Mean Exposure, and Mean Operative Times for Shockwave Lithotripsy, Flexible Ureterorenoscopy, and Percutaneous Nephrolithotomy

	SWL	FURS	PCNL	p
Mean screening time (minutes)	2.2	0.9	2.7	0.003^a
Mean exposure (cGycm2)	209.3	141	122	0.2^a
Mean operative time (minutes)		95	160	0.002^a

Kruskal–Wallis test.

The screening times were greater with PCNL and SWL than for FURS, but the radiation exposure was not different between the three groups. Pulsed exposure and coning were used for all three types of procedures to minimize exposure.

SWL = shockwave lithotripsy; FURS = flexible ureterorenoscopy; PCNL = percutaneous nephrolithotomy.

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