STONE DISEASE

A comparison of the physical properties of four new generation flexible ureteroscopes: (de)flection, flow properties, torsion stiffness, and optical characteristics
Paffen ML, Keizer JG, de Winter GV, Arends AJ, Hendrikx AJ
Department of Urology, Catharina Hospital, and Eindhoven University of Technology, Eindhoven, The Netherlands
J Endourol. 2008; 22: 2227-34

• Background and Purpose: Several kinds of flexible ureteroscopes are in use for the removal of kidney stones. This study evaluated and compared the characteristics of four new-generation flexible ureteroscopes.
• Materials and Methods: The flexible ureteroscopes studied were: the ACMI Dur-8 Elite, the Storz Flex-X2 the Olympus XURF-P5, and the Wolf 7325.076. Measured properties included (de)flection, instrument insertion, flow properties, torsion stiffness, and optical characteristics. Active tip deflection and irrigation flow rates with and without various endoscopic tools were assessed.
• Results: All ureteroscopes score better on (de)flection with an empty working channel, compared with a channel when tools are inserted (differences minimum 0.3 degrees--maximum 80.6 degrees). The Olympus XURF-P5 is the only ureteroscope with passive (de)flection capability, whereas the ACMI DUR-8 Elite is the only ureteroscope that has a secondary active (de)flection capability. The Storz Flex-X2 and the Wolf 7325.076 ureteroscopes show nearly identical best deflection capabilities with and without tools inserted in the working channel. The longest (Olympus XURF-P5, 70 cm) and shortest (ACMI DUR-8 Elite, 64 cm) ureteroscopes have, respectively, the lowest and highest flow rates. Best optical quality is offered by the Olympus XURF-P5 and Wolf 7325.076 ureteroscopes, which have low optical distortion (-9.7; -7.7%), high resolving power (17.95; 16.00 line pairs per millimeter), and a large field of view (62.9; 63.2 degrees). The Storz Flex-X2 and Wolf 7325.076 ureteroscopes have lowest torsion stiffness.
• Conclusions: The ex vivo evaluation of the deflection capabilities, passage of instruments, flow properties, torsion stiffness, and optical characteristics yielded quantitative measures of the in vivo performance capabilities of four new-generation flexible ureteroscopes. New ureteroscopes should be subjected to this or similar evaluation and comparison. Only in this way can the urologist make an informed and objective decision regarding appropriate instrument choice.
  
  
• Editorial Comment
  In general, this is an elaborate and well-conducted study that offers helpful information in selecting the best flexible ureteroscope for clinical use. However, the study is significantly limited by the lack of statistical analysis. The authors do not report the visual acuity of the 4 observers who subjectively scored the “resolving power” of the ureteroscopes. Though the radius of curvature was qualitatively reported, no quantitative analysis was presented.
  The limiting factor in endoscopy is the quality of image. Image is everything! One can conclude based on this study that the Wolf flexible ureteroscope is optimal - low optical distortion, high resolving power and large field of view, with superior illumination compared to the Olympus scope. One limitation of this study is that only one scope was tested from each manufacturer - variance may exist between multiple scopes of the same make and model.
  Often image quality deteriorates quickly in the face of bleeding or stone fragmentation - it would be useful to evaluate the ureteroscopes under these conditions.

Dr. Manoj Monga
Professor, Department of Urology
University of Minnesota
Edina, Minnesota, USA
E-mail: endourol@yahoo.com