Retrograde intrarenal surgery (RIRS) is an established minimally invasive treatment for renal stones, particularly for lower calyceal stones less than 2 cm, offering acceptable stone-free rates with low morbidity.

However, stone clearance in the lower calyx remains technically challenging due to unfavorable anatomy, limited scope deflection, and gravity-dependent fragment retention. Patient positioning during RIRS has been suggested as a modifiable factor that may influence endoscopic access, stone relocation, and surgical ergonomics.

The lithotomy position is conventionally used during RIRS, while the lateral position has been proposed to facilitate stone migration and improve lower calyceal access through gravitational assistance. Existing studies comparing patient positioning during RIRS are limited, with most evidence derived from retrospective analyses or non-randomized designs.

Therefore, this randomized controlled trial aims to compare lithotomy versus lateral positioning during RIRS for lower calyceal stones less than 2 cm in terms of operative and clinical outcomes.

Inclusion Criteria:

• Adults aged ≥18 years.
• Single or multiple lower calyceal renal stones with stone size <2 cm confirmed by NCCT.
• Negative urine culture.
• Presented cases.

Exclusion Criteria:

• Multiple stones involving renal pelvis or other calyces.
• Anatomical anomalies affecting ureteroscope access (horseshoe kidney, malrotation, ureteral strictures).
• Pregnancy.
• Prior ipsilateral renal surgery.