Supine or prone percutaneous nephrolithotomy: do anatomical changes make it worse?

To evaluate the different anatomical properties and determine the risk of visceral organ injury in supine, prone, and prone-flex positions.

A total of 30 patients with renal stones >2 cm were included. A dose reduced abdominopelvic tomography in a supine, prone, and 30° prone-flex position was performed. The access tract length, subcutaneous tissue length, nearest organ distance, maximum access angle, access field, and the degree of renal displacement were measured in axial and coronal images. The parameters were analyzed by the paired t-test and Wilcoxon signed test according to normalcy analysis.

The mean tract lengths and the subcutaneous fat tissue lengths in the lower, middle, and upper poles of kidney were significantly longer in the supine position. The significance of access tract lengths had disappeared when we subtracted the subcutaneous fat tissue length from the whole tract length, exhibiting that the main determinant of tract length was subcutaneous tissue thickness. The maximum access angles were 96.7±22.0°, 94.2±23.6°, and 89.1±23.9° in the supine, prone, and prone-flex position, respectively (p>0.05). The access field was shorter in the supine (80.8±13.3 mm) than prone (86.3±15.0 mm) and prone-flex (86.7±18.4 mm) position (p<0.001). The nearest organ distance to access tract was similar between the supine and prone position in every pole of kidney.

The anatomical changes related to supine positioning does not increase the risk of percutaneous nephrolithotomy (PCNL) complications. Although supine PCNL may have some benefits over prone PCNL, there will also be some technical difficulties related to the surgeon's manipulations, which are related with the longer access tract and more limited access field.