Does the Prone Position During the Shockwave Lithotripsy of Kidney Stones Improve the Stone-Free Rate? Results from a Randomized Clinical Trial

This study aimed to evaluate the impact of the skin-to-stone distance in the supine and prone positions on the outcome of shockwave lithotripsy of kidney stones.

In a prospective randomized clinical trial study, 81 patients that candidates for shockwave lithotripsy (SWL) of kidney stones were randomly divided into two groups to perform SWL in the prone position (40 patients) or conventional supine position (41 patients). Demographic data, stone characteristics, skin–to–stone distances (SSD) in CT, SSD during SWL with an ultrasound probe in prone and supine positions, total shock wave rate, total energy (kilovolt), visual analog scale (VAS), complications (Clavien-Dindo scale system), and SWL success rate evaluated in two intervention and control groups. All statistical analysis was performed by independent T-test, Chi-Square test, Fisher exact test, paired T-test, and SPSS 22.0 software for windows.

There were no significant differences between demographic characteristics, SWL sessions, the median number of SWLs, the median SWL time, median total energy, VAS, and complications in the two groups. The SFR was numerically higher in the prone SWL group than in the supine SWL group (80% vs. 73.2%) but was not significantly different (P = 0.468). Also, the inline ultrasound (US) measuring of the SSD in the prone position was significantly different from US SSD measures in the supine position in the two groups (Ps = 0.001 and 0.024). The mean SSD was lower in the US measurement during the SWL process that measured in supine and prone position than the CT measurement (73.5 vs. 101.1), which means the routine SSD measured by CT scan is higher than SSD in the US probe measurement during SWL.

The prone position SWL modification could be effective in obese patients with a BMI of more than 30 and increase the stone-free rate (P=0.039) with a similar safety profile and comparable VAS score. It seems the SSD measured by the ultrasound is a more accurate dynamic measurement during the SWL and needs to define the SSD according to the SSD calculation by the US probe of the therapy head. SFR was numerically higher in the prone compared with the supine treatment groups