title: Postural Consequences of Cervical Sagittal Imbalance: A Novel Laboratory Model.
abstract: METHODS
  A biomechanical study using human spine specimens.
  
  
  OBJECTIVE
  To study postural compensations in lordosis angles that are necessary to maintain horizontal gaze in the presence of forward head posture and increasing T1 sagittal tilt.
  
  
  BACKGROUND
  Forward head posture relative to the shoulders, assessed radiographically using the horizontal offset distance between the C2 and C7 vertebral bodies (C2-C7 [sagittal vertical alignment] SVA), is a measure of global cervical imbalance. This may result from kyphotic alignment of cervical segments, muscle imbalance, as well as malalignment of thoracolumbar spine.
  
  
  METHODS
  Ten cadaveric cervical spines (occiput-T1) were tested. The T1 vertebra was anchored to a tilting and translating base. The occiput was free to move vertically but its angular orientation was constrained to ensure horizontal gaze regardless of sagittal imbalance. A 5-kg mass was attached to the occiput to mimic head weight. Forward head posture magnitude and T1 tilt were varied and motions of individual vertebrae were measured to calculate C2-C7 SVA and lordosis across C0-C2 and C2-C7.
  
  
  RESULTS
  Increasing C2-C7 SVA caused flexion of lower cervical (C2-C7) segments and hyperextension of suboccipital (C0-C1-C2) segments to maintain horizontal gaze. Increasing kyphotic T1 tilt primarily increased lordosis across the C2-C7 segments. Regression models were developed to predict the compensatory C0-C2 and C2-C7 angulation needed to maintain horizontal gaze given values of C2-C7 SVA and T1 tilt.
  
  
  CONCLUSIONS
  This study established predictive relationships between radiographical measures of forward head posture, T1 tilt, and postural compensations in the cervical lordosis angles needed to maintain horizontal gaze. The laboratory model predicted that normalization of C2-C7 SVA will reduce suboccipital (C0-C2) hyperextension, whereas T1 tilt reduction will reduce the hyperextension in the C2-C7 segments. The predictive relationships may help in planning corrective strategy in patients experiencing neck pain, which may be attributed to sagittal malalignment.
  
  
  METHODS
  N/A.
authors.affiliation: *Edward Hines, Jr. VA Hospital, Hines, IL †Loyola University Stritch School of Medicine, Maywood, IL ‡Governors State University, University Park, IL §Northwestern University Feinberg School of Medicine, Chicago, IL; and ¶Wentworth Spine Clinic, Sydney, NSW, Australia.
authors.forename: Avinash G
authors.initials: AG
authors.lastname: Patwardhan
authors.forename: Robert M
authors.initials: RM
authors.lastname: Havey
authors.forename: Saeed
authors.initials: S
authors.lastname: Khayatzadeh
authors.forename: Muturi G
authors.initials: MG
authors.lastname: Muriuki
authors.forename: Leonard I
authors.initials: LI
authors.lastname: Voronov
authors.forename: Gerard
authors.initials: G
authors.lastname: Carandang
authors.forename: Ngoc-Lam
authors.initials: NL
authors.lastname: Nguyen
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Ghanayem
authors.forename: Dale
authors.initials: D
authors.lastname: Schuit
authors.forename: Alpesh A
authors.initials: AA
authors.lastname: Patel
authors.forename: Zachary A
authors.initials: ZA
authors.lastname: Smith
authors.forename: William
authors.initials: W
authors.lastname: Sears
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D002102:Cadaver; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006257:Head; D006801:Humans; D008141:Lordosis / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008875:Middle Aged; D011187:Posture; D011859:Radiography; D016059:Range of Motion, Articular; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging; D055815:Young Adult