This study centers on the treatment of low pole renal stones by flexible ureteroscope and intends to find the key anatomical parameters using a prospective, randomized multi-center trial design and to make a more appropriate standard for flexible ureteroscopy of low pole renal stones.

With the development of manufacturing technique, new generation of flexible ureteroscopes have great initiative and passive bending capacity and have greatly expanded its application. In our clinical practice, we have found that IPA (Infundibulopelvic angle) is no longer a decisive factor for the success of f-URS（flexible ureteroscope） surgeries. Thus, we think it is necessary to have further study on the effect of anatomy of renal collecting system for f-URS surgeries.

Inclusion Criteria:

• • Subject has provided informed consent and indicated a willingness to comply with study treatments

  • Subject is 18-70 yrs of age
  • Subject can be either male or female
  • Subject has a diagnosis of low pole renal stones according to CT urography(CTU) or intravenous pyelogram (IVP) results
  • Subject has a single stone 1~2cm in size (KUB), or multiple stones 1~2cm in cumulative size (KUB), and is a surgical candidate for the ureteroscopic approach

Exclusion Criteria:

• • Subject has an active urinary tract infection (e.g., cystitis, prostatitis, urethritis, etc.)

  • Subject has been diagnosed with a urethral stricture or bladder neck contracture
  • Subject has been diagnosed with a urinary tract infection related to stone obstruction within two weeks
  • Subject has severe hematuria that might blur the vision of the endoscopy
  • Subject is pregnant or in monthly period
  • Subject has coexistent disease like systemic disease, heart disease, lung disfunction or other diseases that could not tolerate the endoscopic surgery or anesthesia.
  • Subject has unadjusted diabetes or high blood pressure
  • Subject has a disorder of the coagulation cascade system that would put the subject at risk for intraoperative or postoperative bleeding
  • Subject is unable to discontinue anticoagulant and antiplatelet therapy preoperatively (2 weeks)
  • Subject has been diagnosed with hydronephrosis larger than 3cm according to the B-scan ultrasonography examination
  • Subject has any kind of anatomic abnormality of the urinary system that might have an influence on the surgery

low pole renal calculus patients