title: Anatomic considerations in lumbar posterolateral percutaneous procedures.
abstract: METHODS
  Intervertebral foraminal anatomy of L2-S1 was investigated by the anatomic dissection of 96 foraminal levels in 12 human cadaveric spines.
  
  
  OBJECTIVE
  The goal of this study was to determine the dimensions of the "safe zone" and a safe point of insertion in percutaneous intradiscal procedures and the largest safe working cannula diameter.
  
  
  BACKGROUND
  Working cannulas are used in percutaneous lumbar procedures. The dimensions of the safe zone of insertion and determination of the optimal cannula size based on these measurements and point of insertion are unclear from the literature.
  
  
  METHODS
  Safe zone dimensions from L2-L3 to L5-S1 were determined as were two cannula diameters, C1 and C2. C1 was the maximal cannula size that can be placed within the safe zone. C2 is the maximal size allowable when the point of insertion lies in the midline of the pedicle.
  
  
  RESULTS
  The average triangular safe zone was 18.9 mm wide and 12.3 mm high; the hypotenuse measured 23.0 mm. The maximum C1 diameter ranged 5.0-10.0 mm. The corresponding safe point of insertion lay along the medial one third of the pedicle. The maximum C2 diameter ranged 4.0-8.9 mm. The corresponding safe point of insertion lay in the midline of the pedicle.
  
  
  CONCLUSIONS
  Either a 7.5-mm cannula placed in line with the medial one third of the pedicle or a 6.3-mm cannula located in the midline of the pedicle appears safe.
authors.affiliation: Department of Orthopaedic Surgery, Northwestern University Medical School, Chicago, Illinois, USA.
authors.forename: S R
authors.initials: SR
authors.lastname: Mirkovic
authors.forename: D G
authors.initials: DG
authors.lastname: Schwartz
authors.forename: K D
authors.initials: KD
authors.lastname: Glazier
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002102:Cadaver; D002404:Catheterization; D017587:Diskectomy, Percutaneous / Q000295:instrumentation*; D006801:Humans; D007403:Intervertebral Disc / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000033:anatomy & histology* / Q000601:surgery; D008875:Middle Aged