title: Cervical sagittal alignment in adult hyperkyphosis treated by posterior instrumentation and in situ bending.
abstract: In the normal adult spine, a link between thoracolumbar and cervical sagittal alignment exists, suggesting adaptive cervical positional changes allowing horizontal gaze. In patients with thoracic hyperkyphosis, cervical adaptation to sagittal global alignment might be different from healthy individuals. However, this relationship has not clearly been reported in hyperkyphotic deformity.
  
  
  
  The purpose of this study was to identify cervical sagittal alignment types observed on radiographs in young adults with thoracic hyperkyphosis. The relationship between cervical and thoracolumbar alignment as well as the effect of posterior instrumentation and adaptive positional changes of the mobile cervical segment were retrospectively analyzed.
  
  
  
  Twenty-three patients (32.7 years; 5-year follow-up) were included. Full spine radiographic measurements were: T1 slope, T1-T4 kyphosis, T4-T12 kyphosis, L1-S1 lordosis, pelvic incidence, pelvic tilt, sacral slope, SVA C7, SVA C2, lordosis between C0-C2, C2-C7, C2-C4 and C4-C7. A Bayesian model and Spearman correlation were used.
  
  
  
  Two alignment types existed: cervical lordosis (group A) and cervical kyphosis (group B). Preoperatively, T4-T12 kyphosis and L1-S1 lordosis were significantly higher in group A: 76.6° versus 59.4° and -72.8° versus -65.8° (probability of>5° difference P (β>5)>0.95). Pelvic incidence was higher in group A (49.8° versus 44.2°) and C0-C2 lordosis in group B (-29.4° versus -21.6°). A significant correlation existed between: T4-T12 kyphosis and C2-C7 lordosis, L1-S1 lordosis and pelvic incidence, C2-C7 lordosis and T1 slope, C2-C7 lordosis and T1-T4 kyphosis. Postoperatively, T4-T12 kyphosis decreased by 33.1° P (β>5)=0.9995), L1-S1 lordosis decreased by 17.7° (P (β>5)=0.961), T1-T4 kyphosis increased by 14.1° (P (β>5)=0.973). SVA C2 (translation) increased by 13.8mm. C0-C2 lordosis (head rotation) remained unchanged. Six patients changed cervical alignment. PJK occurred in 15 patients, unrelated to cervical alignment or proximal instrumentation level.
  
  
  
  Two cervical alignment types, lordotic or kyphotic, were observed thoracic hyperkyphosis patients. This alignment was mainly triggered by the amount of thoracic kyphosis and lumbar lordosis, linked to pelvic incidence. Moreover, the inclination of the C7-T1 junctional area plays a key role in the amount of cervical lordosis. The correction of T4-T12 kyphosis induced compensatory modifications at adjacent segments: T1-T4 kyphosis increase (PJK) and L1-S1 lordosis decrease. Global spino-pelvic alignment and head position did not change in the sagittal plane. The cervical spine tented to keep in its preoperative position in most patients.
  
  
  
  Level IV.
authors.affiliation: Service de chirurgie du rachis, fédération de médecine translationnelle (FMTS), université de Strasbourg, hôpitaux universitaires de Strasbourg, 1, place de l'Hôpital, BP 426, 67091 Strasbourg cedex, France.
authors.forename: F
authors.initials: F
authors.lastname: Paternostre
authors.affiliation: Service de chirurgie du rachis, fédération de médecine translationnelle (FMTS), université de Strasbourg, hôpitaux universitaires de Strasbourg, 1, place de l'Hôpital, BP 426, 67091 Strasbourg cedex, France. Electronic address: yann.philippe.charles@chru-strasbourg.fr.
authors.forename: Y P
authors.initials: YP
authors.lastname: Charles
authors.affiliation: Service de santé publique, fédération de médecine translationnelle (FMTS), université de Strasbourg, hôpitaux universitaires de Strasbourg, 1, place de l'Hôpital, BP 426, 67091 Strasbourg, France.
authors.forename: E A
authors.initials: EA
authors.lastname: Sauleau
authors.affiliation: Service de chirurgie du rachis, fédération de médecine translationnelle (FMTS), université de Strasbourg, hôpitaux universitaires de Strasbourg, 1, place de l'Hôpital, BP 426, 67091 Strasbourg cedex, France.
authors.forename: J-P
authors.initials: JP
authors.lastname: Steib
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007738:Kyphosis / Q000000981:diagnostic imaging / Q000601:surgery*; D008141:Lordosis / Q000000981:diagnostic imaging / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging; D008297:Male; D010384:Pelvic Bones / Q000000981:diagnostic imaging; D011184:Postoperative Period; D011187:Posture; D011859:Radiography; D016059:Range of Motion, Articular; D012189:Retrospective Studies; D012447:Sacrum / Q000000981:diagnostic imaging; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D055815:Young Adult
keywords: Adaptive positional changes; Cervical sagittal alignment; Proximal junctional kyphosis; Thoracic hyperkyphosis; Thoracolumbar alignment