title: Percutaneous nephrolithotomy in the prone and prone-flexed positions: anatomic considerations.
abstract: OBJECTIVE
  Percutaneous nephrolithotomy is commonly performed in the prone position. Knowledge of renal anatomy and the relationship of adjacent organs is essential to minimize patient morbidity and iatrogenic organ injury. We present the anatomical basis for a prone-flexed modification to patient positioning and review the advantages and disadvantages of alternate positions.
  
  
  METHODS
  Triphasic computed tomography was conducted with the patient in supine, prone, and prone-flexed positions, and an anatomical survey was conducted. A 30 degrees angle was used to approximate the plane of nephrostomy access and the risk of organ injury.
  
  
  RESULTS
  For upper pole punctures, the liver and spleen were more medially situated, and thus more likely to be injured with supine positioning, compared with either prone or prone-flexed positioning (p < 0.001). In contrast, for lower pole punctures, the colon was more medially situated in the prone and prone-flexed positions compared to supine (p < 0.001). With prone-flexed positioning, the left kidney was displaced lower than the right in 92.3% of cases. The prone-flexed modification increased the distance from the posterior iliac crest to the 12th and 11th ribs by 2.9 and 3.0 cm, respectively (p < 0.001). If access was performed in the most superior calyx, this would have converted an upper pole access above the 11th rib to one above the 12th rib in 5 of 11 patients (45.5%).
  
  
  CONCLUSIONS
  Prone-flexed positioning is a simple modification that provides improved access to the upper pole and more mobility for lower pole percutaneous nephrolithotomy. This position is well tolerated and has several advantages over other patient positions, including the supine position.
authors.affiliation: Department of Surgery, St. Michael's Hospital, University of Toronto , Toronto, Canada.
authors.forename: A Andrew
authors.initials: AA
authors.lastname: Ray
authors.forename: Dae-Gyun
authors.initials: DG
authors.lastname: Chung
authors.forename: R John D'A
authors.initials: RJ
authors.lastname: Honey
mesh_terms: D006801:Humans; D007668:Kidney / Q000033:anatomy & histology; D009403:Nephrostomy, Percutaneous / Q000379:methods*; D056888:Patient Positioning / Q000379:methods*; D016684:Prone Position