Purpose: We examined the effects of probe rotation and pressure on stone fragmentation in an in vitro percutaneous nephrolithotomy model.
Materials and methods: The study was a fully randomized, factorial experiment with 20 repeat trials performed at each combination of variables, yielding a total of 300 trials per device for ultrasonic tests and 360 for ultrasonic/pneumatic combination tests. Varying masses were placed on the hand piece of each device to create a probe contact pressure of 400, 1,000 or 2,000 gm. The impact of rotation was tested only at 0 or 90 degrees and rotating only at a frequency of 2 Hz. Statistical analysis was performed using R, version 2.6.2.
Results: For the Cyberwand the Tukey HSD test showed that 400 and 1,000 gm probe pressure were significantly more effective than 2,000 gm pressure (p <0.05). The range and frequency of rotation were not statistically significant variables affecting Cyberwand efficiency. For the LithoClast Ultra using only the ultrasonic probe significant differences were found among the 3 pressure levels (400, 1,000 and 2,000 gm, respectively, p <0.05). For rotation 90 degrees were significantly more effective than 0 degrees (p <0.05) at a mean +/- SD stone mass of 0.168 +/- 0.078 and 0.107 +/- 0.09 gm, respectively. For the LithoClast Ultra ultrasonic/pneumatic combination 1,000 gm pressure were significantly more effective than 400 or 2,000 gm (p <0.05). The 6 and 12 Hz pneumatic frequencies outperformed 3 Hz but were not significantly different from each other (p <0.05).
Conclusions: Differences in probe manipulation impact stone fragmentation efficiency and procedural success.