title: Free-hand pedicle screw placement during revision spinal surgery: analysis of 552 screws.
abstract: METHODS
  : A retrospective study.
  
  
  OBJECTIVE
  : To evaluate the safety of free-hand pedicle screw placement during revision surgery at levels with a solid posterior fusion mass and/or identified pseudarthroses of the thoracic and lumbosacral spine.
  
  
  BACKGROUND
  : Placement of pedicle screws into previous fusion masses or pseudarthrosis levels of the spine is challenging because of the loss of anatomic landmarks. We are aware of no study focusing on screw placement without any type of radiographic or navigational assistance.
  
  
  METHODS
  : Thirty-seven patients underwent revision spinal surgery with posterior spinal instrumentation and fusion using 552 transpedicular screws by a single surgeon from 1994 to 2003. Among 552 screws, 184 were inserted into virgin levels, 60 were inserted into the vertebral body through previous screw holes, 208 were inserted into fusion masses, and 100 were inserted into pseudarthrosis levels. We used the quadrangulation method to gain pedicle access in a prior fusion mass after diligent exposure of any and all visible anatomic landmarks. All screws were analyzed using radiographs, intraoperative monitoring data, and clinical outcomes.
  
  
  RESULTS
  : There were 29 women and 8 men. The mean age of patients at the time of surgery was 38 + 6 years (range, 8-75 years). Six screws were removed intraoperatively according to the triggered electromyography criteria and 4 of them were repositioned after checking the integrity of the pedicle by a careful probing technique (1.09%). Six screws were removed after checking the intraoperative radiographs and 5 screws were misplaced, as noted, in postoperative radiographs (1.99%). Two patients underwent revision surgery at 3 days and 6 weeks after initial surgery, respectively, for root decompression at the osteotomy site although screw positions were correct.
  
  
  CONCLUSIONS
  : The free-hand technique of thoracic and lumbosacral pedicle screw placement in revision spinal surgery is reliable and safe when using the quadrangulation method of gaining pedicle access in a prior fusion mass or at pseudarthrosis levels.
authors.affiliation: Hallym University Sacred Heart Hospital, Hallym University College of Medicine, Anyang, Korea.
authors.forename: Young-Woo
authors.initials: YW
authors.lastname: Kim
authors.forename: Lawrence G
authors.initials: LG
authors.lastname: Lenke
authors.forename: Yongjung J
authors.initials: YJ
authors.lastname: Kim
authors.forename: Keith H
authors.initials: KH
authors.lastname: Bridwell
authors.forename: Youngbae B
authors.initials: YB
authors.lastname: Kim
authors.forename: Kei
authors.initials: K
authors.lastname: Watanabe
authors.forename: Kota
authors.initials: K
authors.lastname: Watanabe
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001863:Bone Screws; D002648:Child; D020878:Device Removal; D004576:Electromyography; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D010027:Osteotomy / Q000009:adverse effects; D011542:Pseudarthrosis / Q000000981:diagnostic imaging / Q000209:etiology / Q000601:surgery*; D011859:Radiography; D012086:Reoperation; D012189:Retrospective Studies; D013122:Spinal Diseases / Q000601:surgery*; D013123:Spinal Fusion / Q000009:adverse effects / Q000295:instrumentation*; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D017211:Treatment Failure