Urinary calculus is a globally recognized urological condition, with prevalence rates ranging from 1% to 13% across different geographical regions (1) Therapeutic approaches for renal calculi encompass extracorporeal shock wave lithotripsy (ESWL) and minimally invasive endoscopic surgical techniques, such as percutaneous nephrolithotomy (PCNL) and retrograde intrarenal surgery (RIRS). Treatment plans depend on the characteristics of calculi, patient factors, surgeon experience and the condition of medical centers. According to the guidelines of American Urologic Association (AUA) and European Association of Urology (EAU), patients with a burden of less than 20 mm in kidney calculi can choose RIRS as the frst-line surgical treatment with good stone-free rate (SFR). (2, 3) The application of RIRS for urinary stones has increased signifcantly, and the indications have expanded due to developments in minimally invasive technology and equipment. (4) With the development of stone retrieval devices and miniaturized fexible ureteroscopes, RIRS is more widely used for treating renal calculi, even for high burden stones. (5, 6) The application of ureteral access sheath (UAS) in RIRS can improve surgical vision, reduce intrarenal pressure (IRP), and decrease postoperative infectious complications. (7-9) Several reports have demonstrated the superiority of suctioning UAS, including shorter operation time, higher SFR and lower incidence of infectious complications compared with traditional ureteral access sheath, but none of these suctioning UAS can reach the renal calyces. (10-12)

A novel tip-flexible suctioning ureteral access sheath with flexible terminal was designed, which delivered the tip of the ureteral access sheath to renal calyces. However, data comparing novel tip-flexible suctioning ureteral access and traditional ureteral access sheath is lacking in RIRS.

Therefore, we designed a prospective controlled analysis to compare the efficacy and safety of novel tip-flexible suctioning ureteral access sheath and traditional ureteral access sheath combined with flexible ureteroscope (FURS) in treating renal calculi.

Inclusion Criteria:

• Diagnosis: Radiologically confirmed renal stones (e.g., CT, ultrasound, or X-ray).
• Stone size within a specific range (e.g., 5-20 mm).
• Indication for Treatment: patients indicated for flexible ureteroscopy due to renal stones.
• Anatomical Suitability: normal or mildly altered renal anatomy that allows safe use of the access sheath.
• Willingness to participate and provide written informed consent.

Exclusion Criteria:

• - Medical Conditions: Active urinary tract infection (UTI) or sepsis. Coagulopathy or inability to discontinue anticoagulation therapy. Significant comorbidities (e.g., severe cardiopulmonary disease). Pregnancy: Pregnant or breastfeeding individuals.
• Anatomical or Surgical Factors:

Severe ureteral stricture or obstruction preventing sheath placement. Congenital abnormalities affecting the urinary tract. - Stone Factors: Stones larger than the sheath's operational limit (e.g., >20 mm). Multiple stones in different calyces that cannot be accessed in one session.

- Previous Treatment: Recent (<6 weeks) or repeated interventions for the same stones (e.g., prior lithotripsy or ureteroscopy).