title: An assessment of the most reliable method to estimate the sagittal alignment of the cervical spine: analysis of a prospective cohort of 138 cases.
abstract: OBJECTIVE Although there is increasing recognition of the importance of cervical spinal sagittal balance, there is a lack of consensus as to the optimal method to accurately assess the cervical sagittal alignment. Cervical alignment is important for surgical decision making. Sagittal balance of the cervical spine is generally assessed using one of two methods; namely, measuring the angle between C-2 and C-7, and drawing a line between C-2 and C-7. Here, the best method to assess sagittal alignment of the cervical spine is investigated. METHODS Data from 138 patients enrolled in a randomized controlled trial (Procon) were analyzed. Two investigators independently measured the angle between C-2 and C-7 by using Harrison's posterior tangent method, and also estimated the shape of the sagittal curve by using a modified Toyama method. The mean angles of each quantitative assessment of the sagittal alignment were calculated and the results were compared. The interrater reliability for both methods was estimated using Cronbach's alpha. RESULTS For both methods the interrater reliability was high: for the posterior tangent method it was 0.907 and for the modified Toyama technique it was 0.984. For a lordotic cervical spine, defined by the modified Toyama method, the mean angle (defined by Harrison's posterior tangent method) was 23.4° ± 9.9° (range 0.4°-52.4°), for a kyphotic cervical spine it was -2.2° ± 9.2° (range -16.1° to 16.9°), and for a straight cervical spine it was 10.5° ± 8.2° (range -11° to 36°). CONCLUSIONS An absolute measurement of the angle between C-2 and C-7 does not unequivocally define the sagittal cervical alignment. As can be seen from the minimum and maximum values, even a positive angle between C-2 and C-7 could be present in a kyphotic spine. For this purpose, the modified Toyama method (drawing a line from the posterior inferior part of the vertebral body of C-2 to the posterior upper part of the vertebral body of C-7 without any measurements) is a better tool for a global assessment of cervical sagittal alignment. Clinical trial registration no.: ISRCTN41681847 ( https://www.isrctn.com ).
authors.affiliation: Department of Orthopedic Surgery, Via Sana Clinics, Mill.
authors.forename: Roland D
authors.initials: RD
authors.lastname: Donk
authors.affiliation: Division of Neurosurgery and Spinal Program, Department of Surgery, University of Toronto, Ontario, Canada.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Fehlings
authors.affiliation: Department of Neurology, Canisius Wilhelmina Hospital, Nijmegen; and.
authors.forename: Wim I M
authors.initials: WIM
authors.lastname: Verhagen
authors.affiliation: Departments of 4 Neurosurgery and.
authors.forename: Hisse
authors.initials: H
authors.lastname: Arnts
authors.affiliation: Health Evidence, Radboud University Medical Center, Nijmegen, The Netherlands ; and.
authors.forename: Hans
authors.initials: H
authors.lastname: Groenewoud
authors.affiliation: Health Evidence, Radboud University Medical Center, Nijmegen, The Netherlands ; and.
authors.forename: André L M
authors.initials: ALM
authors.lastname: Verbeek
authors.affiliation: Departments of 4 Neurosurgery and.
authors.forename: Ronald H M A
authors.initials: RHMA
authors.lastname: Bartels
mesh_terms: D000293:Adolescent; D000328:Adult; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging* / Q000601:surgery; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007738:Kyphosis / Q000000981:diagnostic imaging / Q000601:surgery; D008141:Lordosis / Q000000981:diagnostic imaging / Q000601:surgery; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D015203:Reproducibility of Results; D055815:Young Adult
keywords: SVA = sagittal vertical axis; cervical spine; kyphosis; lordosis; sagittal alignment