The single-use digital flexible Ureteroscopy (fURS) is commonly used for the treatment of upper urinary tract stones. The size of the outer diameter of the fURS can affect the safety, efficacy, and medical costs of the treatment. Particularly for children, their ureters are thinner and more tortuous compared to adults, which places higher demands on medical devices. The investigators are interested in determining if the performance of the two different sizes of fURS (6.3 Fr vs. 8.6 Fr) are equivalent. This study will have guiding significance for the selection of upper urinary tract stones surgery in children in the future.

The single-use digital fURS is a sterile, disposable, flexible endoscope. Compared to traditional reusable digital flexible endoscopes, single-use digital fURS has lower maintenance costs, is easier to operate, and effectively avoids cross-infection between patients. With technological advancements, the size of single-use digital fURS has become increasingly slim, making them particularly suitable for children with narrow and tortuous ureters who suffered urinary stones. Currently, the single-use digital fURS used in our unit has an outer diameter of 8.6Fr. For younger children, the success rate of the first insertion of the fURS is still relatively low. When the fURS cannot pass through the ureter, it is necessary to actively dilate the ureter with a balloon in one stage, or passively dilate it with a urethral stent during the procedure to facilitate a second-stage fURS procedure. This not only increases the risk of ureteral injury but also incurs additional medical expenses. Recently, HugeMed Company has launched a single-use digital fURS with an outer diameter of 6.3 Fr, which is currently the thinnest single-use fURS in the world, and its effectiveness and safety have been preliminarily verified in clinical practice. The purpose of this study is to compare the safety and efficacy of the 6.3 Fr fURS (HU30S) and the 8.6 Fr fURS (XFGC-FU-660RC) in the clinical treatment of upper urinary tract stones in children.

Inclusion Criteria:

• Patients scheduled for ureteroscopy and laser lithotripsy for individual renal stones ranging in size from 5 mm to 20 mm in all intrarenal locations (If there are multiple stones present, the total stone burden in cross section should not exceed 20 mm)
• Patients < 14 years
• For children younger than 8 years old, the informed consent form is signed by the parents; for children older than 8 years old, the informed consent form is signed by both the parents and the child themselves.

Exclusion Criteria:

• Children with uncontrolled urinary tract infections or coagulation disorders and other contraindications for surgery before the operation.
• Children with severe renal insufficiency, anatomical or functional solitary kidney, known nephrocalcinosis, and other significant comorbidities that are not suitable for participating in the study.
• Children who refuse to participate in this study.
• Any other reason that in the opinion of the investigator would make the participant unsuitable for enrollment in the study.