Ultrasonic propulsion clears residual stone fragments in kidney

More patients who underwent ultrasonic propulsion (UP), facilitated by an independent group of operators, benefit from the passage of residual kidney stone fragments and from a decreased stone burden than those who did not receive treatment, a recent trial has shown.

“The increase in stone fragment passage rate with the UP procedure was comparable with an index study that also showed the long-term benefit of reduced occurrence of future stone events,” the investigators said.

The trial was conducted from April to October 2024 and included 24 participants (treatment group: n=12; control group: n=12). Stone fragments persisted for a median of 6 months following surgery prior to study enrolment. [J Urol 2025;214:3-9]

Ten of the 12 participants who underwent UP passed fragments as opposed to just two in the control group (p=0.003). Nine patients in the treatment group also showed a reduction in stone burden on imaging relative to one of 11 controls (p=0.003).

In terms of safety, adverse events (AEs) occurred in seven of 12 treated participants and four of 14 controls. All AEs were mild in severity.

“Consistent with the index study, UP conducted by an independent group of operators demonstrated a higher rate of fragment passage and greater reduction in stone burden after UP compared with controls, with minor associated risk,” the investigators said. [J Urol 2024;212:811-820]

“These results contributed to Food and Drug Administration clearance of the first UP device, and with trials by others, lay the groundwork for broad clinical use,” they noted.

Limitations

This multicentre, prospective, open-label, randomized, controlled trial involved adults with residual fragments ≤5 mm seen on clinical imaging at least 4 weeks after lithotripsy. Twelve patients received UP, while another group of 12 participants did not.

Efficacy endpoints included the proportion of participants reporting visual observation of stone passage within 3 weeks postprocedure (treatment group) or -randomization (controls) and the reduction in stone burden on follow-up imaging captured within 90 days following the procedure or randomization.

Safety endpoints were AEs within 3 weeks after the procedure or randomization. The investigators used the Fisher exact test for comparison.

The study, however, was relatively small, with few non-White participants, which attenuates generalization of the results. In addition, the urologists and participants were not blinded.

“However, fragments were photographed in all treatment cases, and follow-up imaging demonstrated a greater decrease in overall stone burden in the treatment group, confirming the reported stone passage results,” the investigators said.

Ultrasound technology

UP belongs to a new generation of ultrasound-based modalities for stone treatment, which include burst wave lithotripsy (BWL), in awake patients.

BWL treats fragment stones and is safe and effective for stones up to 12 mm in size. On the other hand, UP repositions small stone fragments to allow their passage. The ultrasound pulses in BWL are shorter in duration and have a higher amplitude compared with UP. [J Urol 2022;208:1075-1082; J Urol 2022;207:1067-1076; J Urol 2024;212:580-589]

“Both technologies can be performed with the same machine and are synergistic,” according to the investigators. [J Urol 2025;214:41-47]