Retrograde intrarenal surgery (RIRS) is a minimally invasive treatment for renal stones, yet stone-free rates (SFR) vary based on patient and stone characteristics. This study aims to evaluate predictive factors, including infundibular pelvic angle (IPA), stone parameters, and operative factors, influencing SFR after RIRS. Ureteric stones and primary pyeloscopy procedures were excluded.

A retrospective analysis was conducted on 46 patients who underwent RIRS for lower pole stones (excluding ureteric stones and primary pyeloscopy procedures). Patient demographics (age, sex, BMI), stone parameters (size, number, Hounsfield units), operative details (laser settings, operative time), and IPA (measured on preoperative CT) were analyzed. SFR was defined as absence of fragments >2 mm on follow-up imaging. Statistical analysis identified predictors of SFR.

Mean patient age was 49.2 ± 11.8 years (58% male, mean BMI 26.8 ± 3.9 kg/m²). Mean stone size was 13.7 ± 4.6 mm, with 28% exhibiting multiple stones. Mean IPA was 42.3° ± 10.8°. Overall SFR was 73.9%. Multivariate analysis identified smaller stone size (<10 mm, p=0.008), IPA >40° (p=0.02), and single-stone burden (p=0.04) as independent predictors of SFR. Operative time and laser type showed no significant correlation.

This study found a 73.9% stone-free success rate, with three key predictors: stones <10mm had better outcomes (p=0.008), a favourable infundibular pelvic angle >40° doubled success (p=0.02), and single stones performed better than multiples (p=0.04). Surprisingly, operative time and laser type didn't affect results. The findings suggest preoperative CT should include IPA measurement, as stones in steep anatomies (IPA<40°) may need alternative treatments. While confirming known size limitations, this highlights how anatomical factors significantly impact RIRS success for challenging lower pole stones. The results help guide patient selection but require validation in larger studies.

For lower pole stones treated with RIRS, stone size, IPA >40°, and solitary stones significantly improve SFR. IPA measurement may enhance preoperative patient selection. Larger prospective studies are needed to validate these findings.