title: Prospective evaluation of outcome of percutaneous nephrolithotomy using the 'STONE' nephrolithometry score: A single-centre experience.
abstract: OBJECTIVE
  To assess the prediction of stone clearance and complications of percutaneous nephrolithotomy (PCNL) using the 'STONE' nephrolithometry score, assessing stone size, tract length (skin-to-stone distance), degree of obstruction, number of calyces involved and stone essence (density).
  
  
  METHODS
  This was a prospective study of patients undergoing single-tract PCNL while prone, conducted at a university hospital. All patients had non-contrast-enhanced computed tomography within 3 weeks of the procedure. Only patients with a unilateral procedure and radio-opaque stones were included. The five variables of the STONE nephrolithometry score were calculated before the procedure. The stone-free rates were assessed with a plain abdominal film at 4 weeks and complications were graded using the modified Clavien system.
  
  
  RESULTS
  In all, 107 patients were included in the final analysis. Overall, 80% of patients were rendered stone-free. Among the individual variables, a larger stone (P = 0.002) and the involvement of multiple calyces (P = 0.04) were associated with residual stones, while tract length (skin-to-stone distance), stone density and presence of hydronephrosis were not. Patients who were rendered stone-free had a statistically significant lower overall STONE score than those with residual stones, at 7.24 vs. 8.14 (P = 0.02). The score also correlated with operative duration, which was significantly longer with a higher STONE score (P = 0.03). The complication rate was 18% and most complications were Clavien grade 2, with bleeding requiring a blood transfusion (11 patients) being the commonest. There were no deaths within 30 days of surgery, but there was no correlation between the STONE score and complications.
  
  
  CONCLUSIONS
  The STONE nephrolithometry score is a simple and easy to apply system for predicting complexity in stone clearance with PCNL.
authors.affiliation: Section of Urology, Department of Surgery, Aga Khan University, Karachi, Pakistan.
authors.forename: Muhammad
authors.initials: M
authors.lastname: Farhan
authors.affiliation: Section of Urology, Department of Surgery, Aga Khan University, Karachi, Pakistan.
authors.forename: Syed M
authors.initials: SM
authors.lastname: Nazim
authors.affiliation: Department of Radiology, Aga Khan University, Karachi, Pakistan.
authors.forename: Basit
authors.initials: B
authors.lastname: Salam
authors.affiliation: Section of Urology, Department of Surgery, Aga Khan University, Karachi, Pakistan.
authors.forename: M Hammad
authors.initials: MH
authors.lastname: Ather
keywords: BMI, body mass index; CROES, Clinical Research Office of the Endo-Urological Society; NCECT, non-contrast-enhanced CT; Outcome; PCNL, percutaneous nephrolithotomy; Percutaneous nephrolithotomy; SFR, stone-free rate; Scoring system; Urolithiasis