Predictors of excessive renal displacement during access in percutaneous nephrolithotomy: a randomized clinical trial.

To determine the magnitude of renal displacement (a major cause of access failure or loss) during the renal access steps in percutaneous nephrolithotomy (PCNL), investigate predictors of excessive renal displacement, and compare the effect of one-stage versus gradual dilation on renal displacement during access. Sixty-six adult patients undergoing PCNL were randomized into two groups containing 33 patients each: Group 1 underwent gradual tract dilation with Alken metal dilators, and Group 2 received one-stage tract dilation. In each patient, maximum renal displacement was measured in three planes (cephalocaudal, anteroposterior, and mediolateral) during the three access steps (needle puncture, Alken guide insertion, and dilator advancement). The patients' demographic data and intraoperative parameters were compared. In both groups, net renal displacement during the three access steps was in the cephalad, medial, and anterior directions. There were no significant differences in the magnitude of renal displacement in patients with gradual versus one-stage tract dilation. Renal displacement was significantly more pronounced in all planes and in all access steps in female patients and in those with no previous history of open stone surgery on the ipsilateral kidney. High body mass index (BMI) showed a significant negative correlation with cephalad and anterior renal displacement, but not with medial displacement. Three-dimensional movement of the kidney during percutaneous access in PCNL is similar when gradual versus one-stage tract dilation is used. Inherent patient characteristics, such as female sex, BMI, and a previous ipsilateral flank scar are major determinants of the magnitude of renal displacement during the PCNL access steps.