title: Quantitative Anatomy of C7 Vertebra in Southern Chinese for Insertion of Lateral Mass Screws and Pedicle Screws.
abstract: METHODS
  Retrospective study.
  
  
  OBJECTIVE
  To analyze the quantitative anatomy of C7 vertebra for insertion of lateral mass screws and pedicle screws in Southern Chinese patients.
  
  
  BACKGROUND
  C7 lateral mass is smaller when compared to other subaxial cervical levels, which limits the length of lateral mass screws that can be used. Some studies have suggested pedicle screws for better fixation. But, this option is limited by the narrow pedicle width.
  
  
  METHODS
  We have obtained computed tomography (CT) cervical spine data in 0.625 mm slices from our radiology department. The patients were adults. CTs were from May to August, 2015. The lateral mass screw length was measured using Margerl's technique and pedicle width and pedicle screw trajectory were determined in three-dimensional reformated images.
  
  
  RESULTS
  CT scans of cervical spines of 94 patients were obtained and 188 lateral masses and pedicles of C7 vertebrae were measured. The mean lateral mass screw length was 13.2 mm (standard deviation [SD] 1.6 mm), mean outer pedicle width was 5.9 mm (SD 1.0 mm) and mean pedicle screw trajectory was 29.4 degrees (SD 3.6 degrees). Most (91.0%) of the pedicles had an outer diameter ≥4.5 mm.
  
  
  CONCLUSIONS
  The mean lateral mass screw length was longer when compared with other similar studies, while the mean outer pedicle width was narrower. Nearly 10% of the pedicles were unable to accommodate 3.5 mm screws. These findings favor the use of lateral mass screws to provide a safe and stable fixation for C7 vertebrae in Southern Chinese patients, while the final choice of fixation method should only be confirmed after careful preoperative planning with CT scan.
authors: Department of Orthopaedics and Traumatology, Kwong Wah Hospital, Hong Kong.
authors: Michael Siu Hei
authors: MS
authors: Tse
authors: Department of Diagnostic and Interventional Radiology, Kwong Wah Hospital, Hong Kong.
authors: Chi Hin
authors: CH
authors: Chan
authors: Department of Orthopaedics and Traumatology, Kwong Wah Hospital, Hong Kong.
authors: Kam Kwong
authors: KK
authors: Wong
authors: Department of Orthopaedics and Traumatology, Kwong Wah Hospital, Hong Kong.
authors: Wing Cheung
authors: WC
authors: Wong
keywords: Cervicalvertebrae; Instrumentation; Pedicle screws