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A novel method to measure the mechanical pushing and pulling forces during ureteroscopy in a normal clinical setting.

BACKGROUND AND PURPOSE
The forces needed to move the ureteroscope up and down the urinary tract may injure the ureter, but a method to measure these forces in patients is lacking. The purpose of the study was to develop and test a novel method for measuring the pushing and pulling forces exerted on a semirigid ureteroscope during ureteroscopy (URS) in a clinical setting.


MATERIALS AND METHODS
During 2010 to 2011, 20 patients planned for retrograde flexible URS or percutaneous lithotripsy for renal pelvic stones were recruited to a study measuring the forces exerted on a semirigid ureteroscope during retrograde URS. A coupling device was constructed to connect a digital force meter to a standard semirigid ureteroscope. The pushing and pulling forces, given in Newton (N), were measured at four defined locations in the ureter. The experiment was repeated twice to evaluate the reproducibility of the results. Paired-samples t test and Intraclass Correlation Coefficient (ICC) addressed the reproducibility of the results.


RESULTS
The force meter did not disturb the endoscopic procedure, and the force measurements were performed as intended. The results were reproducible at repeated measurements, with the ICC ranging from minimum 0.737 to maximum 0.812 at the different measuring locations in the ureter. The mean forces needed for insertion of the ureteroscope increased from 4.4 N (±3.6 N) at the distal part of the ureter to 9.7 N (±7.3 N) at the proximal part with large interpatient variation. Similar but smaller forces were found for retraction.


CONCLUSION
The present method is proven to reliably measure forces exerted on the ureteroscope in a clinical setting. This opens the opportunity for further force studies on endoscopic procedures to make URS safer.