title: Pars and pedicle fracture and screw loosening associated with cortical bone trajectory: a case series and proposed mechanism through a cadaveric study.
abstract: BACKGROUND
  Cortical bone trajectory (CBT) technique for pedicle screw placement in the lumbar spine has become more popular since its introduction in 2009. The distinct advantages of using the CBT technique involve increased screw purchase within the cortical bone and reduced surgical dissection. However, contrary to several favorable biomechanical results, there were anecdotal reports of clinical complications associated with CBT.
  
  
  OBJECTIVE
  This study aimed (1) to report on two unique pars and pedicle fracture cases involving the use of the CBT technique and (2) to perform a cadaveric pilot study to determine the possible mechanism for this fracture pattern.
  
  
  METHODS
  A case report and cadaveric study were carried out.
  
  
  METHODS
  After presenting two clinical cases, 19 fresh-frozen lumbar vertebrae were obtained from 8 cadavers. Pedicle screws were instrumented on each level using CBT under video recording. After the instrumentation, X-ray images were obtained, and anatomical dissections were performed.
  
  
  RESULTS
  To be able to reach a necessary angle for medial to lateral CBT trajectory, 13 out of 19 (68%) spinous processes had to be removed. There were a total of seven complications. One pars and pedicle fracture out of 37 trajectories (2.7%) and 6 out of 37 trajectory deviations (16.2%), which resulted in gross loosening, were observed.
  
  
  CONCLUSIONS
  The head of the pedicle screw impinging on the base of spinous process and lamina was observed in our cadaveric model. This mechanism could potentially explain both screw loosening and fractures associated with the CBT technique.
authors.affiliation: Department of Orthopaedic Surgery, School of Medicine, Loma Linda University Medical Center, 11406 Loma Linda Dr, Suite 213, Loma Linda, CA 92354, USA. Electronic address: md4spine@yahoo.com.
authors.forename: Wayne K
authors.initials: WK
authors.lastname: Cheng
authors.affiliation: Department of Orthopaedic Surgery, School of Medicine, Loma Linda University Medical Center, 11406 Loma Linda Dr, Suite 213, Loma Linda, CA 92354, USA.
authors.forename: Yusuf T
authors.initials: YT
authors.lastname: Akpolat
authors.affiliation: Department of Orthopaedic Surgery, School of Medicine, Loma Linda University Medical Center, 11406 Loma Linda Dr, Suite 213, Loma Linda, CA 92354, USA.
authors.forename: Serkan
authors.initials: S
authors.lastname: İnceoğlu
authors.affiliation: Department of Orthopaedic Surgery, School of Medicine, Loma Linda University Medical Center, 11406 Loma Linda Dr, Suite 213, Loma Linda, CA 92354, USA.
authors.forename: Shalin
authors.initials: S
authors.lastname: Patel
authors.affiliation: Department of Orthopaedic Surgery, School of Medicine, Loma Linda University Medical Center, 11406 Loma Linda Dr, Suite 213, Loma Linda, CA 92354, USA.
authors.forename: Olumide A
authors.initials: OA
authors.lastname: Danisa
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery; D008297:Male; D008875:Middle Aged; D065289:Pedicle Screws / Q000009:adverse effects*; D011475:Prosthesis Failure / Q000209:etiology*; D013123:Spinal Fusion / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods
keywords: Complication; Cortical bone trajectory; Pars fracture; Pedicle fracture; Pedicle screw instrumentation; Screw loosening