Re: Which Is More Important in Predicting the Outcome of Extracorporeal Shockwave Lithotripsy of Solitary Renal Stones: Stone Location or Stone Burden? (From: Khalil MM. J Endourol 2012;26:535–539.)

W e read with interest this article on shockwave lithotripsy (SWL). The authors have used different parameters such as number of sessions, number of shockwaves used, and re-treatment rate to describe the effectiveness of treatment. While the authors found a statistical significance in the mean number of sessions and the mean number of shockwaves needed for treatment of stones located in the renal pelvis, lower calix, middle calix, and upper calix, they did not find statistical significance in the re-treatment rate (for different locations). This play of statistics makes interpretation of data difficult.

In the authors' opinion, what was the reason why stones in the lower calix needed more shockwaves for fragmentation? Because the stone composition in different locations was likely to be the same and also because the stone size between different locations was similar, the number of shockwaves used for fragmentation should likely be same for all groups. As we know, only the clearance rate for stones in the inferior calix is poor (as compared with stones in other locations) and not the fragmentation rate.

In the Discussion section (third last paragraph), the authors wrongly mention, “In the current study, there was a statistically significant increase in the stone-free rate with increase of stone burden;….” In the same paragraph, second line, the authors (again) wrongly state that “The stone-free rate in different calices was also found to be higher with increasing stone burden;…”