Does skin-to-stone distance affect the outcomes of suction mini-percutaneous nephrolithotripsy? Results from the prospective multicenter suction technology utility in mini-PCNL study (stumps)

Objectives Skin-to-stone distance (STSD) is an established predictor of shockwave lithotripsy failure, yet its influence on percutaneous nephrolithotripsy (PCNL) remains poorly characterized. This study aimed to evaluate the association between STSD and outcomes of suction mini-PCNL. Methods Prospectively collected data from 1,456 adult kidney stone patients treated with suction mini-PCNL (14–22 Fr suction access sheath) across 30 centers in 21 countries (March–November 2024) were analyzed. Patients were stratified by STSD: Group 1 (≤8 cm; n = 752) versus Group 2 (>8 cm; n = 704). The primary outcome was stone-free rate (SFR), defined as zero residual fragments on a 30-day low-dose computed tomography (CT) scan. Multivariable logistic regression identified predictors of zero residual fragments. Results Group 2 patients were older, had a higher body mass index (BMI), greater comorbidity burden (diabetes, chronic kidney disease, ASA ≥ 2), larger stone volumes, and a higher prevalence of lower pole stones. Despite this significantly different baseline characteristics, overall complication rates were comparable between groups (10.1% vs. 11.8%; p = 0.34). However, the SFR was significantly lower in Group 2 (78.2% vs. 88.7%; p < 0.001), operative times were longer (median 55 vs. 38 minutes; p < 0.001), and 72-hour readmission rates were higher (2.7% vs. 0.8%; p = 0.01). On multivariable analysis, STSD > 8 cm was an independently associated with lower odds of being stone-free (OR 0.52, 95% confidence interval (CI) 0.38–0.71; p < 0.001), alongside stone volume (OR 0.95, 95% CI 0.92–0.97; p < 0.001) and sheath size < 20 Fr (OR 0.22, 95% CI 0.12–0.37; p < 0.001). Single-step dilation (OR 2.45, 95% CI 1.65–3.64; p < 0.001) and disposable sheath (OR 1.50, 95% CI 1.09–2.05; p = 0.01) were associated with higher odds of complete clearance. Conclusions This study shows that STSD > 8 cm is independently associated with lower odds of complete stone clearance and longer operative times following suction mini-PCNL, without significantly increasing complications. Preoperative STSD measurements could inform patient counseling, surgical planning, and technical strategy selection.