Knowledge-map analysis of percutaneous nephrolithotomy (PNL) for urolithiasis

Urolithiasis is a common urological disorder, which includes kidney stones, ureteral stones, bladder stones, and urinary tract stones. The incidence of urolithiasis ranges from 7–13% in North America, 5–9% in Europe, and 1–9% in Asia [1]. The main symptoms of urolithiasis are sudden onset of low back pain and hematuria. Urolithiasis may lead to serious consequences without timely treatment, such as hydronephrosis, uremia, infection and abscess, acute kidney injury, and renal failure, threatening patients’ health and life [2‐9]. However, it is reported that the prevalence and incidence of urolithiasis are increasing worldwide, which is threatening human’s civilization and health [10, 11].

There are three treatments for urolithiasis: extracorporeal shock wave lithotripsy (ESWL), ureteroscopy, and percutaneous nephrolithotomy (PNL) [12]. Among them, PNL shows the highest stone clearance rate in the surgical treatment of urolithiasis according to the American Urological Association guidelines. In contrast, ESWL is the least efficient [13, 14]. For this reason, PNL is widely studied and used on the treatment of urolithiasis. Despite the high efficiency of PNL, there is no bibliometric analysis of the publication trend of PNL in the treatment of urolithiasis through visual analysis.

Bibliometrics is a statistical method for quantitative analysis of research papers related to a topic through mathematical methods [15‐17]. Bibliometrics can evaluate the quality of research, find the most valuable topics in the field, and identify research hotspots. Bibliometric analysis can also find the relationship between studies, predict the future research directions, provide new ideas for researchers, and greatly improve the efficiency of scientific research. The Web of science (WOS) online database provides the data for bibliometric analysis, and the data will be imported into softwares such as VOSviewer for further analysis.

The purpose of this study was to use bibliometric method to analyze a large number of studies on PNL in the treatment of urolithiasis from a macro perspective. By understanding the characteristics of bibliometrics analysis, we provided research directions and specific tasks that may belong to related research fields.

In this study, we analyzed 3103 publications about PNL and urolithiasis indexed in WOS core database. Through a co-analysis of publication outputs, we knew that research on PNL was maturing. We found that the number of publications was almost the same each year, and there were no major fluctuations, which meant that studies on PNL were growing at a steady rate. Most of these publications were written in English, probably because English-speaking countries dominated this field. In the keywords analysis, the results showed that the most frequent keywords were the applications of PNL, the treatments of urolithiasis, and the complications of PNL, which met our expectations.

Based on publications and citation analysis, we got the top 10 most-cited articles. At the top of the list were two important guidelines [12, 18]. Moreover, 5 of the top 10 articles were about the complications of PNL. PNL can cause bleeding, urine extravasation, and fever, while damage to the colon or pleura was rare [19, 20]. Hemorrhage was one of the most important complications of PNL. Surgical complications (P < 0.0001), mature nephrostomy (P < 0.0001), operative time (P < 0.0001), approach guidance method (fluoroscopy vs ultrasound) (P = 0.0001), expansion method (P = 0.0001), multiple (> or = 2) bundles (P = 0.003), bundle size (P = 0.001), renal solid thickness (P = 0.05), and diabetes mellitus (P = 0.05) were important factors to predict blood loss [21, 22]. Christian Seitz et al. [23] discussed the incidence, prevention, and management of postoperative complications of PNL in more details. A categorization method (Clavien score) for the evaluation of postoperative complications of PNL was established and validated, with high validity for the complications on duration of stay but low reliability for the evaluation of minor complications [24, 25]. A large number of studies on complications proved that PNL was mature and in the stage of self-optimization and improvement. It was worth noting that one of the top 10 articles discussed the relationship between PNL, urolithiasis, and socioeconomic burden. Although the research had a long history and had little reference value for the present, it can still reflect the positive impact of PNL on the social economy in the process of development [26]. Further study of postoperative complications of PNL showed that PNL was widely used and mature. The journals that published the most articles on this topic were Journal of Urology, European Urology, and Journal of Endourology. Among the top 20 journals that published articles of this field, publications accounted for more than half of the total, which may indicate that articles in the field were published intensively.

From the perspective of country analysis, the United States was the most developed country in this field, with the largest number of articles and the highest H-index, indicating that the United States led not only in quantity but also in quality in this field. Therefore, it is urgent to improve the research quality of Chinese scholars. Although there were also a large number of articles published in China, its H-index was relatively low, which may indicate that Chinese scholars value quantity more than quality. Moreover, it is worth noting that although the total number of papers published in India was relatively small, its H-index was high, indicating that the research quality of Indian scholars was relatively high.

From the author’s analysis, we can also see that the one who published the most articles was a Chinese scholar with a relatively low H-index. A Turkish scholar with the highest H-index published less than half of that Chinese scholars, which further confirmed that Chinese scholars paid more attention to the quantity of research rather than the quality. In terms of cooperation between countries, the United States had close cooperation with Canada, China, Italy, and many other countries, because higher research quality brings the United States closer to international cooperation.

In conclusion, this study not only provided urologist with valuable information about PNL and urolithiasis, but also provided a new way for researchers to understand urolithiasis. This manuscript also helped investigators understand research hotspots, collaborating institutions, and research frontiers.