title: Is C1 lateral mass screw placement safe for the Chinese, Indians, and Malays? An analysis of 180 computed tomography scans.
abstract: C1 lateral mass (C1LM) screw is a common procedure in spine surgery. However, related studies are lacking in Asia. We aim to determine the safety of C1LM screw for the Chinese, Indians, and Malays.
  
  
  
  Three-dimensional computed tomographies of 180 subjects (60 from each ethnic) were analyzed. The length and angulations of C1LM screw and the location of internal carotid artery (ICA) in relation to C1LM were assessed and classified according to the classification by Murakami et al. The incidence of ponticulus posticus (PP) was determined and the differences among the population of these three ethnics were recorded.
  
  
  
  The average base length was 8.5 ± 1.4 mm. The lengths within the lateral mass were between 14.7 ± 1.6 mm and 21.7 ± 2.3 mm. The prevalence of PP was 8.3%. 55.3% (199) of ICA were located in zone 0, 38.3% (138) in zone 1-1, 6.4% (23) in zone 1-2, and none in zone 1-3 and zone 2. The average angulation from the entry point to the ICA was 8.5° ± 6.4° laterally. The mean distance of ICA from C1 anterior cortex was 3.7 ± 1.7 mm (range: 0.6∼11.3). There was no difference in distribution of ICA in zone 1 among the three population (Chinese-47%, Indians-61%, and Malays-53%; p > 0.05).
  
  
  
  No ICA is located medial to the entry point of C1LM screw. If bicortical purchase of C1LM screw is needed, screw protrusion of less than 3 mm or medially angulated is safe for ICA. The incidence of PP is 8.3% with higher prevalence among the Indian population.
authors.affiliation: 1 NOCERAL, Department of Orthopedic Surgery, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia.
authors.forename: C K
authors.initials: CK
authors.lastname: Lee
authors.affiliation: 1 NOCERAL, Department of Orthopedic Surgery, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia.
authors.forename: T S
authors.initials: TS
authors.lastname: Tan
authors.affiliation: 1 NOCERAL, Department of Orthopedic Surgery, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia.
authors.forename: Cyw
authors.initials: C
authors.lastname: Chan
authors.affiliation: 1 NOCERAL, Department of Orthopedic Surgery, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia.
authors.forename: M K
authors.initials: MK
authors.lastname: Kwan
mesh_terms: D000328:Adult; D000368:Aged; D001863:Bone Screws; D001270:Cervical Atlas / Q000000981:diagnostic imaging / Q000601:surgery*; D002681:China / Q000208:ethnology; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D007194:India / Q000208:ethnology; D008296:Malaysia / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D013122:Spinal Diseases / Q000175:diagnosis / Q000208:ethnology / Q000601:surgery*; D013123:Spinal Fusion / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D055815:Young Adult
keywords: C1 lateral mass screw safety; C1 morphometry; Chinese; Indian; Malay; internal carotid artery; ponticulus posticus