Innovation, development and clinical adoption of ureteroscopy: a time trend since its first inception

Abstract

Flexible ureteroscopes embody the combination of many inventions. Initially suitable only for diagnostic purposes, currently retrograde intrarenal surgery (RIRS) is the primary option of renal stones up to 2 cm [1]. It is surprising that this journey started 70 years ago, and each subsequent decade is characterised by a rapid acceleration in the development of flexible ureteroscope architecture (Fig.1). In 1954, Harold H. Hopkins described the basic ideas behind optical glass fibre [2]. The first results of using fibre optic ureteroscopes dates back to the 1960s [3, 4]. However, they lacked a tip-deflection mechanism and an internal working channel, limiting their use for diagnostics in general. In the 1980s, the optimal fibre optic light bundles with tip-deflection mechanisms were developed along with and the first prototypes with the presence of a working channel [5]. By the late 1980s, the generally accepted specifications for flexible ureteroscopes were 10 F outer diameter, unidirectional active tip deflection, and 3.6 F working channel size. Interestingly, today's ureteroscopes still primarily use the latter specification [6]. Up until 2006, subsequent efforts focused on improving these characteristics, specifically on miniaturising them and increasing the maximum up/down deflection degree. So, by this time, Semiflex Scope™ (Maxiflex®, New Orleans, LA, USA) with the smallest diameter of tip and overall shaft (6.3 F) and Flexvision U500™ (Stryker®, Kalamazoo, MI, USA) with extended bidirectional deflection of 275° had been developed. Additionally, the Flex-X2™ from Karl Storz® (Tuttlingen, Germany) has achieved an increase in field of view up to 110°, with oval distal tip. In 2006, Gyrus ACMI® (Westborough, MA, USA) released the first digital ureteroscope that was based on a complementary metal-oxide semiconductor (CMOS) chip and light-emitting diode (LED; Invisio DUR-D™), and the following year, an appropriate standard for high-definition medical imaging was established (Medical-HD). In addition, in the period 2007–2009, the first digital ureteroscopes based on a charge-coupled device (CCD) chip (URF-V™, Olympus®, Tokyo, Japan) appeared. Between 2007 and 2009, Richard Wolf® (Knittlingen, Germany) released the ureteroscope with a 6-F distal tip (Viper™), continuing the general trend towards the miniaturisation of instruments. Additionally, the same manufacturer introduced Cobra™, the first and only fibre optic flexible ureteroscope with two working channels (3.3 F and 3.3 F), designed to actively crush and remove stones without disrupting the irrigation flow. Richard Wolf® is the only manufacturer to integrate multiple working channels, as evidenced by its models. The key stage of the miniaturisation trend was in 2017, when Olympus® introduced the ureteroscope with the slimmest tip among all previously and currently known instruments, the URF-P7™ (4.5 F). A further revolution was the first disposable digital ureteroscope (LithoVue™) from manufacturer Boston Scientific® (Marlborough, MA, USA) in 2016 [6]. Thus in 2017, Neoscope™ with the largest bidirectional deflection (280°/280°) among single-use endoscopes was released, and Riwo D-URS™ by Richard Wolf® with such capabilities up to 300° was released in 2022–2023, and Lscope URS3006™ (Seplou®, Loganville, GA, USA) with the slimmest tip (6.6 F) was released in 2019–2021. The distal end diameter of digital and fibre optic ureteroscopes differs significantly by 2 F, primarily due to the former's ‘chip-on-tip’ design [6]. This design directly influences the distal end diameter. On the other hand, image quality is significantly higher when using digital ureteroscopes. Thus, in 2017–2018, Dornier® (Munich, Germany) introduced the AXIS™ endoscope with the largest field of view (120°) among all flexible ureteroscopes, regardless of technological basics. Parallel to the advancements in flexible ureteroscopes, several issues have emerged, including the susceptibility of the optics a