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Impact of Ureteral Stent Material on Stent-related Symptoms: A Systematic Review of the Literature

  • Matthias Boeykens
    Affiliations
    Department of Urology, Universitair Ziekenhuis Brussel, Vrije Universiteit Brussel, Brussels, Belgium
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  • Etienne X. Keller
    Affiliations
    Department of Urology, University Hospital Zurich, University of Zurich, Zurich, Switzerland

    Young Academic Urologists Urolithiasis and Endourology Working Group, European Association of Urology, Arnhem, The Netherlands

    Progressive Endourological Association for Research and Leading Solutions, Paris, France
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  • Andrea Bosio
    Affiliations
    Department of Urology, Città della Salute e della Scienza, Molinette University Hospital, Turin, Italy
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  • Oliver J. Wiseman
    Affiliations
    Urology Department, Addenbrooke’s Hospital, Cambridge University Hospitals NHS Foundation Trust, Cambridge, UK
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  • Pablo Contreras
    Affiliations
    Servicio de Urología, Hospital Alemán, Buenos Aires, Argentina
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  • Eugenio Ventimiglia
    Affiliations
    Young Academic Urologists Urolithiasis and Endourology Working Group, European Association of Urology, Arnhem, The Netherlands

    Progressive Endourological Association for Research and Leading Solutions, Paris, France

    Division of Experimental Oncology/Unit of Urology, Urological Research Institute, IRCCS Ospedale San Raffaele, Milan, Italy
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  • Michele Talso
    Affiliations
    Young Academic Urologists Urolithiasis and Endourology Working Group, European Association of Urology, Arnhem, The Netherlands

    Department of Urology, ASST Fatebenefratelli-Sacco, Luigi Sacco University Hospital, Milan, Italy
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  • Amelia Pietropaolo
    Affiliations
    Young Academic Urologists Urolithiasis and Endourology Working Group, European Association of Urology, Arnhem, The Netherlands

    Department of Urology, University Hospital Southampton, Southampton, UK
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  • Thomas Tailly
    Affiliations
    Young Academic Urologists Urolithiasis and Endourology Working Group, European Association of Urology, Arnhem, The Netherlands

    Academic Department of Urology, University Hospital Ghent, University of Ghent, Ghent, Belgium
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  • Vincent De Coninck
    Correspondence
    Corresponding author. Department of Urology, AZ Klina, Augustijnslei 100, Brasschaat, Belgium. Tel. +32 3 650 5056.
    Affiliations
    Young Academic Urologists Urolithiasis and Endourology Working Group, European Association of Urology, Arnhem, The Netherlands

    Progressive Endourological Association for Research and Leading Solutions, Paris, France

    Department of Urology, AZ Klina, Brasschaat, Belgium
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Open AccessPublished:October 18, 2022DOI:https://doi.org/10.1016/j.euros.2022.09.005

      Abstract

      Context

      Ureteral stents are essential implants that are used on a daily basis. Since their invention, advances in stent design have been directed towards alleviating stent-related symptoms. It remains unclear how the material composition of the stent affects stent-related symptoms.

      Objective

      To review the literature and define the clinical impact of ureteral stent material on stent-related symptoms.

      Evidence acquisition

      A literature search of the Embase, MEDLINE (PubMed), and Web of Science databases was conducted on December 17, 2021 to collect articles comparing stent composition materials regarding stent-related symptoms. Thirteen publications met the inclusion criteria, of which only one met the high-quality requirements of the Cochrane Collaboration tool for assessing the risk of bias in randomized trials.

      Evidence synthesis

      Most trials, including the highest quality trial, seem to support that silicone double-J (DJ) stents reduce stent-related symptoms compared to nonsilicone DJ stents. Regarding physical properties, it seems that “soft” or “flexible” DJ stents reduce stent-related symptoms. However, since there was only one high-quality study with a low risk of bias, it is impossible to draw a definitive conclusion owing to the lack of quality data.

      Conclusions

      Silicone DJ stents, and by extension “soft” DJ stents, appear to reduce stent-related symptoms compared to nonsilicone polymers and “hard” DJ stents. No definitive conclusion can be drawn owing to a lack of quality evidence. Creating a standard for measuring and reporting physical stent properties should be the first step for further research.

      Patient summary

      A ureteral stent is a small hollow tube placed inside the ureter to help urine drain from the kidney. We reviewed the literature on the impact of stent material on stent-related symptoms. We found that silicone may reduce stent-related symptoms, but no definitive conclusion can be drawn and further studies are needed.

      Keywords

      1. Introduction

      Ureteral stents are essential implants that are used on a daily basis. The downside of these widely used implants is that up to 88% of patients experience at least some form of discomfort [
      • Joshi H.B.
      • Okeke A.
      • Newns N.
      • Keeley Jr, F.X.
      • Timoney A.G.
      Characterization of urinary symptoms in patients with ureteral stents.
      ,
      • De Coninck V.
      • Keller E.X.
      • Somani B.
      • et al.
      Complications of ureteroscopy: a complete overview.
      ,
      • Bosio A.
      • Alessandria E.
      • Dalmasso E.
      • et al.
      How bothersome double-J ureteral stents are after semirigid and flexible ureteroscopy: a prospective single-institution observational study.
      ]. Examination of the stents available on the market reveals a wide variety of stent characteristics, with differences in the overall design, material composition, and coating. Several changes in overall stent design have been introduced in attempts to reduce stent-related symptoms, but the double-J (DJ) stent is still the design most commonly used [
      • Bosio A.
      • Alessandria E.
      • Agosti S.C.
      • et al.
      Loop-tail stents fail in reducing stent-related symptoms: results of a prospective randomised controlled trial.
      ,
      • Dunn M.D.
      • Portis A.J.
      • Kahn S.A.
      • et al.
      Clinical effectiveness of new stent design: randomized single-blind comparison of tail and double-pigtail stents.
      ,
      • Park H.K.
      • Paick S.H.
      • Kim H.G.
      • Lho Y.S.
      • Bae S.
      The impact of ureteral stent type on patient symptoms as determined by the Ureteral Stent Symptom questionnaire: a prospective, randomized, controlled study.
      ,
      • Davenport K.
      • Kumar V.
      • Collins J.
      • Melotti R.
      • Timoney A.G.
      • Keeley Jr., F.X.
      New ureteral stent design does not improve patient quality of life: a randomized, controlled trial.
      ,
      • Bosio A.
      • Alessandria E.
      • Agosti S.
      • et al.
      Pigtail suture stents significantly reduce stent-related symptoms compared to conventional double J stents: a prospective randomized trial.
      ].
      Advances in stent material composition have focused on improving properties such as flexibility, elasticity, biocompatibility, catheter wall thickness (inner/outer diameter [ID/OD] ratio), and surface properties (e.g. porosity, hydrophilicity, and antibacterial properties) affecting encrustation, bacterial adhesion rates, and the friction coefficient [
      • Lennon G.M.
      • Thornhill J.A.
      • Sweeney P.A.
      • Grainger R.
      • McDermott T.E.
      • Butler M.R.
      ‘Firm’ versus ‘soft’ double pigtail ureteric stents: a randomised blind comparative trial.
      ,
      • Liatsikos E.
      • Kallidonis P.
      • Stolzenburg J.U.
      • Karnabatidis D.
      Ureteral stents: past, present and future.
      ,
      • Venkatesan N.
      • Shroff S.
      • Jayachandran K.
      • Doble M.
      Polymers as ureteral stents.
      ]. The first DJ stents introduced to the market were made of silicone, which is considered “soft” and biocompatible [
      • Liatsikos E.
      • Kallidonis P.
      • Stolzenburg J.U.
      • Karnabatidis D.
      Ureteral stents: past, present and future.
      ,
      • Venkatesan N.
      • Shroff S.
      • Jayachandran K.
      • Doble M.
      Polymers as ureteral stents.
      ]. However, at that time, silicone stents showed several limitations. First, the flexibility and lack of hydrophilic guidewires, with silicone causing high interface friction between the stent and the guidewire, resulted in difficult handling [
      • Venkatesan N.
      • Shroff S.
      • Jayachandran K.
      • Doble M.
      Polymers as ureteral stents.
      ,
      • Mardis H.K.
      • Kroeger R.M.
      • Morton J.J.
      • Donovan J.M.
      Comparative evaluation of materials used for internal ureteral stents.
      ,
      • Mosayyebi A.
      • Manes C.
      • Carugo D.
      • Somani B.K.
      Advances in ureteral stent design and materials.
      ]. Second, silicone has high susceptibility to compression, which necessitates an unfavorably low ID/OD ratio and results in lower drainage efficacy [
      • Venkatesan N.
      • Shroff S.
      • Jayachandran K.
      • Doble M.
      Polymers as ureteral stents.
      ,
      • Mardis H.K.
      • Kroeger R.M.
      • Morton J.J.
      • Donovan J.M.
      Comparative evaluation of materials used for internal ureteral stents.
      ,
      • Mosayyebi A.
      • Manes C.
      • Carugo D.
      • Somani B.K.
      Advances in ureteral stent design and materials.
      ]. Consequently, in the search for better material properties, silicone was replaced by polyurethane in the 1980s [
      • Liatsikos E.
      • Kallidonis P.
      • Stolzenburg J.U.
      • Karnabatidis D.
      Ureteral stents: past, present and future.
      ,
      • Venkatesan N.
      • Shroff S.
      • Jayachandran K.
      • Doble M.
      Polymers as ureteral stents.
      ]. Since then, several efforts have been made by manufacturers to further optimize the stent material composition by modifying the polymers used.
      It remains unclear how the chemical and physical properties of stents affect their biocompatibility and tolerability [
      • Lennon G.M.
      • Thornhill J.A.
      • Sweeney P.A.
      • Grainger R.
      • McDermott T.E.
      • Butler M.R.
      ‘Firm’ versus ‘soft’ double pigtail ureteric stents: a randomised blind comparative trial.
      ,
      • Liatsikos E.
      • Kallidonis P.
      • Stolzenburg J.U.
      • Karnabatidis D.
      Ureteral stents: past, present and future.
      ,
      • Joshi H.B.
      • Chitale S.V.
      • Nagarajan M.
      • et al.
      A prospective randomized single-blind comparison of ureteral stents composed of firm and soft polymer.
      ]. Our aim here was to review the literature to identify the clinical impact of ureteral stent material on stent-related symptoms.

      2. Evidence acquisition

      This study was registered in PROSPERO (CRD42022264829). The systematic search was guided by “A systematic approach to searching” [
      • Bramer W.M.
      • de Jonge G.B.
      • Rethlefsen M.L.
      • Mast F.
      • Kleijnen J.
      A systematic approach to searching: an efficient and complete method to develop literature searches.
      ] in accordance with the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) checklist [
      • Page M.J.
      • McKenzie J.E.
      • Bossuyt P.M.
      • et al.
      The PRISMA 2020 statement: an updated guideline for reporting systematic reviews.
      ]. A literature search was conducted by two authors (M.B. and V.D.C) on December 17, 2021, using the Embase, MEDLINE (PubMed), and Web of Science databases.
      We determined a clear and focused question using the PICO (Population, Intervention, Compapartor, Outcome) approach: do adult patients receiving a ureteral stent composed of material A, compared to a ureteral stent composed of material B with the same overall stent design, have more or less stent-related symptoms. Then these PICO elements were used to identify appropriate index terms (Emtree and MeSH) and synonyms in the thesaurus of the databases used. Variations in search terms and database-appropriate syntax with parentheses, field codes, and Boolean operators were used to maximize the yield. Searches were restricted to English-language articles on humans. No restriction on time period was applied.
      All original articles meeting the PICO approach, both retrospective and prospective, and with the outcome measured in any way as an endpoint (not exclusively the primary endpoint) were included. Case reports and meeting abstracts were not considered eligible. Our search strategy, build, and log are provided in the Supplementary material. Figure 1 shows the PRISMA flowchart. The Embase, MEDLINE (PubMed), and Web of Science search yielded 13 articles eligible for inclusion in the review.
      Figure thumbnail gr1
      Fig. 1Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) diagram.
      A formal risk-of-bias analysis was conducted for the studies included using the Cochrane Collaboration risk of bias assessment tool (RoB 2) for the randomized studies (7 of the 13 studies; Table 1, Table 2) and the Cochrane Collaboration risk of bias tool for nonrandomized studies for interventions (ROBINS-I) for the nonrandomized prospective studies (3 of the 13 studies; Table 2, Table 3) and the one nonrandomized retrospective study (Table 2, Table 3) [
      • Higgins J.P.T.
      • Thomas J.
      • Chandler J.
      • et al.
      Cochrane handbook for systematic reviews of interventions.
      ,
      • Sterne J.A.
      • Hernán M.A.
      • Reeves B.C.
      • et al.
      ROBINS-I: a tool for assessing risk of bias in non-randomised studies of interventions.
      ]. Two of the 13 studies were designed as self-controlled case series studies, for which a risk of bias analysis could not be conducted (Table 2). All the formal assessments are detailed in the Supplementary material.
      Table 1Risk of bias assessment for the randomized trials using the Cochrane RoB 2 tool
      StudyBias arising from the randomization processBias due to deviations from intended interventionBias due to missing outcome dataBias in measurement of the outcomeBias in selection of the reported resultOverall
      Lennon (1995)
      • Lennon G.M.
      • Thornhill J.A.
      • Sweeney P.A.
      • Grainger R.
      • McDermott T.E.
      • Butler M.R.
      ‘Firm’ versus ‘soft’ double pigtail ureteric stents: a randomised blind comparative trial.
      Candela (1997)
      • Candela J.V.
      • Bellman G.C.
      Ureteral stents: impact of diameter and composition on patient symptoms.
      Lee (2005)
      • Lee C.
      • Kuskowski M.
      • Premoli J.
      • Skemp N.
      • Monga M.
      Randomized evaluation of ureteral stents using validated symptom questionnaire.
      Joshi (2005)
      • Joshi H.B.
      • Chitale S.V.
      • Nagarajan M.
      • et al.
      A prospective randomized single-blind comparison of ureteral stents composed of firm and soft polymer.
      Mendez-Probst (2012)
      • Mendez-Probst C.E.
      • Goneau L.W.
      • MacDonald K.W.
      • et al.
      The use of triclosan eluting stents effectively reduces ureteral stent symptoms: a prospective randomized trial.
      El-Nahas (2018)
      • El-Nahas A.R.
      • Lachine M.
      • Elsawy E.
      • Mosbah A.
      • El-Kappany H.
      A randomized controlled trial comparing antimicrobial (silver sulfadiazine)-coated ureteral stents with non-coated stents.
      Wiseman (2020)
      • Wiseman O.
      • Ventimiglia E.
      • Doizi S.
      • et al.
      Effects of silicone hydrocoated double loop ureteral stent on symptoms and quality of life in patients undergoing flexible ureteroscopy for kidney stone: a randomized multicenter clinical study.
      The symbol indicates a low risk of bias, indicates an unclear risk of bias, and indicates a high risk of bias.
      Table 2Summary of the studies included and their main characteristics
      Porges S.A.
      StudyStents comparedHydrogel coatingD (Fr)Length (cm)PatientsInclusion criteriaExclusion criteriaSymptom evaluationStent removalUSSQDesignRoBIFConclusion
      Smedley (1988)
      • Smedley F.H.
      • Rimmer J.
      • Taube M.
      • Edwards L.
      168 double J (pigtail) ureteric catheter insertions: a retrospective review.
      Silicone

      Polyurethane
      Unknown

      Unknown
      NANA116All patients needing placement of a DJ stentNADay of stent removalMean D79 (range 1–366)NoRSSeriousNALess loin discomfort and trigonal irritation with a silicone stent (but not significant).
      Pryor (1991)
      • Pryor J.L.
      • Langley M.J.
      • Jenkins A.D.
      Comparison of symptom characteristics of indwelling ureteral catheters.
      Cook polyurethane

      Surgitek Silitek

      Cook C-Flex

      Van-Tec Soft
      Unknown

      Unknown

      No

      Unknown
      722–2473All patients needing placement of a DJ stentBilateral stents, long-term stentD2 and D6 and 7 d after removalD6–D30NoPCSModerateNANo evidence of differences in SRS.
      Lennon (1995)
      • Lennon G.M.
      • Thornhill J.A.
      • Sweeney P.A.
      • Grainger R.
      • McDermott T.E.
      • Butler M.R.
      ‘Firm’ versus ‘soft’ double pigtail ureteric stents: a randomised blind comparative trial.
      Cook polyurethane

      Cook Sof-Flex
      Unknown

      Yes
      622–26155DJ stent placed for ureteral calculi, SWL, and other miscellaneous endourologic interventionsNAAt day of stent removalMean D37 (range 7–182)NoRCTHighNASRS of renal pain, suprapubic pain, and dysuria were significantly higher in the polyurethane (firm) than in the Sof-Flex (soft) group.

      No differences in the presence of reflux pain, urgency, frequency, or hematuria.

      SRS severity was clearly greater with the firm stent.
      Candela (1997)
      • Candela J.V.
      • Bellman G.C.
      Ureteral stents: impact of diameter and composition on patient symptoms.
      Boston
      Microvasive, Boston Scientific.
      Percuflex

      Boston
      Microvasive, Boston Scientific.
      Percuflex Plus
      No

      Yes
      4.8–6NA60Stent for SWL, obstruction, or URSBilateral stents.D7-10D7–D10NoRCTHighNANo evidence of differences in SRS.
      Lee (2005)
      • Lee C.
      • Kuskowski M.
      • Premoli J.
      • Skemp N.
      • Monga M.
      Randomized evaluation of ureteral stents using validated symptom questionnaire.
      Bard Inlay

      Cook Endo-Sof

      Boston
      Microvasive, Boston Scientific.
      Contour

      Applied Medical Vertex

      Surgitek Classic
      Yes

      Yes

      Yes

      Yes

      Yes
      622–3044 (70 included)All patients undergoing unilateral retrograde ureteral stent placementUntreated UTI, bladder cancer, additional transurethral procedures, spinal cord injuryD1, D3, D5 and 30 days after removalNAYesRCTHighNASignificantly fewer urinary symptoms with the Bard Inlay stent than the other stents on D3. The Bard Inlay stent had the most significant positive characteristics, while the Vertex and Surgitek Classic stents were associated with more significant negative characteristics.
      Joshi (2005)
      • Joshi H.B.
      • Chitale S.V.
      • Nagarajan M.
      • et al.
      A prospective randomized single-blind comparison of ureteral stents composed of firm and soft polymer.
      Boston
      Microvasive, Boston Scientific.
      Percuflex Plus

      Boston
      Microvasive, Boston Scientific.
      Contour
      Yes

      Yes
      624130DJ-stent placed after URS and ESWL for stone diseaseNCD, pregnancy, bilateral stents, long-term stent, stenting after PCNLD7, D28, D56D28YesRCTSome concernsNANo evidence of differences in SRS
      El-Nahas (2006)
      • El-Nahas A.R.
      • El-Assmy A.M.
      • Shoma A.M.
      • Eraky I.
      • El-Kenawy M.R.
      • El-Kappany H.A.
      Self-retaining ureteral stents: analysis of factors responsible for patients’ discomfort.
      Coloplast
      Porges S.A.
      silicone

      Boston
      Microvasive, Boston Scientific.
      Percuflex
      Unknown

      Unknown
      6–1424–26100DJ stent placed after endopyelotomy, URS, laparascopic pyeloplasty, or endoureterotomySWL, pregnancy, pre-existing LUTS, complicated procedureDay of stent removalMean D56 (range 28–112)NoPCSSeriousNASignificantly more patient discomfort with the Percuflex (“hard”) stent than with the silicone (“soft”) stent.
      Cadieux (2009)
      • Chow P.M.
      • Chiang I.N.
      • Chen C.Y.
      • et al.
      Malignant ureteral obstruction: functional duration of metallic versus polymeric ureteral stents.
      Boston
      Microvasive, Boston Scientific.
      Percuflex Plus

      Triumph triclosan-eluting stent
      Yes

      No
      NA.NA8Long-term stent for cancer, strictures, or fibrosisNA.Day of stent removalD90NoSCCSNAYesFewer symptomatic UTI's in patients with Triumph® triclosan eluting stents.
      Mendez-Probst (2012)
      • Mendez-Probst C.E.
      • Goneau L.W.
      • MacDonald K.W.
      • et al.
      The use of triclosan eluting stents effectively reduces ureteral stent symptoms: a prospective randomized trial.
      Boston
      Microvasive, Boston Scientific.
      Percuflex Plus

      Triumph triclosan-eluting stent
      Yes

      No
      NA.27 (mean)20Patients requiring short-term stentingNADay of stent removalD 7–D15NoRCTHighYesSignificantly less patient discomfort with Triumph® triclosan eluting stents.
      Chow (2015)
      • Joshi H.B.
      • Newns N.
      • Stainthorpe A.
      • MacDonagh R.P.
      • Keeley Jr, F.X.
      • Timoney A.G.
      Ureteral stent symptom questionnaire: development and validation of a multidimensional quality of life measure.
      Cook Resonance

      Unspecified polymeric stent
      No

      Unknown
      620–3042Cancer patients with malignant ureteral obstructionNo previous polymeric stentNANANoSCCSNANoNo evidence for differences on stent-related symptoms.
      El-Nahas (2018)
      • El-Nahas A.R.
      • Lachine M.
      • Elsawy E.
      • Mosbah A.
      • El-Kappany H.
      A randomized controlled trial comparing antimicrobial (silver sulfadiazine)-coated ureteral stents with non-coated stents.
      Carbothan + hydrogel coating

      Carbothan + silver sulfadiazine
      Yes



      No
      626126DJ stent placement after URS lithotripsy<18 yrDay of stent removalMean 3.1 ± 1.2 wkYesRCTSome concernsNoNo evidence for differences on stent-related symptoms.
      Gadzhiev (2020)
      • Gadzhiev N.
      • Gorelov D.
      • Malkhasyan V.
      • et al.
      Comparison of silicone versus polyurethane ureteral stents: a prospective controlled study.
      Cook Black silicone

      Rüsch
      Teleflex.
      polyurethane
      Unknown

      Unknown
      62650DJ stent placement for acute renal colic due to ureteral stone<18 yr, >60 yr, active UTI, urogenital tumorD1, D14, D28D28NoPCSModerateNo
      The first author (Gadzhiev) is a paid consultant for Cook Medical.
      Silicone stents were associated with lower body pain intensity on VASP at 2 wk before and immediately before stent removal vs polyurethane stents.
      Wiseman (2020)
      • Wiseman O.
      • Ventimiglia E.
      • Doizi S.
      • et al.
      Effects of silicone hydrocoated double loop ureteral stent on symptoms and quality of life in patients undergoing flexible ureteroscopy for kidney stone: a randomized multicenter clinical study.
      Coloplast ImaJin Hydro

      Boston
      Microvasive, Boston Scientific.
      Percuflex Plus
      Yes

      Yes
      626113 (141 included)DJ stent placement after fURS for renal stones (5–25mm)Acute colic pain, UT malformation, urogenital tumor, indwelling DJ stent, untreated UTID2, D7, D20 and D35D20YesRCTLowYesSilicone stents were associated with significantly less patient discomfort and better QoL compared to Percuflex.

      There was a 25% reduction in USSQ pain score (at D20) in favor of silicone.

      Urinary symptoms (relevant USSQ domain) were significantly lower in the silicone group at D2, D7, and D20, with the largest difference evident at D20.
      D = diameter; RS = retrospective study; PCS = prospective cohort study; RCT = randomized controlled trial; SCCS = self-controlled case series; RSCCS = retrospective SCCS; USSQ = Ureteral Stent Symptom Questionnaire; RoB = risk of bias; DJ = double J; IF = industry funding; NA = not available; NOS = Newcastle-Ottawa Quality Assessment Scale; SWL = shockwave lithotripsy; URS = ureteroscopy; UT = urinary tract; UTI = UT infection; LUTS = lower urinary tract symptoms; NCD = noncalculus disease; fURS = flexible URS; PCNL = percutaneous nephrolithotomy; SRS = stent-related symptoms; VASP = Visual Analog Scale for Pain; QoL = quality of life.
      a Porges S.A.
      b Microvasive, Boston Scientific.
      c Teleflex.
      d The first author (Gadzhiev) is a paid consultant for Cook Medical.
      Table 3Risk of bias assessment for the nonrandomized trials using the Cochrane ROBINS-I tool
      StudyBias due to confoundingBias due to selection of participantsBias in classification of interventionsBias due to deviations from intended interventionsBias due to missing dataBias in measurement of outcomesBias in selection of the reported resultOverall
      Smedley (1988)
      • Smedley F.H.
      • Rimmer J.
      • Taube M.
      • Edwards L.
      168 double J (pigtail) ureteric catheter insertions: a retrospective review.
      Pryor (1991)
      • Pryor J.L.
      • Langley M.J.
      • Jenkins A.D.
      Comparison of symptom characteristics of indwelling ureteral catheters.
      El-Nahas (2006)
      • El-Nahas A.R.
      • El-Assmy A.M.
      • Shoma A.M.
      • Eraky I.
      • El-Kenawy M.R.
      • El-Kappany H.A.
      Self-retaining ureteral stents: analysis of factors responsible for patients’ discomfort.
      Gadzhiev (2020)
      • Gadzhiev N.
      • Gorelov D.
      • Malkhasyan V.
      • et al.
      Comparison of silicone versus polyurethane ureteral stents: a prospective controlled study.
      The symbol indicates a low risk of bias, indicates a moderate risk of bias, and indicates a serious risk of bias.
      Our original intention was to perform a pooled data analysis and meta-analysis after collection of all the data from the eligible studies. However, there was a substantial degree of heterogeneity among the studies in terms of both design and outcomes, so the analysis was limited to a narrative synthesis of the results.

      3. Evidence synthesis

      A total of 13 studies assessing the impact of stent material on stent-related symptoms were included in our review [
      • Lennon G.M.
      • Thornhill J.A.
      • Sweeney P.A.
      • Grainger R.
      • McDermott T.E.
      • Butler M.R.
      ‘Firm’ versus ‘soft’ double pigtail ureteric stents: a randomised blind comparative trial.
      ,
      • Joshi H.B.
      • Chitale S.V.
      • Nagarajan M.
      • et al.
      A prospective randomized single-blind comparison of ureteral stents composed of firm and soft polymer.
      ,
      • Candela J.V.
      • Bellman G.C.
      Ureteral stents: impact of diameter and composition on patient symptoms.
      ,
      • Lee C.
      • Kuskowski M.
      • Premoli J.
      • Skemp N.
      • Monga M.
      Randomized evaluation of ureteral stents using validated symptom questionnaire.
      ,
      • Mendez-Probst C.E.
      • Goneau L.W.
      • MacDonald K.W.
      • et al.
      The use of triclosan eluting stents effectively reduces ureteral stent symptoms: a prospective randomized trial.
      ,
      • El-Nahas A.R.
      • Lachine M.
      • Elsawy E.
      • Mosbah A.
      • El-Kappany H.
      A randomized controlled trial comparing antimicrobial (silver sulfadiazine)-coated ureteral stents with non-coated stents.
      ,
      • Wiseman O.
      • Ventimiglia E.
      • Doizi S.
      • et al.
      Effects of silicone hydrocoated double loop ureteral stent on symptoms and quality of life in patients undergoing flexible ureteroscopy for kidney stone: a randomized multicenter clinical study.
      ,
      • Smedley F.H.
      • Rimmer J.
      • Taube M.
      • Edwards L.
      168 double J (pigtail) ureteric catheter insertions: a retrospective review.
      ,
      • Pryor J.L.
      • Langley M.J.
      • Jenkins A.D.
      Comparison of symptom characteristics of indwelling ureteral catheters.
      ,
      • El-Nahas A.R.
      • El-Assmy A.M.
      • Shoma A.M.
      • Eraky I.
      • El-Kenawy M.R.
      • El-Kappany H.A.
      Self-retaining ureteral stents: analysis of factors responsible for patients’ discomfort.
      ,
      • Gadzhiev N.
      • Gorelov D.
      • Malkhasyan V.
      • et al.
      Comparison of silicone versus polyurethane ureteral stents: a prospective controlled study.
      ,
      • Cadieux P.A.
      • Chew B.H.
      • Nott L.
      • et al.
      Use of triclosan-eluting ureteral stents in patients with long-term stents.
      ,
      • Chow P.M.
      • Chiang I.N.
      • Chen C.Y.
      • et al.
      Malignant ureteral obstruction: functional duration of metallic versus polymeric ureteral stents.
      ]. The studies and their main characteristics are summarized in Table 2.
      All the stent materials that were compared are listed in Table 2 and Table 4. Table 4 provides information on the composition and commercial name of all the stents compared in the 13 studies. The number of patients included ranged from 8 to 155 per study. All the stents were DJ stents. The material most often used was Percuflex (Table 4). If specified, most of the DJ stents had a hydrogel coating, but the presence of a coating was not always specified by the author or manufacturer. The DJ stent diameter most frequently used was 6 Fr and the average length was 22–26 cm. The stent indwelling time ranged from 7 d to 366 d (Table 2), with high within-study heterogeneity. The time between DJ stent insertion and evaluation of stent-related symptoms also differed highly between studies. The Ureteral Stent Symptom Questionnaire (USSQ) to evaluate symptoms and the impact on quality of life of ureteral stents, developed by Joshi et al in 2003 [
      • Joshi H.B.
      • Newns N.
      • Stainthorpe A.
      • MacDonagh R.P.
      • Keeley Jr, F.X.
      • Timoney A.G.
      Ureteral stent symptom questionnaire: development and validation of a multidimensional quality of life measure.
      ], was used in four of the nine studies published after 2003 [
      • Joshi H.B.
      • Chitale S.V.
      • Nagarajan M.
      • et al.
      A prospective randomized single-blind comparison of ureteral stents composed of firm and soft polymer.
      ,
      • Lee C.
      • Kuskowski M.
      • Premoli J.
      • Skemp N.
      • Monga M.
      Randomized evaluation of ureteral stents using validated symptom questionnaire.
      ,
      • El-Nahas A.R.
      • Lachine M.
      • Elsawy E.
      • Mosbah A.
      • El-Kappany H.
      A randomized controlled trial comparing antimicrobial (silver sulfadiazine)-coated ureteral stents with non-coated stents.
      ,
      • Wiseman O.
      • Ventimiglia E.
      • Doizi S.
      • et al.
      Effects of silicone hydrocoated double loop ureteral stent on symptoms and quality of life in patients undergoing flexible ureteroscopy for kidney stone: a randomized multicenter clinical study.
      ]. When the USSQ was not used as a symptom evaluation tool, studies used the Visual Analog Scale for Pain (VASP), the overactive bladder (OAB) awareness tool or self-made questionnaires [
      • Lennon G.M.
      • Thornhill J.A.
      • Sweeney P.A.
      • Grainger R.
      • McDermott T.E.
      • Butler M.R.
      ‘Firm’ versus ‘soft’ double pigtail ureteric stents: a randomised blind comparative trial.
      ,
      • Candela J.V.
      • Bellman G.C.
      Ureteral stents: impact of diameter and composition on patient symptoms.
      ,
      • Mendez-Probst C.E.
      • Goneau L.W.
      • MacDonald K.W.
      • et al.
      The use of triclosan eluting stents effectively reduces ureteral stent symptoms: a prospective randomized trial.
      ,
      • Smedley F.H.
      • Rimmer J.
      • Taube M.
      • Edwards L.
      168 double J (pigtail) ureteric catheter insertions: a retrospective review.
      ,
      • Pryor J.L.
      • Langley M.J.
      • Jenkins A.D.
      Comparison of symptom characteristics of indwelling ureteral catheters.
      ,
      • El-Nahas A.R.
      • El-Assmy A.M.
      • Shoma A.M.
      • Eraky I.
      • El-Kenawy M.R.
      • El-Kappany H.A.
      Self-retaining ureteral stents: analysis of factors responsible for patients’ discomfort.
      ,
      • Gadzhiev N.
      • Gorelov D.
      • Malkhasyan V.
      • et al.
      Comparison of silicone versus polyurethane ureteral stents: a prospective controlled study.
      ,
      • Cadieux P.A.
      • Chew B.H.
      • Nott L.
      • et al.
      Use of triclosan-eluting ureteral stents in patients with long-term stents.
      ,
      • Chow P.M.
      • Chiang I.N.
      • Chen C.Y.
      • et al.
      Malignant ureteral obstruction: functional duration of metallic versus polymeric ureteral stents.
      ]. Seven articles reported on prospective randomized studies (Table 1, Table 2) but only one can be classified as a high-quality study with low risk of bias [
      • Wiseman O.
      • Ventimiglia E.
      • Doizi S.
      • et al.
      Effects of silicone hydrocoated double loop ureteral stent on symptoms and quality of life in patients undergoing flexible ureteroscopy for kidney stone: a randomized multicenter clinical study.
      ]. Three reports were on prospective cohort studies, two studies were self-controlled case series, and one study was retrospective (Table 2). Of the 13 studies, nine focused on the core composition material of the stent, while four focused on stent coating (Table 2).
      Table 4Stent materials and commercial names
      Limited to the materials and commercial names for stents used in the studies included in the review.
      MaterialClassChemical compositionManufacturer and commercial name
      SiliconeSiliconeCondensation polymer comprising chains of alternating silicon and oxygen atoms
      • Mardis H.K.
      • Kroeger R.M.
      • Morton J.J.
      • Donovan J.M.
      Comparative evaluation of materials used for internal ureteral stents.
      Cook Black silicone



      Coloplast ImaJin Hydro

      Coloplast (Porges S.A.) silicone
      SilitekSilicone + polyesterProprietary modified silicone based polyester block copolymer
      • Liatsikos E.
      • Kallidonis P.
      • Stolzenburg J.U.
      • Karnabatidis D.
      Ureteral stents: past, present and future.
      ,
      • Venkatesan N.
      • Shroff S.
      • Jayachandran K.
      • Doble M.
      Polymers as ureteral stents.
      ,
      • Mardis H.K.
      • Kroeger R.M.
      • Morton J.J.
      • Donovan J.M.
      Comparative evaluation of materials used for internal ureteral stents.
      ,
      • Hendlin K.
      • Dockendorf K.
      • Horn C.
      • Pshon N.
      • Lund B.
      • Monga M.
      Ureteral stents: coil strength and durometer.
      Surgitek Silitek
      C-FlexSilicone + polyolefinSilicone-modified styrene/ethylene/butylene thermoplastic block copolymer
      • Mardis H.K.
      • Kroeger R.M.
      • Morton J.J.
      • Donovan J.M.
      Comparative evaluation of materials used for internal ureteral stents.
      ,
      • Hendlin K.
      • Dockendorf K.
      • Horn C.
      • Pshon N.
      • Lund B.
      • Monga M.
      Ureteral stents: coil strength and durometer.
      Cook C-Flex

      Van-Tec “Soft”
      PercuflexPolyolefinProprietary thermoplastic olefinic block copolymer
      • Liatsikos E.
      • Kallidonis P.
      • Stolzenburg J.U.
      • Karnabatidis D.
      Ureteral stents: past, present and future.
      ,
      • Venkatesan N.
      • Shroff S.
      • Jayachandran K.
      • Doble M.
      Polymers as ureteral stents.
      ,
      • Hendlin K.
      • Dockendorf K.
      • Horn C.
      • Pshon N.
      • Lund B.
      • Monga M.
      Ureteral stents: coil strength and durometer.
      Boston (Microvasive)

      – Percuflex

      – Percuflex Plus (“firm” Percuflex + Hydroplus
      Proprietary hydrogel by Boston Scientific.
      )

      – Contour (“soft” Percuflex + Hydroplus
      Proprietary hydrogel by Boston Scientific.
      )
      Polyurethane (standard)PolyurethaneLinear polymer of urethane units with a backbone that contains carbamate groups ( NHCO2). The links are produced via chemical reaction between a di-isocyanate and a polyol
      • Venkatesan N.
      • Shroff S.
      • Jayachandran K.
      • Doble M.
      Polymers as ureteral stents.
      Cook polyurethane

      Rüsch (Teleflex) polyurethane
      Sof-FlexPolyurethaneProprietary modified polyurethane-based polymer with hydrogel
      • Venkatesan N.
      • Shroff S.
      • Jayachandran K.
      • Doble M.
      Polymers as ureteral stents.
      Cook Sof-Flex
      TecoflexPolyurethaneModified polyurethane-based aliphatic thermoplastic; product of the reaction between methylene-bis(cyclohexyl)-di-isocyanate, poly(tetramethylene ether glycol), and 1,4-butanediol
      • Liatsikos E.
      • Kallidonis P.
      • Stolzenburg J.U.
      • Karnabatidis D.
      Ureteral stents: past, present and future.
      ,
      • Venkatesan N.
      • Shroff S.
      • Jayachandran K.
      • Doble M.
      Polymers as ureteral stents.
      ,
      • Hendlin K.
      • Dockendorf K.
      • Horn C.
      • Pshon N.
      • Lund B.
      • Monga M.
      Ureteral stents: coil strength and durometer.
      Surgitek Classic
      CarbothanePolyurethaneProprietary modified polyurethane-based polymerAmecath Carbothane
      PellethanePolyurethane + fluoropolymerProprietary modified polyurethane-based mixture of PTFE and proprietary materials
      • Liatsikos E.
      • Kallidonis P.
      • Stolzenburg J.U.
      • Karnabatidis D.
      Ureteral stents: past, present and future.
      Bard Inlay (Pellethane with pHreeCoat
      Proprietary hydrogel with pH-stabilizing capabilities.
      )
      • Liatsikos E.
      • Kallidonis P.
      • Stolzenburg J.U.
      • Karnabatidis D.
      Ureteral stents: past, present and future.
      Endo-SofProprietaryProprietary compoundCook Endo-Sof
      VertexProprietaryProprietary compoundApplied Medical Vertex
      ResonanceMetalNickel‐cobalt‐chromium‐molybdenum alloy
      • Liatsikos E.
      • Kallidonis P.
      • Stolzenburg J.U.
      • Karnabatidis D.
      Ureteral stents: past, present and future.
      Cook Resonance
      TriclosanAntimicrobialTriclosanTriumph triclosan-eluting stent
      Silver sulfadiazineAntimicrobialSilver sulfadiazineAmecath Carbothane with silver sulfadiazine
      PTFE = polytetrafluoroethylene.
      a Limited to the materials and commercial names for stents used in the studies included in the review.
      b Proprietary hydrogel by Boston Scientific.
      c Proprietary hydrogel with pH-stabilizing capabilities.

      3.1 Core composition

      In 1988, Smedley et al. [
      • Smedley F.H.
      • Rimmer J.
      • Taube M.
      • Edwards L.
      168 double J (pigtail) ureteric catheter insertions: a retrospective review.
      ] were the first group to examine the impact of core composition on stent-related symptoms in a comparison of “hard” (polyurethane) versus “soft” (silicone) DJ stents. The authors noted less loin discomfort (24% vs 18%) and less trigonal irritation (29% vs. 18%) in favor of the “soft” silicone stent, although the difference was not significant. Limitations of this study were its heterogeneity in terms of inclusion criteria, stent removal date, and time points for symptom evaluation. There was also no information on the stent manufacturers, eventual coatings, and stent length or width. Lastly, the study was limited by its retrospective nature.
      Lennon et al. [
      • Lennon G.M.
      • Thornhill J.A.
      • Sweeney P.A.
      • Grainger R.
      • McDermott T.E.
      • Butler M.R.
      ‘Firm’ versus ‘soft’ double pigtail ureteric stents: a randomised blind comparative trial.
      ] also compared “hard” (Cook polyurethane) and “soft” (Cook Sof-Flex) DJ stents. Results for the stent-related domains of renal pain (58% vs 38%), suprapubic pain (46% vs 26%), dysuria (40% vs 23%), and continuation of normal life activity (45% vs 67%) were all significantly better among patients with the “soft” stent. In addition, reflux-type pain, daytime frequency, urgency, nocturia, and hematuria were less frequent with the “soft” stent, but the differences were not statistically significant. Although none of the patients were completely free of symptoms, the overall severity of stent-related symptoms was clearly lower in the “soft” stent group. Limitations of this study include unclear inclusion criteria and extreme heterogeneity for the time points for symptom evaluation. In addition, the USSQ was not used and no information about the randomization process or missing outcome data was provided.
      Lee et al. [
      • Lee C.
      • Kuskowski M.
      • Premoli J.
      • Skemp N.
      • Monga M.
      Randomized evaluation of ureteral stents using validated symptom questionnaire.
      ] evaluated stent-related symptoms for five different 6Fr DJ stents: Bard Inlay, Cook Endo-Sof, Boston Scientific Contour, Applied Medical Vertex and Surgitek Classic. The authors found a significant difference in total USSQ symptom scores on day 3 in favor of the Bard Inlay stent, but the difference was not statistically significant on days 1 and 5. Regarding individual symptoms, significantly fewer patients in the Bard Inlay group reported hematuria, sleep disturbance, a need for analgesia, flank pain, and groin pain. Patients in this group also showed greater patient independence on days 1, 3, and/or 5 in comparison to the other DJ stents examined. The Applied Medical Vertex and Surgitek Classic DJ stents were associated with the most significant symptoms: the Vertex stent causing more groin pain on day 1, more frequency and nocturia on day 3, and necessitated more narcotic use on day 5 in comparison to the other four DJ stents. The Surgitek Classic DJ stent caused more hematuria on days 1 and 3 and more flank pain on day 1. Limitations of this study include the low number of patients (only 44 patients completed the study, to compare five DJ stents), heterogeneous inclusion criteria, and no specification of the stent indwelling time or time points for symptom evaluation. Lastly, no information was given about the randomization process or missing outcome data, as it was noted that only 44 of 70 patients completed the study.
      El-Nahas et al. [
      • El-Nahas A.R.
      • El-Assmy A.M.
      • Shoma A.M.
      • Eraky I.
      • El-Kenawy M.R.
      • El-Kappany H.A.
      Self-retaining ureteral stents: analysis of factors responsible for patients’ discomfort.
      ] compared a “soft” (Coloplast silicone) DJ stent to a “hard” (Boston Scientific Percuflex) DJ stent. They reported significantly more stent-related symptoms for patients with the “hard” stent (46% vs 75%). Limitations of this study are heterogeneity in inclusion criteria, heterogeneity in stent width, and most notably extreme heterogeneity in the time points for symptom evaluation. Lastly, the USSQ was not used and no information on missing outcome data was provided.
      Gadzhiev et al. [
      • Gadzhiev N.
      • Gorelov D.
      • Malkhasyan V.
      • et al.
      Comparison of silicone versus polyurethane ureteral stents: a prospective controlled study.
      ] compared ureteral stent-related symptoms between the Cook Black Silicone and Rüsch polyurethane DJ stents in terms of VASP and OAB awareness tool results at days 1, 14, and 28 (with an indwelling time of 28 d). Silicone DJ stents were associated with significantly lower pain intensity assessed using VASP at days 14 and 28. Limitations of this study were failure to use the USSQ, the nonrandomized design, and the lack of information regarding missing data.
      In the most recent and highest-quality study, Wiseman et al. [
      • Wiseman O.
      • Ventimiglia E.
      • Doizi S.
      • et al.
      Effects of silicone hydrocoated double loop ureteral stent on symptoms and quality of life in patients undergoing flexible ureteroscopy for kidney stone: a randomized multicenter clinical study.
      ] compared the Coloplast ImaJin Hydro silicone DJ stent to the Boston Scientific Percuflex Plus stent after flexible ureteroscopy for renal stones between 5 and 25 mm. The silicone DJ stents were associated with significantly less patient discomfort and better quality of life in comparison to the nonsilicone polymer DJ stent. The authors observed a 25% reduction in USSQ pain score at day 20 and significantly lower urinary symptoms (as for the relative USSQ domain) at days 2, 7, and 20, with the greatest difference at day 20, all in favor of the silicone DJ stent. Limitations of the study are the nonstandardized medical therapy and a notably high dropout rate, although this was methodologically handled correctly.

      3.2 Coating

      Cadieux et al. [
      • Cadieux P.A.
      • Chew B.H.
      • Nott L.
      • et al.
      Use of triclosan-eluting ureteral stents in patients with long-term stents.
      ] investigated the clinical benefit of triclosan-eluting (antimicrobial) stents on urine and stent cultures as a primary aim. Although the authors did not observe a clear benefit in terms of urine and stent cultures, they did note significantly fewer symptomatic infections. Therefore, Mendez-Probst et al. [
      • Mendez-Probst C.E.
      • Goneau L.W.
      • MacDonald K.W.
      • et al.
      The use of triclosan eluting stents effectively reduces ureteral stent symptoms: a prospective randomized trial.
      ] conducted a new study to compare a regular hydrogel-coated DJ stent (Boston Scientific Percuflex Plus) to a Triumph triclosan-eluting DJ stent, with a focus on stent-related symptoms. In general, the results indicated less discomfort during micturition and movement in favor of the triclosan-eluting stent. More specifically, the triclosan-eluting DJ stent was associated with significantly less flank pain during activity, less painful micturition, and less abdominal pain during activity. Limitations of this study were the low number of patients (n = 20), failure to use the USSQ, heterogeneous inclusion criteria, and no information about the randomization process.
      Two out of four studies on coating, and three out of nine studies on core composition showed no difference in the impact of DJ stent material on stent-related symptoms [
      • Joshi H.B.
      • Chitale S.V.
      • Nagarajan M.
      • et al.
      A prospective randomized single-blind comparison of ureteral stents composed of firm and soft polymer.
      ,
      • Candela J.V.
      • Bellman G.C.
      Ureteral stents: impact of diameter and composition on patient symptoms.
      ,
      • El-Nahas A.R.
      • Lachine M.
      • Elsawy E.
      • Mosbah A.
      • El-Kappany H.
      A randomized controlled trial comparing antimicrobial (silver sulfadiazine)-coated ureteral stents with non-coated stents.
      ,
      • Pryor J.L.
      • Langley M.J.
      • Jenkins A.D.
      Comparison of symptom characteristics of indwelling ureteral catheters.
      ,
      • Chow P.M.
      • Chiang I.N.
      • Chen C.Y.
      • et al.
      Malignant ureteral obstruction: functional duration of metallic versus polymeric ureteral stents.
      ]. Limitations were the lack of information on DJ stent length and width, low patient numbers, heterogeneous inclusion criteria, very heterogeneous dwell times, lack of USSQ use, and high risk of bias (Table 2 and Supplementary material).

      3.3 Discussion

      Five out of nine studies on core composition found that the material of a DJ stent has an impact on stent-related symptoms [
      • Lennon G.M.
      • Thornhill J.A.
      • Sweeney P.A.
      • Grainger R.
      • McDermott T.E.
      • Butler M.R.
      ‘Firm’ versus ‘soft’ double pigtail ureteric stents: a randomised blind comparative trial.
      ,
      • Lee C.
      • Kuskowski M.
      • Premoli J.
      • Skemp N.
      • Monga M.
      Randomized evaluation of ureteral stents using validated symptom questionnaire.
      ,
      • Wiseman O.
      • Ventimiglia E.
      • Doizi S.
      • et al.
      Effects of silicone hydrocoated double loop ureteral stent on symptoms and quality of life in patients undergoing flexible ureteroscopy for kidney stone: a randomized multicenter clinical study.
      ,
      • El-Nahas A.R.
      • El-Assmy A.M.
      • Shoma A.M.
      • Eraky I.
      • El-Kenawy M.R.
      • El-Kappany H.A.
      Self-retaining ureteral stents: analysis of factors responsible for patients’ discomfort.
      ,
      • Gadzhiev N.
      • Gorelov D.
      • Malkhasyan V.
      • et al.
      Comparison of silicone versus polyurethane ureteral stents: a prospective controlled study.
      ]. Of the four studies comparing nonsilicone polymers to silicone, three found that silicone significantly reduces stent-related symptoms [
      • Wiseman O.
      • Ventimiglia E.
      • Doizi S.
      • et al.
      Effects of silicone hydrocoated double loop ureteral stent on symptoms and quality of life in patients undergoing flexible ureteroscopy for kidney stone: a randomized multicenter clinical study.
      ,
      • El-Nahas A.R.
      • El-Assmy A.M.
      • Shoma A.M.
      • Eraky I.
      • El-Kenawy M.R.
      • El-Kappany H.A.
      Self-retaining ureteral stents: analysis of factors responsible for patients’ discomfort.
      ,
      • Gadzhiev N.
      • Gorelov D.
      • Malkhasyan V.
      • et al.
      Comparison of silicone versus polyurethane ureteral stents: a prospective controlled study.
      ]. The study of highest quality also favored silicone with a hydrogel coating over a nonsilicone polymer with a hydrogel coating [
      • Wiseman O.
      • Ventimiglia E.
      • Doizi S.
      • et al.
      Effects of silicone hydrocoated double loop ureteral stent on symptoms and quality of life in patients undergoing flexible ureteroscopy for kidney stone: a randomized multicenter clinical study.
      ]. Of the five studies comparing only nonsilicone polymers, two favored the Bard Inlay and Cook Medical Sof-Flex DJ stents [
      • Lennon G.M.
      • Thornhill J.A.
      • Sweeney P.A.
      • Grainger R.
      • McDermott T.E.
      • Butler M.R.
      ‘Firm’ versus ‘soft’ double pigtail ureteric stents: a randomised blind comparative trial.
      ,
      • Lee C.
      • Kuskowski M.
      • Premoli J.
      • Skemp N.
      • Monga M.
      Randomized evaluation of ureteral stents using validated symptom questionnaire.
      ].
      In general, the results suggest that silicone DJ stents do reduce stent-related symptoms. In addition, since it is stated that the Bard Inlay and Cook Sof-Flex DJ stents are relatively “soft”, it seems that all DJ stents associated with a reduction in stent-related symptoms were “soft” or “flexible” [
      • Mardis H.K.
      • Kroeger R.M.
      • Morton J.J.
      • Donovan J.M.
      Comparative evaluation of materials used for internal ureteral stents.
      ,
      • Hendlin K.
      • Dockendorf K.
      • Horn C.
      • Pshon N.
      • Lund B.
      • Monga M.
      Ureteral stents: coil strength and durometer.
      ]. Multiple problems when trying to answer the review question arose during this systematic review. The main issue is the difficulty in proving an association between chemical or physical stent material properties and clinical impact. First, some manufactures release very little information about stent composition. Table 4 shows that most of the DJ stents were made of proprietary material of undisclosed composition. Second, there is no established “standard” for how physical stent properties are measured, denominated, and used in clinical studies. Taking the most important factors, for example, “stiffness” and “hardness” were used interchangeably but they are not necessarily the same [
      • Lennon G.M.
      • Thornhill J.A.
      • Sweeney P.A.
      • Grainger R.
      • McDermott T.E.
      • Butler M.R.
      ‘Firm’ versus ‘soft’ double pigtail ureteric stents: a randomised blind comparative trial.
      ,
      • Venkatesan N.
      • Shroff S.
      • Jayachandran K.
      • Doble M.
      Polymers as ureteral stents.
      ,
      • Mosayyebi A.
      • Manes C.
      • Carugo D.
      • Somani B.K.
      Advances in ureteral stent design and materials.
      ,
      • Joshi H.B.
      • Chitale S.V.
      • Nagarajan M.
      • et al.
      A prospective randomized single-blind comparison of ureteral stents composed of firm and soft polymer.
      ,
      • Hendlin K.
      • Dockendorf K.
      • Horn C.
      • Pshon N.
      • Lund B.
      • Monga M.
      Ureteral stents: coil strength and durometer.
      ,
      • Thomas R.
      Indwelling ureteral stents: impact of material and shape on patient comfort.
      ]. To measure “hardness”, some studies used the American Society for Testing and Materials D2240 standard, which measures indentation hardness (Shore hardness) with durometer as the unit of measure [
      • Lennon G.M.
      • Thornhill J.A.
      • Sweeney P.A.
      • Grainger R.
      • McDermott T.E.
      • Butler M.R.
      ‘Firm’ versus ‘soft’ double pigtail ureteric stents: a randomised blind comparative trial.
      ,
      • Venkatesan N.
      • Shroff S.
      • Jayachandran K.
      • Doble M.
      Polymers as ureteral stents.
      ,
      • Joshi H.B.
      • Chitale S.V.
      • Nagarajan M.
      • et al.
      A prospective randomized single-blind comparison of ureteral stents composed of firm and soft polymer.
      ]. The force in grams required to flex the stent coil by 90° is used as a measure of “stiffness” or “flexibility” [
      • Lennon G.M.
      • Thornhill J.A.
      • Sweeney P.A.
      • Grainger R.
      • McDermott T.E.
      • Butler M.R.
      ‘Firm’ versus ‘soft’ double pigtail ureteric stents: a randomised blind comparative trial.
      ]. Others used Young’s modulus of elasticity, a measure of tensile strength, and converted it to stiffness and hardness, with durometer as the unit of measure [
      • Hendlin K.
      • Dockendorf K.
      • Horn C.
      • Pshon N.
      • Lund B.
      • Monga M.
      Ureteral stents: coil strength and durometer.
      ]. As a result, the measurements reported for “stiffness” and “flexibility” are variable and subject to interpretation [
      • Lennon G.M.
      • Thornhill J.A.
      • Sweeney P.A.
      • Grainger R.
      • McDermott T.E.
      • Butler M.R.
      ‘Firm’ versus ‘soft’ double pigtail ureteric stents: a randomised blind comparative trial.
      ,
      • Mardis H.K.
      • Kroeger R.M.
      • Morton J.J.
      • Donovan J.M.
      Comparative evaluation of materials used for internal ureteral stents.
      ,
      • Joshi H.B.
      • Chitale S.V.
      • Nagarajan M.
      • et al.
      A prospective randomized single-blind comparison of ureteral stents composed of firm and soft polymer.
      ,
      • Hendlin K.
      • Dockendorf K.
      • Horn C.
      • Pshon N.
      • Lund B.
      • Monga M.
      Ureteral stents: coil strength and durometer.
      ]. It is also clear that just mentioning “silicone” or “polyurethane” is not sufficient, as physical properties differ between manufacturers using the “same” material, meaning that not every silicone stent is made equally [
      • Mardis H.K.
      • Kroeger R.M.
      • Morton J.J.
      • Donovan J.M.
      Comparative evaluation of materials used for internal ureteral stents.
      ]. Of the nine studies evaluating core material, only two examined the physical properties of the DJ stents they used and specified these properties in measurement units [
      • Lennon G.M.
      • Thornhill J.A.
      • Sweeney P.A.
      • Grainger R.
      • McDermott T.E.
      • Butler M.R.
      ‘Firm’ versus ‘soft’ double pigtail ureteric stents: a randomised blind comparative trial.
      ,
      • Joshi H.B.
      • Chitale S.V.
      • Nagarajan M.
      • et al.
      A prospective randomized single-blind comparison of ureteral stents composed of firm and soft polymer.
      ]. Lastly, it is concerning that even if measurement and denomination standards existed, Hendlin et al. [
      • Hendlin K.
      • Dockendorf K.
      • Horn C.
      • Pshon N.
      • Lund B.
      • Monga M.
      Ureteral stents: coil strength and durometer.
      ] showed that there can be statistically significant variability in durometer results between different lot numbers for stents made by the same manufacturer. If confirmed by other studies, this batch variability increases the complexity in understanding why a particular stent material results in fewer stent-related symptoms.
      Stent coatings are another part of the puzzle. The most common coating is hydrogel, consisting of hydrophilic polymers that reduce the friction coefficient, thereby facilitating stent placement and potentially increasing patient comfort [
      • Chew B.H.
      • Denstedt J.D.
      Technology insight: novel ureteral stent materials and designs.
      ]. Only one study specifically compared DJ stents with and without a hydrogel with regard to stent-related symptoms and found no significant difference [
      • Candela J.V.
      • Bellman G.C.
      Ureteral stents: impact of diameter and composition on patient symptoms.
      ]. Other studies researching the impact of DJ stent coating on stent-related symptoms examined the effect of an anti-microbial coating. The findings show that a triclosan coating resulted in significantly less discomfort, while no such benefit was observed for a silver sulfadiazine coating [
      • Mendez-Probst C.E.
      • Goneau L.W.
      • MacDonald K.W.
      • et al.
      The use of triclosan eluting stents effectively reduces ureteral stent symptoms: a prospective randomized trial.
      ,
      • El-Nahas A.R.
      • Lachine M.
      • Elsawy E.
      • Mosbah A.
      • El-Kappany H.
      A randomized controlled trial comparing antimicrobial (silver sulfadiazine)-coated ureteral stents with non-coated stents.
      ,
      • Cadieux P.A.
      • Chew B.H.
      • Nott L.
      • et al.
      Use of triclosan-eluting ureteral stents in patients with long-term stents.
      ]. Nevertheless, since only one study was conducted per coating, no conclusion can be drawn.
      Hypotheses on why silicone DJ stents might reduce stent-related symptoms often mention the softness, flexibility, biologic inertness, and low encrustation and bacterial adhesion rates of silicone [
      • Liatsikos E.
      • Kallidonis P.
      • Stolzenburg J.U.
      • Karnabatidis D.
      Ureteral stents: past, present and future.
      ,
      • Venkatesan N.
      • Shroff S.
      • Jayachandran K.
      • Doble M.
      Polymers as ureteral stents.
      ,
      • Mardis H.K.
      • Kroeger R.M.
      • Morton J.J.
      • Donovan J.M.
      Comparative evaluation of materials used for internal ureteral stents.
      ,
      • Mosayyebi A.
      • Manes C.
      • Carugo D.
      • Somani B.K.
      Advances in ureteral stent design and materials.
      ,
      • Beiko D.T.
      • Knudsen B.E.
      • Denstedt J.D.
      Advances in ureteral stent design.
      ]. It is suspected that higher encrustation and bacterial adhesion rates, related to a longer indwelling time, have a negative impact on stent-related symptoms [
      • Mosayyebi A.
      • Manes C.
      • Carugo D.
      • Somani B.K.
      Advances in ureteral stent design and materials.
      ,
      • Koprowski C.
      • Kim C.
      • Modi P.K.
      • Elsamra S.E.
      Ureteral stent-associated pain: a review.
      ,
      • Kawahara T.
      • Ito H.
      • Terao H.
      • Yoshida M.
      • Matsuzaki J.
      Ureteral stent encrustation, incrustation, and coloring: morbidity related to indwelling times.
      ]. Comparing silicone to a nonsilicone polymer, most studies reported less encrustation and bacterial adhesion in favor of silicone [
      • Barghouthy Y.
      • Wiseman O.
      • Ventimiglia E.
      • et al.
      Silicone-hydrocoated ureteral stents encrustation and biofilm formation after 3-week dwell time: results of a prospective randomized multicenter clinical study.
      ,
      • Watterson J.D.
      • Cadieux P.A.
      • Stickler D.
      • Reid G.
      • Denstedt J.D.
      Swarming of Proteus mirabilis over ureteral stents: a comparative assessment.
      ,
      • Tunney M.M.
      • Keane P.F.
      • Jones D.S.
      • Gorman S.P.
      Comparative assessment of ureteral stent biomaterial encrustation.
      ,
      • Desgrandchamps F.
      • Moulinier F.
      • Daudon M.
      • Teillac P.
      • Le Duc A.
      An in vitro comparison of urease-induced encrustation of JJ stents in human urine.
      ]. However, the importance of coatings should not be overlooked. When a noncoated silicone DJ stent was compared to a hydrocoated silicone DJ stent, encrustation appeared to be more severe on the noncoated stent [
      • Cormio L.
      • Talja M.
      • Koivusalo A.
      • Mäkisalo H.
      • Wolff H.
      • Ruutu M.
      Biocompatibility of various indwelling double-J stents.
      ]. In general, however, the evidence is heterogeneous, with hydrogel coating seeming to both reduce and increase encrustation and biofilm formation [
      • Chew B.H.
      • Denstedt J.D.
      Technology insight: novel ureteral stent materials and designs.
      ,
      • Desgrandchamps F.
      • Moulinier F.
      • Daudon M.
      • Teillac P.
      • Le Duc A.
      An in vitro comparison of urease-induced encrustation of JJ stents in human urine.
      ,
      • Gorman S.P.
      • Tunney M.M.
      • Keane P.F.
      • Van Bladel K.
      • Bley B.
      Characterization and assessment of a novel poly(ethylene oxide)/polyurethane composite hydrogel (Aquavene) as a ureteral stent biomaterial.
      ]. Since a hydrogel coating might influence stent-related symptoms in various ways, subdifferentiation between studies on core composition would be desirable to compare DJ stents without a hydrogel coating (“true” core composition) and DJ stents with a hydrogel coating (combined core composition and coating). However, since more than half of the core composition studies failed to clarify whether or not the stents compared had a hydrogel coating, this differentiation could not be made (Table 2). This makes it even more difficult to draw a conclusion regarding the impact of DJ stent core material on stent-related symptoms.
      Studies used in this review varied widely in their methods; the most important variations were in the inclusion and exclusion criteria, the symptom assessments, and the dwell time. First, the inclusion and exclusion criteria differed between some studies that only allowed specific types of stone disease and others that allowed a wide variety of indications. This could possibly have an impact on the results. Second, the method used to assess stent-related symptoms is of utmost importance. Although the USSQ was validated and introduced in 2003, only four of nine studies published after 2003 used this questionnaire for symptom assessment. The USSQ is generally considered a validated and superior tool for assessment of stent-related symptoms [
      • Joshi H.B.
      • Chitale S.V.
      • Nagarajan M.
      • et al.
      A prospective randomized single-blind comparison of ureteral stents composed of firm and soft polymer.
      ,
      • Wiseman O.
      • Ventimiglia E.
      • Doizi S.
      • et al.
      Effects of silicone hydrocoated double loop ureteral stent on symptoms and quality of life in patients undergoing flexible ureteroscopy for kidney stone: a randomized multicenter clinical study.
      ,
      • Joshi H.B.
      • Newns N.
      • Stainthorpe A.
      • MacDonagh R.P.
      • Keeley Jr, F.X.
      • Timoney A.G.
      Ureteral stent symptom questionnaire: development and validation of a multidimensional quality of life measure.
      ]. Lastly, very heterogeneous dwell times and different time frames for patient evaluation were noted [
      • Lee C.
      • Kuskowski M.
      • Premoli J.
      • Skemp N.
      • Monga M.
      Randomized evaluation of ureteral stents using validated symptom questionnaire.
      ,
      • Wiseman O.
      • Ventimiglia E.
      • Doizi S.
      • et al.
      Effects of silicone hydrocoated double loop ureteral stent on symptoms and quality of life in patients undergoing flexible ureteroscopy for kidney stone: a randomized multicenter clinical study.
      ,
      • Gadzhiev N.
      • Gorelov D.
      • Malkhasyan V.
      • et al.
      Comparison of silicone versus polyurethane ureteral stents: a prospective controlled study.
      ]. The dwell time also varied widely within the studies: the average overall DJ stent indwelling time was a relatively long period of 27 d and the range was 7–366 d (Table 2), while most urologists normally favor a dwell time of 1–2 wk after ureteroscopy. Unfortunately, since the studies we included had very heterogeneous populations, debatable comparability for the intervention comparisons, and no outcome with comparable methodology, it was not possible to conduct any pooled analysis or meta-analysis for these data. Second, there was only one high-quality study with a low risk of bias. It has been suggested that high-quality studies may be superior to meta-analyses based on low-quality data. When there is a conflict between high-quality randomized trials and meta-analyses, readers should analyze the evidence themselves to decide which offers the best-quality evidence [
      • Sylvester R.J.
      • Canfield S.E.
      • Lam T.B.
      • et al.
      Conflict of evidence: resolving discrepancies when findings from randomized controlled trials and meta-analyses disagree.
      ,
      • De Coninck V.
      • Antonelli J.
      • Chew B.
      • Patterson J.M.
      • Skolarikos A.
      • Bultitude M.
      Medical expulsive therapy for urinary stones: future trends and knowledge gaps.
      ]. Readers should bear in mind that more than one-third of meta-analyses are later discredited after publication of high-quality randomized controlled trials. Therefore, in cases for which there are many low-quality trials among a limited number of high-quality randomized controlled trials, the latter and not meta-analyses are considered the gold standard in the evaluation of therapies [
      • De Coninck V.
      • Antonelli J.
      • Chew B.
      • Patterson J.M.
      • Skolarikos A.
      • Bultitude M.
      Medical expulsive therapy for urinary stones: future trends and knowledge gaps.
      ,
      • LeLorier J.
      • Grégoire G.
      • Benhaddad A.
      • Lapierre J.
      • Derderian F.
      Discrepancies between meta-analyses and subsequent large randomized, controlled trials.
      ].
      Here we focused on the material composition of stents. However, other factors such as DJ stent length, diameter, and positioning, as well as use of medical therapy, may also affect stent-related symptoms [
      • Koprowski C.
      • Kim C.
      • Modi P.K.
      • Elsamra S.E.
      Ureteral stent-associated pain: a review.
      ]. Although evidence on this is mixed, DJ stent length and diameter were relatively comparable between studies (Table 2) [
      • Koprowski C.
      • Kim C.
      • Modi P.K.
      • Elsamra S.E.
      Ureteral stent-associated pain: a review.
      ]. Moreover, the importance of pharmacologic treatment of stent-related symptoms is often omitted since use of medication was not or under-reported in all studies. α-Blockers may reduce the morbidity of DJ stents and increase tolerability, while results for the use of anticholinergics are mixed [
      • Koprowski C.
      • Kim C.
      • Modi P.K.
      • Elsamra S.E.
      Ureteral stent-associated pain: a review.
      ,
      • Wang C.J.
      • Huang S.W.
      • Chang C.H.
      Effects of specific α-1A/1D blocker on lower urinary tract symptoms due to double-J stent: a prospectively randomized study.
      ,
      • Lamb A.D.
      • Vowler S.L.
      • Johnston R.
      • Dunn N.
      • Wiseman O.J.
      Meta-analysis showing the beneficial effect of α-blockers on ureteric stent discomfort.
      ,
      • Betschart P.
      • Zumstein V.
      • Piller A.
      • Schmid H.P.
      • Abt D.
      Prevention and treatment of symptoms associated with indwelling ureteral stents: a systematic review.
      ]. Mirabegron may have a beneficial effect, but the evidence is based on low-quality studies [

      Van Besien J, Keller EX, Somani B, et al. Mirabegron for the treatment of ureteral stent-related symptoms: a systematic review and meta-analysis. Eur Urol Focus. In press. https://doi.org/10.1016/j.euf.2021.10.002.

      ]. A significant improvement in multiple USSQ domains at an early time point can be achieved via pharmacologic intervention [
      • Betschart P.
      • Zumstein V.
      • Piller A.
      • Schmid H.P.
      • Abt D.
      Prevention and treatment of symptoms associated with indwelling ureteral stents: a systematic review.
      ].
      In future research it will be important to establish a standard for measuring and reporting the physical properties of stents to evaluate the impact of stent material composition on stent-related symptoms. If such a standard is established and a reduction in stent-related symptoms is observed, any associations with physical properties could then be identified. Studying the impact of the physical properties of a stent would provide a more feasible framework to draw conclusions and make improvements to implement in clinical practice. An ideal step would be proposal of a validated and standardized measurement unit accepted by both manufacturers and researchers. In addition, uniformity of inclusion and exclusion criteria would facilitate interpretation of study results. These criteria should preferably limit inclusion to DJ stents placed unilaterally and via retrograde access for stone disease in adults. In general, more high-quality, non–industry-sponsored, randomized, prospective, multicenter studies with low risk of bias are needed. Such studies should use the USSQ at well-defined clinically relevant time points (e.g. days 3, 7, 14, and 21). Lastly, knowing that medical therapy can impact on USSQ scores, use of analgesics, nonsteroidal anti-inflammatory drugs, α-blockers, anticholinergics, and mirabegron should be well documented and subsequently analyzed to identify any difference in use between study arms.

      4. Conclusions

      Silicone DJ stents, and by extension “soft” DJ stents, appear to reduce stent-related symptoms in comparison to nonsilicone polymers and “hard” DJ stents. No definitive conclusion can be drawn owing to the lack of high-quality evidence. A standard for measuring and reporting physical stent properties is paramount to carry out effective comparisons between studies and thus identify the stent modifications needed to reduce patient-reported stent-related symptoms.
      Author contributions: Vincent De Coninck had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
      Study concept and design: Boeykens, De Coninck.
      Acquisition of data: Boeykens, De Coninck.
      Analysis and interpretation of data: Boeykens, De Coninck.
      Drafting of the manuscript: Boeykens.
      Critical revision of the manuscript for important intellectual content: Keller, Bosio, Wiseman, Contreras, Ventimiglia, Talso, Pietropaolo, Tailly, De Coninck.
      Statistical analysis: Boeykens, Keller, De Coninck.
      Obtaining funding: None.
      Administrative, technical, or material support: Boeykens, De Coninck.
      Supervision: De Coninck.
      Other: None.
      Financial disclosures: Vincent De Coninck certifies that all conflicts of interest, including specific financial interests and relationships and affiliations relevant to the subject matter or materials discussed in the manuscript (e.g. employment/affiliation, grants or funding, consultancies, honoraria, stock ownership or options, expert testimony, royalties, or patents filed, received, or pending), are the following: Vincent De Coninck is a speaker and/or consultant for Axess Vision Technology, BD Bard, Coloplast, and Karl Storz, but has no specific conflicts relevant to this work. Etienne X. Keller is a speaker and/or consultant for Coloplast, Olympus, Boston Scientific, Recordati, Debiopharm, and Alnylam, and has no specific conflicts of interest relevant to this work. Oliver J. Wiseman has a financial interest and/or other relationship with Coloplast, Boston Scientific, and EMS, but has no specific conflicts relevant to this work. The remaining authors have nothing to disclose.

      Appendix A. Supplementary data

      The following are the Supplementary data to this article:

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