title: Mapping occipital bone thickness using computed tomography for safe screw placement.
abstract: OBJECT Safe and effective insertion of occipital bone screws requires morphological analysis of the occipital bone, which is poorly documented in the literature. The authors of this study present morphological data for determining the area of screw placement for optimal internal fixation. METHODS The subjects of this institutional review board-approved retrospective study were 105 individuals without head and neck disease who underwent CT imaging at the authors' hospital. There were 55 males and 50 females, with a mean age of 57.1 years (range 20-91 years). Measurements using CT were taken according to a matrix of 55 points following a grid with 1-cm spacing based on the external occipital protuberance (EOP). RESULTS The maximum thickness of the occipital bone was at the level of the EOP at 16.4 mm. Areas with thicknesses > 8 mm were more frequent at the EOP and up to 2 cm in all directions, as well as up to 1 cm in all directions at a height of 1 cm inferiorly, and up to 3 cm from the EOP inferiorly. The male group tended to have a thicker occipital bone than the female group, and the differences were significant around the EOP. The ratio of the trabecular bone to the occipital bone thickness was > 30% in the central region. At positions more than 2 cm laterally, the ratio was < 15%, and the ratio gradually decreased further laterally. CONCLUSIONS Screws that are 8 mm long can be placed in the area extending 2 cm laterally from the EOP at the level of the superior nuchal line and approximately 3 cm inferior to the center. These results suggest that it may be possible to effectively insert a screw over a wider area than the conventional reference range.
authors.affiliation: Departments of 1 Orthopedic Surgery and.
authors.forename: Tomonori
authors.initials: T
authors.lastname: Morita
authors.affiliation: Departments of 1 Orthopedic Surgery and.
authors.forename: Tsuneo
authors.initials: T
authors.lastname: Takebayashi
authors.affiliation: Departments of 1 Orthopedic Surgery and.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Takashima
authors.affiliation: Departments of 1 Orthopedic Surgery and.
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Yoshimoto
authors.affiliation: Departments of 1 Orthopedic Surgery and.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Ida
authors.affiliation: Departments of 1 Orthopedic Surgery and.
authors.forename: Katsumasa
authors.initials: K
authors.lastname: Tanimoto
authors.affiliation: Public Health, Sapporo Medical University School of Medicine, Sapporo, Hokkaido; and.
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Ohnishi
authors.affiliation: Department of Orthopedic Surgery, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan.
authors.forename: Hiroyoshi
authors.initials: H
authors.lastname: Fujiwara
authors.affiliation: Department of Orthopedic Surgery, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan.
authors.forename: Masateru
authors.initials: M
authors.lastname: Nagae
authors.affiliation: Departments of 1 Orthopedic Surgery and.
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Yamashita
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001863:Bone Screws; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery; D005260:Female; D005593:Fracture Fixation, Internal / Q000379:methods; D006801:Humans; D008297:Male; D008875:Middle Aged; D009777:Occipital Bone / Q000000981:diagnostic imaging* / Q000601:surgery; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods; D055815:Young Adult
keywords: EOP = external occipital protuberance; ICC = intraclass correlation coefficient; morphological analysis; occipital bone; occipitocervical fusion; technique; thickness