Calcium phosphate content does not affect stone-free rate after percutaneous nephrolithotomy

Purpose: Recent research suggests that the stone-free rate for percutaneous nephrostolithotomy is lower in patients with calcium phosphate stones than in those with stones of other compositions. We reviewed our percutaneous nephrostolithotomy outcomes to investigate this unexplained finding. Materials and Methods: A total of 188 patients with sufficient data available for review underwent unilateral percutaneous nephrostolithotomy at our institution between September 2005 and May 2007. Patients were analyzed based on stone burden (including 2 cm or less, greater than 2 cm, partial staghorn calculus and complete staghorn calculus). Stones were also stratified by calcium phosphate content (0%, 1% to 10%, 11% to 60% and greater than 60%). To remain consistent with the previous study procedural failure was classified as greater than 2 mm residual stone fragments identified by unenhanced computerized tomography on postoperative day 1 regardless of the ultimate stone-free rate after secondary procedures. Multivariate logistic regression analysis was done to identify factors predicting a failed procedure. Results: Of the patients 101 (54%) were male and 132 (71%) were recurrent stone formers. Overall 107 cases (57%) had calcium phosphate as a stone component and 37.8% were classified as failures. Increasing stone size was associated with a decreased stone-free rate (p = 0.009). The failure rate was 37%, 46.4%, 38.1% and 32.4% for patients with a 0%, 1% to 10%, 11% to 60% and greater than 60% calcium phosphate stone content (p = 0.68). On multivariate logistic regression analysis no association was noted between calcium phosphate content and greater than 2 mm residual stones (p = 0.67). Conclusions: Calcium phosphate stone composition does not predict a poor stone-free rate after percutaneous nephrostolithotomy.