We retrospectively evaluated patients with unilateral complex kidney stones who underwent PCNL between January and December 2022. This study was approved by the ethics committee of Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, and the observational study were followed by the STROBE guidelines. Patients with complex kidney stones (based on specificities defining a complex kidney stone: stone size, stone density, stone location or anatomical abnormalities) were selected, and the inclusion and exclusion criteria were as follows.

(1) Age between 20 and 70 years.

(2) The patients were diagnosed with unilateral complex kidney stones by kidney, ureter, and bladder (KUB) X-ray, and non-contrast computed tomography (NCCT), which showed clinical features of multiple calyces and multiple stones with a total stone burden of more than 25 mm.

(3) S.T.O.N.E. scores were all 9 and above (where N score was 2 or more, i.e. multiple calyceal involvement or staghorn calculi).

(4) The patients can tolerate percutaneous nephrolithotripsy and completed surgery.

(5) Follow up with postoperative review can be completed.

(1) Patients with bilateral kidney stones.

(2) Isolated kidney or renal insufficiency (serum creatinine > 177 µmol/L);

(3) Renal malrotation, horseshoe kidney, or abnormal intrarenal anatomy.

(4) Excessive adiposity, body mass index (BMI) ≥ 35.

(5) Severe scoliosis or left kidney stone with splenomegaly.

(6) Uncorrected coagulation disorder.

(7) Uncorrected severe cardiopulmonary dysfunction.

(8) Urinary tract infections that are not effectively treated.

All patients were examined with KUB X-ray and NCCT of the urinary system before treatment to understand the stone size, location, degree of hydronephrosis, and exclude renal malformations. Urine routine and urine culture were performed to assess urinary infection. Biochemical routine examination was performed to evaluate renal function. Complete blood routine, coagulation function, electrocardiogram and other examinations to exclude surgical contraindications. Antibiotics were administered prophylactically 30–60 min before surgery.

Following the successful administration of general anesthesia, the patient was positioned in the prone position after the ureteral catheter was inserted. In combined with the preoperative imaging data, the renal cortex and medulla, upper and lower pole of the kidney, stones, hydronephrotic calyces and perinephric viscera were examined by ultrasound. To establish the percutaneous nephroscopy working channel using a visual needle nephroscope (“Needle-perc”, Youcare@, Wuhan, China, Fig. 1), we tried to select the middle and upper calyces of the postrenal group, and we performed a vertical puncture of the highest point of the dome of the target calyces through 11 intercostal or 12 subcostal under ultrasound real-time guidance. Nephrostomy tract dilatation was completed by peel-away sheath of 20 F and the nephroscope was entered into the percutaneous renal channel. The stone was fragmented with the power set at 30–60 W (2.0–3.0 J / 15–20 Hz) by a 550 μm holmium laser fiber, Throughout the procedure, we employed continuous irrigation and real-time monitoring of both laser power and tissue temperature to ensure patient safety and minimize the risk of thermal injury during the lithotripsy. After treating most of the main body of the stone by percutaneous nephroscopy, the residue of the calyceal stone was examined by B-ultrasound, and precision puncture was performed by using the “Needle-perc” to locate the calyces where the residual stone was located, as a secondary channel, without dilation of the channel. A 200 μm holmium laser fiber, with the power set at 12–20 W (0.8–1.0 J / 15–20 Hz) was used to deal with residual stones, in which larger stone fragments can be moved to the vicinity of main 20 Fr channel with the help of endoscopy and fluid and removed from it. A 6 F ureteral stent tube, main access nephrostomy tube, and balloon urinary catheter were routinely retained after surgery.

Structural diagram of the visualization needle nephroscope (“Needle-perc”). The length of the nephroscope body is 152 mm and the outer diameter is only 4.2 F, which is almost equivalent to that of a common puncture needle, and it has a perfusion channel, an endoscope channel and a working channel

All patients had the urinary catheter and nephrostomy tube removed 3–4 days after surgery and the ureteral stent tube removed 2–3 weeks after surgery. The postoperative antibiotic was given for 24–48 h. All patients underwent postoperative KUB X-ray and NCCT to assess whether there were any residual stones 2–3 days after surgery. While KUB X-ray serves as a standard initial assessment tool due to its accessibility and speed presented in Fig. 2, we recognize that NCCT is the gold standard for accurately detecting residual stones, given its superior sensitivity and specificity.

Comparison of preoperative and postoperative KUB imaging results of a typical case treated by standard PCNL combined with visual needle nephroscope. (a) The red arrow shows the kidney stones before surgery. (b) Postoperative KUB 2 days after surgery

A review at 30 days to assess stone clearance as a follow-up was received by the patients. To ensure a comprehensive evaluation of the stone-free rate (SFR), we interpreted the results from both imaging modalities. KUB X-ray results were used for preliminary assessment, while NCCT findings were prioritized for confirmation of any residual stone burden. Clinically significant residual stones were identified with a diameter of ≥ 4 mm. The operation time, the proportion of complications, the stone-free rate of one-stage operation were recorded (presented in Fig. 3). Complications were classified according to the Clavien grading system [5]. Data were reported as numbers, percentages, and mean ± standard deviation (SD).

Establishment the main working channel by “Needle-perc” under ultrasound real-time guidance