Fragmentation Vs Dusting With FANS for Renal Stones Less Than 2cm: A Randomized Controlled Study

Urolithiasis is among the most prevalent urological disorders worldwide, with a lifetime recurrence risk ranging from 30 to 50% in affected individuals. Global Burden of Disease study in 2021 estimated 106 million new incident cases of urolithiasis globally, representing a 47% increase from 1990, driven by population growth, changing dietary patterns, rising rates of metabolic syndrome, and climate-related factors. Regions with tropical and subtropical climates including South Asia bear a disproportionately higher burden, with prevalence estimates of 5-10% compared to 1-5% in temperate regions. Nephrolithiasis is not merely a surgical inconvenience; it imposes significant morbidity through recurrent renal colic, obstructive uropathy, urinary tract infection, and progressive renal dysfunction, with substantial associated healthcare costs.

Retrograde Intra-Renal Surgery (RIRS) has become the preferred minimally invasive modality for the definitive management of most renal calculi endorsed by both the European Association of Urology (EAU) and the American Urological Association (AUA) for stones amenable to endoscopic treatment. It offers the advantage of direct pyelocaliceal access without the morbidity of percutaneous access, with established stone-free rates (SFR) exceeding 90% for stones less than 2 cm in contemporary series.

The operative strategy employed during RIRS specifically, the choice between stone fragmentation and stone dusting remains a subject of active clinical debate, with meaningful implications for operative efficiency, stone-free outcomes, and scope longevity. Fragmentation involves delivering high pulse energy (typically 0.8-1.5 J) at low frequency (5-10 Hz) to reduce calculi into retrievable fragments of less than 4 mm. Dusting employs low pulse energy (0.2-0.5 J) at higher frequency (15-25 Hz) to ablate the stone into sub-millimetre powder particles. In the holmium:YAG (Ho:YAG) laser studies, fragmentation consistently demonstrated superior SFRs. El-Nahas et al. reported a significantly higher SFR with fragmentation compared to dusting (78.6% vs. 58.6%, p=0.035) at 2 months on non-contrast CT, albeit at the cost of a longer operative time (91 vs. 76 minutes, p=0.009). A 2023 systematic review and meta-analysis corroborated these findings, demonstrating that dusting was associated with a lower pooled stone-free rate (OR 0.60; 95% CI 0.41-0.89, p=0.01) and a significantly higher re-treatment rate (OR 2.03; 95% CI 1.31-3.13, p=0.001), though with a shorter operative time and comparable complication profile. These data, however, were generated predominantly with Ho:YAG laser technology and without active suction-assisted clearance, a critical limitation in extrapolating these findings to contemporary practice.

The Thulium Fiber Laser (TFL), introduced into clinical practice in 2018, represents a fundamental technological shift from the Ho:YAG platform. Operating at a wavelength of 1,940 nm, TFL demonstrates a four- to fivefold higher water absorption coefficient, a lower stone ablation threshold, and a more uniform rectangular pulse profile compared to the asymmetrical spike-decay waveform of Ho:YAG. These physical characteristics translate to superior ablation efficiency. TFL achieves fragmentation speeds up to twice and dusting speeds up to ten times faster than Ho:YAG at comparable settings, with significantly less stone retropulsion. Crucially, unlike Ho:YAG where increasing pulse energy generates larger residual fragments, TFL dusting at higher pulse energies does not increase fragment size producing dust particles consistently below 0.254 mm regardless of energy setting, making it inherently better suited to achieving fine, clearable particulate. A systematic review and meta-analysis of TFL-based RIRS reported a pooled SFR of 89.37% (95% CI: 83.93-93.12%), with TFL use independently associated with higher odds of achieving zero-fragment status in multivariable analysis.

The introduction of FANS has fundamentally altered the operative landscape of RIRS by enabling continuous active suction-assisted clearance of ablated stone material in real time. In conventional RIRS without active suction, the inferior stone-free rates historically associated with dusting were largely attributable to inadequate clearance of residual particulate from the pelvicalyceal system. With use of FANS, this limitation is addressed with fragments produced by fragmentation and dust produced by dusting both evacuated under the same negative-pressure suction system. Fragmentation with FANS requires high-energy to reduce stone burden into small fragments, followed by active suction of residual fine material. Dusting with FANS, on the other hand, converts the entire stone volume into sub-millimetre particulate that is continuously suctioned away during lasing potentially offering a more streamlined workflow with potentially less energy usage, reduced mechanical stress on the ureteroscope working channel, and fewer scope withdrawals. Given TFL's inherent superiority in generating fine, consistently small dust particles irrespective of pulse energy; the combination of TFL dusting with FANS-assisted real-time evacuation may produce stone-free outcomes equivalent or superior to fragmentation, while offering these additional operative efficiencies.

Whether dusting using TFL with FANS is non-inferior or indeed superior to fragmentation using TFL with FANS in terms of stone-free rate at one month has not been evaluated in any prospective randomised trial. This study is designed to answer that specific question in patients with renal stone less than 2cm, using a rigorously standardised equipment framework, blinded NCCT KUB-based outcome assessment, and a pre-specified non-inferiority margin of 10%.

Inclusion criteria

• Age ≥18 years
• Renal stone(s) confirmed on non-contrast CT KUB
• Total stone less than 2cm
• Stone amenable to flexible ureterorenoscopy (FURS)
• FANS advanced beyond Pelvi-Ureteric Junction (PUJ)
• Able and willing to provide written informed consent
• Able to comply with follow-up schedule

Exclusion criteria

• Active urinary tract infection (positive urine culture) at time of planned surgery
• Anatomical anomalies precluding safe FURS (e.g., infundibular stenosis, severe calyceal diverticulum inaccessible to flexible scope)
• Pregnancy or breastfeeding
• Prior ipsilateral renal surgery within 3 months of enrollment
• Concurrent ureteral stone(s) requiring simultaneous treatment
• Renal anomalies: horseshoe kidney, ectopic kidney
• Sheathless procedure
• Unable to comply with follow-up or provide consent
• Participation in another interventional trial within 30 days