Hello and welcome to the Stone News, a newsletter where we discuss every three months the most recent and relevant studies in stone disease.

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Dear Stone Fans. This edition takes a close look at how far endourology has come in refining precision and safety at the fibre tip. We start with an updated meta-analysis asking a deceptively simple question: does scope size still matter? The data suggest miniaturized flexible ureteroscopes hold their own against conventional calibres, reinforcing a trend toward less invasive access. 

From there, we zoom in even further — literally — with a first look at aa pre-clinical laser system that can "see" the difference between stone and soft tissue and gate its own energy accordingly, promising a new layer of built-in safety during lasering. 

Next, we turn to the often-overlooked variable of irrigation, where a bench study reminds us that flow rate can be just as critical as laser power in preventing thermal injury — and that a slowly deflating pressure bag might be a bigger risk than many of us realize. 

Finally, we step back from the operating room to look at what happens before a stone ever forms. A new study explores how urinary supersaturation influences the effectiveness of crystallization inhibitors, showing how combining thermodynamic and kinetic inhibition can enhance protection against crystal formation. It offers an interesting perspective on the mechanisms behind stone prevention and the potential value of targeting more than one step in the crystallization process.

Smaller scopes, smarter lasers, and steadier irrigation and more targeted prevention: four different angles on the same goal — safer, more controlled stone management. Let's dive in.

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This updated systematic review and meta-analysis compared small-calibre (≤6.3/7.5 F) versus large-calibre (≥7.5/9.8 F) flexible ureteroscopes by screening over 500 papers showing sparse high-quality comparative data still is in this space. 

Across the two main comparisons (6.3 vs 7.5 F, and 7.5 vs >7.5 F), there were no significant differences in stone-free rates, overall complications, or operative time, though there was a non-significant trend toward shorter operative time with smaller scopes and a signal toward more major complications with larger-calibre devices in the retrospective comparison. 

The authors conclude that miniaturized scopes achieve outcomes comparable to conventional ones, offering theoretical benefits like reduced ureteral trauma and compatibility with smaller access sheaths. The evidence remains low-to-moderate quality, with substantial clinical heterogeneity but we are seeing that miniaturization has many benefits and will be the future of endourology.

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The authors presented first pre-clinical evaluation of StoneSense™, a prototype optical module integrated into a Thulium Fiber Laser that analyzes back-reflected light to distinguish stone from soft tissue in real time, automatically gating the laser on only when the fibre is in contact with stone and shutting it off when facing tissue or when it's more than 2–4 mm away. 

In ex vivo testing on stone phantoms embedded in porcine kidney tissue, the system completely eliminated soft-tissue ablation while barely affecting stone ablation efficiency (a 3% reduction), with 100% sensitivity and 95–98% specificity depending on stone composition. 

In vivo, using five stone types implanted in the bladder, ureters, and kidneys of pigs, the system achieved complete dusting to <500 μm with no observable mucosal injury, and pooled sensitivity/specificity across all conditions was 98.5%/94.6% — though specificity dipped somewhat in the ureter with harder stones like brushite and cystine, likely reflecting both genuine detection challenges and difficulty establishing ground truth in that tight space. 

This builds on earlier autofluorescence-based recognition work for Ho:YAG but is the first such system adapted to TFL's pulse characteristics, and fits the broader trend toward optical/AI safeguards aimed at reducing unnecessary lasing and thermal injury. This is a good base for the this new techonolgy that in being used for the first time in a clinical setting at the moment.

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This study compared a standard manual pressure bag against an automated fluid management system (Asurys FMS) for thermal safety during simulated ureteroscopy. 

In a benchtop kidney model, the pressure bag's flow rate dropped 36% over 10 minutes as pressure decayed, while the FMS held a stable ~45 mL/min. That difference mattered: at 20 and 60 W, the FMS produced significantly lower calyx temperature rises than the pressure bag. 

Using a validated mathematical model extrapolated to in vivo conditions, FMS-driven flow kept calyx temperature under the 43°C injury threshold at all powers up to 60 W, whereas pressure-bag flow was predicted to breach the thermal injury threshold within about 9 minutes at 60 W — and gravity-driven flow alone could breach it at just 20 W. Limitations are notable: this is room-temperature bench data extrapolated via a simplified model using a porcine heat-transfer coefficient, lasing was into an empty calyx rather than an actual stone. 

The core takeaway is that irrigation flow rate is as important as laser power itself for thermal risk, and that manual bags have a real practical failure mode: they lose pressure and flow over time without active reinflation, often unnoticed mid-case.

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The study highlights the key role of urinary supersaturation in determining the efficacy of crystallization inhibitors, used to prevent kidney stone recurrence. This inhibitors are substances that either increase the solubility of lithogenic compounds actively reducing urine supersaturation (thermodynamic inhibition) or interfere with crystal growth (kinetic inhibition).

Using in vitro crystallization models, the study evaluated how increasing supersaturation affects several inhibitors, including citrate, hydroxycitrate, tartronate, and phytate.

The results showed that phytate was highly effective at very low concentrations, with 2 μM phytate inhibiting calcium oxalate crystal growth and aggregation more effectively than 2 mM citrate, despite the 1,000-fold higher citrate concentration. Importantly, the study also demonstrated that phytate's inhibitory effect is enhanced when combined with a compound that reduces urinary supersaturation, highlighting the potential synergy between kinetic and thermodynamic inhibition.

From a clinical perspective, this supports a dual-action approach to stone prevention, in which reducing urinary supersaturation creates a more favourable environment for crystallization inhibitors to act. This mechanism is exemplified by Lit-Control^® pH Balance, which combines magnesium, acting as a thermodynamic inhibitor, with phytate, a potent kinetic crystallization inhibitor.

The findings reinforce the scientific rationale behind Devicare's approach to kidney stone prevention and its 15-year research collaboration with the University of the Balearic Islands, focused on understanding crystallization mechanisms and developing innovative strategies for the management of urolithiasis.