The impact of clinically insignificant residual fragments following endourological management of urolithiasis: a systematic review of complications and re-intervention rates.

Introduction: Achieving stone-free status (SFS) is a key goal of endourological treatment, yet definitions of SFS and clinically insignificant residual fragments (CIRF) remain controversial. While CIRF is frequently defined as residual fragments ≤4 mm, there is no consensus on its clinical significance regarding complications and re-intervention needs. We evaluate the risk of complications and the need for re-intervention associated with the presence of CIRF following endourological treatment for urolithiasis.

Evidence acquisition: PubMed/Medline, Scopus, Web Of Science, and Embase databases were searched for articles relating to SFS and CIRF definitions and outcomes, in February 2025, using keyword combinations: "stone-free rate," "residual fragments," "clinically insignificant residual fragments," "urinary calculi," "urolithiasis," "complications," and "outcome". Inclusion criteria were all studies with SFS/CIRF definition and complications associated with residual fragments following treatment (shock wave lithotripsy, ureteroscopy, or percutaneous nephrolithotomy).

Evidence synthesis: Fifty-two studies met inclusion criteria. From the pooled analysis the probability of spontaneous expulsion of CIRF≤4 mm was 33% (95% CI: 12-50%; P<0.001), while regrowth occurred in 32% (95% CI: 23-40%; P<0.001). CIRF-related complications were observed in 27% (95% CI: 21-34%; P<0.001), and the re-intervention rate was 21% (95% CI: 16-26%; P<0.001). Within a variable mean follow-up ranging from 3 to 59 months. The risk of bias was moderate overall, with single-arm studies exhibiting the highest bias risk.

Conclusions: Patients with CIRF≤4 mm should be monitored closely and informed about the non-neglectable likelihood of complications and of re-intervention. On the other hand, they have one probability out of three of spontaneous passage. Endourologist and patients should be aware of these outcomes to better plan the management, follow-up, and the "insignificant" nature of residual fragments. Hence, the aim of surgeries should be achieving the complete SFS, especially in high-risk stone former patients.