【Introduction】
The treatment of complex kidney stones has long been a challenge in urology. Traditional surgeries not only require high skill from the doctors but also carry risks such as bleeding and infection. To address this issue, researchers conducted a controlled study specifically to evaluate the efficacy and safety of 3D printing technology combined with percutaneous nephrolithotomy (PCNL).

Source:Cui D, Yan F, Yi J, He D, Zhang Y, Zhang Z, Chen Y, Jiao Y, Zhang B. Efficacy and safety of 3D printing-assisted percutaneous nephrolithotomy in complex renal calculi. Sci Rep. 2022 Jan 10;12(1):417. doi: 10.1038/s41598-021-03851-2. PMID: 35013371; PMCID: PMC8748774.


【Introduction】
Kidney stones are a common disease of the urinary system. In severe cases, they can damage kidney function and affect the quality of life. Among them, complex kidney stones (such as multiple stones, horseshoe kidneys, antler-shaped stones, sponge kidneys, etc.) are particularly challenging - these stones usually have a diameter of more than 2.5 centimeters and have complex structures, making the treatment very difficult.

Currently, percutaneous nephrolithotomy (PCNL) is the main clinical treatment method for complex kidney stones. However, it also has its drawbacks: the risk of surgical complications is relatively high, and the incidence of bleeding and infection is not negligible. The rapid development of 3D printing technology has provided a new possibility to solve this problem. It can convert the digital model on the computer into a tangible and operable physical model. It has been widely applied in fields such as orthopedics and cardiac surgery for preoperative communication, planning, and training.

For simple kidney stones, traditional B-ultrasound or X-ray guidance can complete PCNL. However, for complex kidney stones, the procedure is complex, the operation time is long, and the incidence of complications is as high as 8%. Previously, some studies have attempted to use 3D printing to assist in the treatment of simple stones or single types of biconvex stones, but there are no prospective randomized controlled studies specifically targeting multiple complex kidney stones. Therefore, the researchers specifically conducted this study to verify the clinical value of 3D printing combined with PCNL.


【Materials and Methods】
This study selected patients with complex kidney stones who met the criteria. After excluding those who did not meet the standards, 90 patients were randomly divided into the 3D printing group and the control group, with 45 patients in each group (there was no significant difference in baseline data between the two groups). Based on the DICOM data from the patients' supine position thin-layer CT scans, 1:1 personalized kidney models were made using the 3D printing machine for preoperative doctor-patient communication, doctor's puncture training, and channel design. All surgeries were performed by the same doctor with 2 years of PCNL experience. Postoperative infection screening, stone clearance assessment, and follow-up were conducted; statistical analysis was performed using SPSS 23.0 software, and a P value < 0.05 was considered statistically significant.


【Results】
Patient Characteristics:

All 90 patients successfully completed the surgery. The basic conditions of the two groups were balanced and comparable: 

3D Printing Group: 25 males and 20 females, median age 45 years (ranging from 23 to 68 years), including 10 cases of bicornuate calculi, 34 cases of multiple calculi, and 1 case of horseshoe kidney. The average diameter of the calculi was 3.81 ± 1.31 centimeters. 

Control group: 29 males and 16 females, with a median age of 46 years (ranging from 24 to 67 years), including 11 cases of bicornuate calculi, 32 cases of multiple calculi, and 2 cases of horseshoe kidneys. The average diameter of the calculi was 3.60 ± 1.35 centimeters. 

There were no significant differences between the two groups in terms of gender, age, type and size of the stones (P > 0.05), which laid the foundation for the subsequent comparison of therapeutic effects.

Comparison of Surgical Conditions between the Two Groups:

All the indicators showed that the 3D printing group had a significant advantage, and the difference was statistically significant (P < 0.05): 

Doctor-patient communication: The 3D printing group scored 19.32 ± 1.57, while the control group scored 14.51 ± 2.13. The patients' understanding and satisfaction with the surgery have significantly improved. 

Surgical efficiency: The operation time of the 3D printing group was 103.21 ± 13.49 minutes, while that of the control group was 126.12 ± 25.87 minutes, with an average reduction of more than 20 minutes; the puncture time was also shorter (7.21 ± 2.32 minutes vs 9.73 ± 3.61 minutes). 

Puncture accuracy: The 3D printing group had a 97.78% match rate between the puncture target and the preoperative prediction, while the control group had a 78.78% match rate. This significantly reduced puncture errors. 

Treatment effect: The stone clearance rate in the 3D printing group was 96% (43/45), while in the control group it was 80% (36/45). There were fewer residual stones. 

Recovery speed: The hospitalization time for the 3D printing group was 6.53 ± 1.36 days, while that for the control group was 7.31 ± 1.32 days. Patients in the 3D printing group were able to recover and be discharged more quickly. 

Hemorrhage situation: The 3D printing group showed less decrease in hemoglobin (6.49 ± 4.52 g/L vs 10.33 ± 9.65 g/L) and less surgical trauma.

【Discussion】
The application of 3D printing technology in percutaneous nephrolithotomy can significantly shorten the operation time, reduce surgical bleeding, increase the stone clearance rate, lower the incidence of complications, enhance the communication effect between doctors and patients, and accelerate the patient's recovery. It is a safe and effective method for treating complex kidney stones.

With the development of materials science and engineering technology, the application of 3D printing in urology will become increasingly mature. In the future, we will continue to optimize the technology and address the current limitations, so that this technology can better serve patients with complex kidney stones.