title: Cervical pedicle screw placement using the "key slot technique": the feasibility and learning curve.
abstract: METHODS
  A retrospective study.
  
  
  OBJECTIVE
  To present the accuracy and safety of a novel "key slot (KS)" technique for cervical pedicle screw (CPS) placement with the learning curve.
  
  
  BACKGROUND
  Safety and learning curve are the issues preventing wide acceptance of CPS. On the basis of the local anatomy of the pedicle, the authors modified the conventional technique to increase the accuracy and comfortableness of CPS placement with minimal bone loss.
  
  
  METHODS
  A total of 277 subaxial CPS in 50 patients had been inserted using author's technique were reviewed. The KS-shaped entry was created on the medial half of the lateral mass with a 3 mm cutting burr. The shape of entry was a right-angled triangle on the axial plane. The apex of triangle was the virtual pedicle inlet and the oblique side was same as pedicle axis. After making entry, the pedicle was probed with a curved awl along the medial wall. On the postoperative vascular-enhanced computed tomography scan, we analyzed the direction and grade of pedicle perforation (grade 0: no perforation, 1:< 25%, 2: 20% to 50%, 3: > 50% of screw diameter) on the chronological group of consecutive 10 cases. Grade 2 and 3 were considered as incorrect position.
  
  
  RESULTS
  The correct position was found in 250 screws (90.3%); grade 0 - 215 screws, 1 - 35 screws and the incorrect position in 27 screws (9.7%); grade 2 - 21 screws, grade 3 - 6 screws. The incidence of incorrect screw position was 18% in the initial 20 cases and 2.7% after that. There was no neurovascular complication related with CPS.
  
  
  CONCLUSIONS
  We performed CPS placement using the KS technique and with 90% correct position without clinical complications. After the learning curve, the incidence was 2.7%. This technique could be considered relatively concrete and safe modification of conventional technique with minimal bone loss.
authors.affiliation: Department of Orthopedic Surgery, Kyung Hee University Hospital at Gangdong, Seoul, Korea. shl6@khu.ac.kr
authors.forename: Sang-Hun
authors.initials: SH
authors.lastname: Lee
authors.forename: Ki-Tack
authors.initials: KT
authors.lastname: Kim
authors.forename: Kuniyoshi
authors.initials: K
authors.lastname: Abumi
authors.forename: Kyung-Soo
authors.initials: KS
authors.lastname: Suk
authors.forename: Jung Hee
authors.initials: JH
authors.lastname: Lee
authors.forename: Kyung-Jun
authors.initials: KJ
authors.lastname: Park
mesh_terms: D000328:Adult; D000368:Aged; D001863:Bone Screws; D002574:Cervical Vertebrae / Q000601:surgery*; D019299:Decompression, Surgical / Q000295:instrumentation* / Q000379:methods; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007431:Intraoperative Complications / Q000453:epidemiology / Q000517:prevention & control; D059032:Learning Curve; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D012189:Retrospective Studies; D013117:Spinal Cord Compression / Q000209:etiology / Q000601:surgery; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D013126:Spinal Nerve Roots / Q000293:injuries; D025321:Surgery, Computer-Assisted / Q000379:methods*; D014057:Tomography, X-Ray Computed; D014711:Vertebral Artery / Q000293:injuries; D055815:Young Adult