Residual renal stone fragments remain a common clinical issue following percutaneous nephrolithotomy (PCNL), with reported incidence ranging from 10% to 30%. These fragments may act as a nidus for recurrent stone formation, infection, or obstruction, necessitating further intervention. Extracorporeal shock wave lithotripsy (ESWL) is widely used as a non-invasive treatment option for such residual stones; however, the optimal timing of ESWL after PCNL remains unclear.

Early application of ESWL may enhance stone clearance before fragment embedding or encrustation occurs, but it could be associated with increased risk of bleeding or infection due to incomplete renal healing. Conversely, delayed ESWL allows for better tissue recovery but may permit stone growth or persistence of symptoms.

This prospective randomized comparative study aims to evaluate the optimal timing of ESWL after PCNL in patients with residual renal stones ≤15 mm. Eligible patients will be randomized into two groups: early ESWL (within 7-14 days after PCNL) and delayed ESWL (after 3-4 weeks). The primary outcome is the stone-free rate at 3 months, while secondary outcomes include complication rates, pain scores, renal function changes, and the need for additional interventions.

The results of this study are expected to provide evidence-based guidance on the ideal timing of ESWL following PCNL to maximize efficacy and minimize complications.

Percutaneous nephrolithotomy (PCNL) is considered the gold standard treatment for large and complex renal stones. Despite advances in surgical techniques and imaging, residual stone fragments (RFs) remain a relatively common finding after PCNL, with reported rates ranging from 10% to 30%. These residual fragments are clinically significant, as they may serve as a nidus for recurrent stone formation, urinary tract infection, obstruction, and the need for secondary interventions.

Extracorporeal shock wave lithotripsy (ESWL) is a widely accepted, non-invasive modality for the management of residual renal stones following PCNL. However, the optimal timing for performing ESWL after PCNL remains controversial. Early ESWL may improve stone clearance rates by targeting fragments before they become embedded within the collecting system or undergo encrustation. On the other hand, early intervention may be associated with an increased risk of complications, such as bleeding or infection, due to incomplete renal parenchymal healing after PCNL.

Delayed ESWL allows for adequate healing of renal tissue, potentially reducing procedure-related complications. However, postponing treatment may allow residual fragments to increase in size, migrate, or become symptomatic, which could negatively impact overall outcomes and increase the likelihood of additional interventions.

Given this clinical uncertainty, this study is designed as a prospective, randomized, comparative clinical trial to evaluate the optimal timing of ESWL after PCNL. Patients who undergo PCNL and are found to have residual renal stones measuring ≤15 mm on postoperative imaging (non-contrast CT or ultrasound) will be considered eligible for inclusion.

Eligible participants will be randomly assigned in a 1:1 ratio into two groups:

Group A (Early ESWL): Patients will undergo ESWL within 7-14 days after PCNL. Group B (Delayed ESWL): Patients will undergo ESWL after 3-4 weeks following PCNL.

All patients will be treated using the same lithotripter system, with standardized ESWL parameters (energy level, frequency, and number of shocks) according to current European Association of Urology (EAU) guidelines. A maximum of three ESWL sessions will be allowed per patient, with appropriate analgesia or sedation provided as needed.

Patients will be followed up clinically and radiologically. Imaging (ultrasound or non-contrast CT) will be performed after completion of ESWL sessions to assess stone clearance. Stone-free status will be defined as the absence of residual fragments greater than 2 mm. Final assessment of the primary outcome will be conducted at 3 months.

The primary outcome measure of the study is the stone-free rate (SFR) at 3 months.

Secondary outcome measures include:

Procedure-related complications (e.g., hematuria, fever, urinary tract infection, steinstrasse) Post-procedural pain assessed using the visual analog scale (VAS) Changes in renal function (serum creatinine) Need for auxiliary procedures such as ureteroscopy (URS) or repeat PCNL Statistical analysis will be performed using SPSS software. Continuous variables will be expressed as mean ± standard deviation and compared using Student's t-test. Categorical variables will be expressed as percentages and compared using the Chi-square test. A p-value < 0.05 will be considered statistically significant. Analysis will be conducted on an intention-to-treat basis.

This study aims to provide high-quality evidence regarding the optimal timing of ESWL after PCNL, which may help improve clinical outcomes, reduce complications, and guide future urological practice guidelines.

Inclusion Criteria:

• Age 18-70 years.
• Single or multiple residual renal stones ≤15 mm after PCNL.
• Normal renal function (serum creatinine <1.5 mg/dL).
• No active UTI.

Exclusion Criteria:

• Bleeding disorders or anticoagulant therapy.
• Obstructed drainage or active sepsis.
• Stones >15 mm or requiring secondary PCNL.