【Introduction】
The diagnosis and treatment of urinary system stones are becoming increasingly minimally invasive. Flexible ureteroscopy (fURS) and extracorporeal shock wave lithotripsy (ESWL) are being used more and more frequently. However, there are still a number of patients with difficult-to-treat stones who have special anatomical features and complex underlying conditions in clinical practice, and conventional minimally invasive treatments often fail. The selected literature systematically reviewed and summarized data from 28 studies involving a total of 1,014 special cases, clearly establishing the irreplaceable core position of PCNL in the treatment of four types of highly challenging stone populations.

【The four types of refractory stones are difficult to treat with conventional surgical methods】

1. Patients with urinary tract anatomical displacement

The position of the kidneys is shifted, organs are compressed, and postoperative adhesions cause the course of the ureters to be distorted. The upward passage of the flexible endoscope is blocked, making it impossible to reach the renal calyx where the stones are located.

2. Patients with neuromuscular diseases and calculi

There are abnormal bladder urination dynamics and weakened peristalsis function of the ureters. The ability to expel calculi is extremely poor. After lithotripsy, the fragments are very likely to remain and recur, and repeated conservative treatments have poor effects.

3. Patients with kidney stones after kidney transplantation

The anatomical location of the transplanted kidney and the structure of the ureteral anastomosis are special, and the spatial form is different from that of the original kidney. The difficulty of retrograde approach operation increases sharply, and the surgical risk significantly rises.

4. Patients with congenital abnormalities of the urinary system

Such as stenosis of the renal pelvis-ureter junction, duplication of kidneys, horseshoe kidneys, and abnormal kidney rotation, as well as structural disorders of the collecting system, naturally limit the operating space for flexible ureteroscopes.

Such cases are constrained by anatomical factors, and there are technical barriers in the retrograde approach. The efficiency of ESWL (Extracorporeal Shock Wave Lithotripsy) is greatly reduced, and the proportion of repeated and multiple treatments remains high.


【Complex PCNL still has existing clinical pain points】
1. Abnormal kidneys, with low structural distinctiveness of the transplanted kidneys, making it difficult to determine the three-dimensional adjacency relationships of renal calyces, blood vessels, pleura, and intestines through two-dimensional imaging;

2. The selection of the puncture point, the angle and the depth are all determined by the surgeon's experience. Any deviation in the puncture process is highly likely to cause serious complications such as massive bleeding and organ damage;

3. Physicians lack practical training materials for handling complex cases. The learning curve for mastering complex surgeries is steep and the learning process is lengthy.


【3D model enables complex PCNL】
Based on the simulation model, enhance the diagnosis and treatment capabilities for complex kidney stones in PCNL. MAXSEAS has been deeply engaged in the research and development of 3D printing models for urinary system pathologies. For complex scenarios such as transplanted kidneys, congenital kidney malformations, and anatomical ectopic stones, it provides a dual solution of preoperative planning and clinical training:
1. Individualized modeling, preoperative planning of puncture path
Extract the DICOM image data of the patients, and 1:1 physically print the complete three-dimensional models of the kidney, collecting system, stones, surrounding blood vessels and adjacent organs. This enables a clear and intuitive presentation of congenital malformations, anatomical variations of the transplanted kidney, and the overall picture of urinary tract displacement. The preoperative team can repeatedly simulate the puncture site, channel angle, and dilation depth on the physical model, select the safest puncture plan, avoid risks of vascular, pleural, and colonic damage, and transform empirical puncture into precise and quantitative planning, significantly reducing the unexpected risks during the complex PCNL procedure.

2. Customized training models to shorten the learning curve for physicians
Specialized anatomical training models for conditions such as horseshoe kidneys, duplex kidneys, transplanted kidneys, and abnormal kidney rotations have been specially created. These models are equipped with simulated stones and support the practice of puncture under ultrasound/fluoroscopy guidance, as well as the simulation of the entire process of channel dilation, stone fragmentation, and stone removal. They feature a tissue touch sensation that closely resembles that of the human body. This solution addresses the issue of limited practical operation opportunities for rare and difficult cases and the scarcity of human specimens, helping young and middle-aged physicians master the highly complex PCNL operation and enhance their ability to handle complex stone situations.

3. Intuitive visualization, enabling efficient communication between doctors and patients
The condition of complex calculi is extremely complicated and difficult for patients to understand. They have great difficulty grasping the reasons for multiple failures of minimally invasive surgeries and the necessity of PCNL (percutaneous nephrolithotomy) surgery. By using 3D physical models, the anatomical deformity characteristics, limitations of previous surgical methods, surgical principles and benefits, as well as surgical risks and expected therapeutic effects can be explained clearly. This helps to enhance patients' acceptance and treatment compliance.


【Summary】
In the current era of continuous innovation in minimally invasive techniques, ESWL and soft endoscopes have become the mainstream in the treatment of common kidney stones. However, when it comes to four types of complex stone patients - those with urinary tract displacement, neurogenic bladder, transplanted kidneys, and congenital urinary system malformations - the anatomical barriers are insurmountable. PCNL remains the most stable core treatment method for achieving complete cure.

The core bottleneck of complex PCNL lies in precise puncture and preoperative prediction. MAXSEAS uses high-precision 3D printing of pathological models to connect the two major aspects of preoperative planning for difficult cases and specialized standardized training, helping urology departments overcome challenging complex kidney stones more safely and efficiently, and fully leveraging the irreplaceable clinical value of PCNL.