title: Accuracy of pedicle screw placement for lumbar fusion using anatomic landmarks versus open laminectomy: a comparison of two surgical techniques in cadaveric specimens.
abstract: OBJECTIVE
  We determined whether the accuracy of lumbar pedicle screw placement is optimized by performing a laminectomy before screw placement with screw entry point and trajectory being guided by pedicle visualization and palpation (Technique 1). This technique was compared with a technique using anatomic landmarks for pedicle screw placement (Technique 2). The biomechanical stability of the instrumented constructs, in the absence and presence of a laminectomy, was also compared.
  
  
  METHODS
  Twelve L1-L3 specimens were harvested from fresh cadavers. The intact laminectomy and instrumented spines were biomechanically tested in flexion and extension, lateral bending, and axial rotation. Laminectomies were performed in six of the 12 specimens before pedicle screw placement using Technique 1. The remaining six specimens underwent pedicle screw and rod fixation using Technique 2. Computed tomographic images were obtained for all instrumented specimens. Deviation of the screws from the ideal entry point or trajectory was analyzed to quantitatively compare the two techniques.
  
  
  RESULTS
  Computed tomographic analysis of the specimens showed that all screw placements were within the pedicles. Scatter plot analysis demonstrated that screws placed using Technique 2 were more likely to have the combination of entry points and trajectories medial to the ideal entry point and trajectory. Laminectomy did not weaken the final pedicle screw and rod-fixated constructs.
  
  
  CONCLUSIONS
  All screw placements were grossly within the confines of the pedicles, regardless of technique, as evidenced by computed tomographic analysis. Furthermore, the anatomic landmark technique and the open laminectomy technique yielded biomechanically equivalent pedicle screw and rod-fixated constructs.
authors.affiliation: Department of Neurosurgery, Louisiana State University Health Sciences Center, Shreveport, Louisiana 71130-3932, USA.
authors.forename: Aftab
authors.initials: A
authors.lastname: Karim
authors.forename: Debi
authors.initials: D
authors.lastname: Mukherjee
authors.forename: Jorge
authors.initials: J
authors.lastname: Gonzalez-Cruz
authors.forename: Alan
authors.initials: A
authors.lastname: Ogden
authors.forename: Donald
authors.initials: D
authors.lastname: Smith
authors.forename: Anil
authors.initials: A
authors.lastname: Nanda
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena / Q000379:methods; D001863:Bone Screws / Q000592:standards*; D002102:Cadaver; D006801:Humans; D007431:Intraoperative Complications / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control; D007796:Laminectomy / Q000295:instrumentation* / Q000379:methods; D008159:Lumbar Vertebrae / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000601:surgery*; D008875:Middle Aged; D011183:Postoperative Complications / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control; D011300:Preoperative Care / Q000379:methods; D013115:Spinal Canal / Q000033:anatomy & histology / Q000601:surgery; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D014057:Tomography, X-Ray Computed / Q000379:methods / Q000592:standards