title: Predicting Cervical Alignment Required to Maintain Horizontal Gaze Based on Global Spinal Alignment.
abstract: METHODS
  A retrospective cohort.
  
  
  OBJECTIVE
  The aim of this study was to investigate the cervical alignment necessary for the maintenance of horizontal gaze that depends on underlying thoracolumbar alignment.
  
  
  BACKGROUND
  Cervical Sagittal Curve (CC) is affected by thoracic and global alignment. Recent studies suggest large variability in normative CC ranging from lordotic to kyphotic alignment. No previous studies have assessed the effect of global spinal alignment on CC in maintenance of horizontal gaze.
  
  
  METHODS
  Patients without previous history of spinal surgery and able to maintain their horizontal gaze while undergoing full body imaging were included. Patients were stratified on the basis of thoracic kyphosis (TK) into (<30, 30-40, 40-50, and >50) and then by SRS-Schwab sagittal vertical axis (SVA) modifier into (posterior alignment SVA <0, aligned 0-50, and malaligned >50 mm). Cervical alignment was assessed among SVA grade in TK groups. Stepwise linear regression analysis was applied on random selection of 60% of the population. A simplified formula was developed and validated on the remaining 40%.
  
  
  RESULTS
  In each TK group (n = 118, 137, 125, 197), lower CC (C2-C7) was significantly more lordotic by increased Schwab SVA grade. T1 slope and cervical SVA significantly increased with increased thoracolumbar (C7-S1) SVA. Upper CC (C0-C2) and mismatch between T1 slope and CC (T1-CL) were similar. Regression analysis revealed LL minus TK (LL-TK) as an independent predictor (r = 0.640, r = 0.410) with formula: CC = 10- (LL-TK)/2. Validation revealed that the absolute difference between the predicted CC and the actual CC was 8.5°. Moreover, 64.2% of patients had their predicted C2-C7 values within 10° of the actual CC.
  
  
  CONCLUSIONS
  Cervical kyphosis may represent normal alignment in a significant number of patients. However, in patients with SVA >50 and greater thoracic kyphosis, cervical lordosis is needed to maintain the gaze. Cervical alignment can be predicted from underlying TK and lumbar lordosis, which may be clinically relevant when considering correction for thoracolumbar or cervical deformityLevel of Evidence: 3.
authors.affiliation: Spine Service, Hospital for Special Surgery, New York, NY.
authors.forename: Bassel G
authors.initials: BG
authors.lastname: Diebo
authors.affiliation: Spine Unit 1, Orthopedic Surgery Department, Bordeaux University Hospital, Bordeaux, France.
authors.forename: Vincent
authors.initials: V
authors.lastname: Challier
authors.affiliation: Department of Orthopaedic Surgery, NYU Langone Medical Center, New York, NY.
authors.forename: Jensen K
authors.initials: JK
authors.lastname: Henry
authors.affiliation: Department of Orthopaedic Surgery, NYU Langone Medical Center, New York, NY.
authors.forename: Jonathan H
authors.initials: JH
authors.lastname: Oren
authors.affiliation: Department of Orthopaedic Surgery, NYU Langone Medical Center, New York, NY.
authors.forename: Matthew Adam
authors.initials: MA
authors.lastname: Spiegel
authors.affiliation: Department of Orthopaedic Surgery, NYU Langone Medical Center, New York, NY.
authors.forename: Shaleen
authors.initials: S
authors.lastname: Vira
authors.affiliation: Memorial Sloan Kettering Cancer Center, New York, NY.
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Tanzi
authors.affiliation: Spine Service, Hospital for Special Surgery, New York, NY.
authors.forename: Barthelemy
authors.initials: B
authors.lastname: Liabaud
authors.affiliation: Spine Service, Hospital for Special Surgery, New York, NY.
authors.forename: Renaud
authors.initials: R
authors.lastname: Lafage
authors.affiliation: Department of Orthopaedic Surgery, NYU Langone Medical Center, New York, NY.
authors.forename: Themistocles S
authors.initials: TS
authors.lastname: Protopsaltis
authors.affiliation: Department of Orthopaedic Surgery, NYU Langone Medical Center, New York, NY.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Errico
authors.affiliation: Spine Service, Hospital for Special Surgery, New York, NY.
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Schwab
authors.affiliation: Spine Service, Hospital for Special Surgery, New York, NY.
authors.forename: Virginie
authors.initials: V
authors.lastname: Lafage
mesh_terms: D002574:Cervical Vertebrae / Q000473:pathology / Q000601:surgery*; D005260:Female; D006801:Humans; D007738:Kyphosis / Q000601:surgery*; D008141:Lordosis / Q000175:diagnosis / Q000601:surgery*; D008297:Male; D009333:Neck / Q000601:surgery; D012189:Retrospective Studies; D012600:Scoliosis / Q000601:surgery*; D013904:Thoracic Vertebrae / Q000601:surgery*