title: Computational anatomy of the dens axis evaluated by quantitative computed tomography: Implications for anterior screw fixation.
abstract: The surgical fracture fixation of the odontoid process (dens) of the second cervical vertebra (C2/axis) is a challenging procedure, particularly in elderly patients affected by bone loss, and includes screw positioning close to vital structures. The aim of this study was to provide an extended anatomical knowledge of C2, the bone mass distribution and bone loss, and to understand the implications for anterior screw fixation. One hundred and twenty standard clinical quantitative computed tomography (QCT) scans of the intact cervical spine from 60 female and 60 male European patients, aged 18-90 years, were used to compute a three-dimensional statistical model and an averaged bone mass model of C2. Shape and size variability was assessed via principal component analysis (PCA), bone mass distribution by thresholding and via virtual core drilling, and the screw placement via virtual positioning of screw templates. Principal component analysis (PCA) revealed a highly variable anatomy of the dens with size as the predominant variation according to the first principal component (PC) whereas shape changes were primarily described by the remaining PCs. The bone mass distribution demonstrated a characteristic 3D pattern, and remained unchanged in the presence of bone loss. Virtual screw positioning of two 3.5 mm dens screws with a 1 mm safety zone was possible in 81.7% in a standard, parallel position and in additional 15.8% in a twisted position. The approach permitted a more detailed anatomical assessment of the dens axis. Combined with a preoperative QCT it may further improve the diagnostic procedure of odontoid fractures. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2154-2163, 2017.
authors.affiliation: AO Research Institute Davos, Clavadelerstrasse 8, 7270 Davos, Switzerland.|Department of Trauma, Hand and Reconstructive Surgery, University Hospital Münster, Münster, Germany.
authors.forename: Dominic
authors.initials: D
authors.lastname: Gehweiler
authors.affiliation: Department of Trauma, Hand and Reconstructive Surgery, University Hospital Münster, Münster, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Wähnert
authors.affiliation: Department of Clinical Radiology, University Hospital Münster, Münster, Germany.
authors.forename: Norbert
authors.initials: N
authors.lastname: Meier
authors.affiliation: Department of Orthopedic Surgery, Sint Maartenskliniek, Nijmegen, The Netherlands.
authors.forename: Maarten
authors.initials: M
authors.lastname: Spruit
authors.affiliation: Department of Trauma, Hand and Reconstructive Surgery, University Hospital Münster, Münster, Germany.
authors.forename: Michael Johannes
authors.initials: MJ
authors.lastname: Raschke
authors.affiliation: AO Research Institute Davos, Clavadelerstrasse 8, 7270 Davos, Switzerland.
authors.forename: Robert Geoff
authors.initials: RG
authors.lastname: Richards
authors.affiliation: AO Research Institute Davos, Clavadelerstrasse 8, 7270 Davos, Switzerland.
authors.forename: Hansrudi
authors.initials: H
authors.lastname: Noser
authors.affiliation: AO Research Institute Davos, Clavadelerstrasse 8, 7270 Davos, Switzerland.
authors.forename: Lukas
authors.initials: L
authors.lastname: Kamer
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001368:Axis, Cervical Vertebra / Q000000981:diagnostic imaging* / Q000293:injuries; D015519:Bone Density; D001863:Bone Screws; D005260:Female; D005593:Fracture Fixation, Internal; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012189:Retrospective Studies; D016103:Spinal Fractures / Q000601:surgery; D014057:Tomography, X-Ray Computed; D055815:Young Adult
keywords: 3D statistical modelling; dens axis; quantitative computed tomography; virtual screw positioning; volumetric bone mineral density