title: [Sagittal balance and compensatory mechanism after segmental instrumentation for adolescent idiopathic scoliosis].
abstract: OBJECTIVE
  Previous studies have demonstrated good ability to improve the sagittal profile with the use of segmental instrumentation for adolescent idiopathic scoliosis (AIS) by analysing the sagittal vertical axis (SVA). However, several authors recommend analysing the spinopelvic relation in addition to the SVA. While compensatory mechanisms may neutralise a positive SVA, these mechanisms are energy consuming and may lead to unphysiological biomechanics, which can negatively influence the quality of life. The purpose of this radiographic analysis was to analyse global sagittal balance and to identify potential compensatory mechanisms after segmental instrumentation for AIS.
  
  
  METHODS
  From a prospectively collected multicentre database, patients with segmental instrumentation for AIS and a minimum follow-up of 2 years were identified. An additional inclusion criterion was the ability to measure lumbar lordosis (LL), pelvic tilt (PT), pelvic incidence (PI), and SVA on each X-ray (preoperative, 1st erect, and the 2-year follow-up visits). LL was analysed in relation to PI in order to identify iatrogenic changes. Changes in LL were correlated to changes in PT and SVA.
  
  
  RESULTS
  91 patients were included. On the 1st erect X-ray, LL significantly decreased from pre-op but the SVA remained stable due to a significant increase of PT. At two years follow-up, PT recurred to preoperative values, accompanied by a significant increase of SVA despite a compensatory hyperlordosis below the instrumentation. The temporary increase of PT on the 1st erect was significantly correlated to an iatrogenic decrease of LL. An iatrogenic decrease of LL was significantly correlated to an increase of SVA on the 1st erect and at 2 years follow-up.
  
  
  CONCLUSIONS
  An iatrogenic decrease of LL after segmental instrumentation for AIS is initially compensated for by pelvic retroversion and later by a hyperlordosis below the instrumentation.
authors.affiliation: Abteilung für Orthopädie, Otto-von-Guericke-Universität, 39120 Magdeburg. pertrobisch@gmail.com
authors.forename: P D
authors.initials: PD
authors.lastname: Trobisch
authors.forename: A F
authors.initials: AF
authors.lastname: Samdani
authors.forename: R
authors.initials: R
authors.lastname: Betz
authors.forename: J
authors.initials: J
authors.lastname: Pahys
authors.forename: P
authors.initials: P
authors.lastname: Cahill
mesh_terms: D000293:Adolescent; D005260:Female; D005500:Follow-Up Studies; D005858:Germany; D006801:Humans; D016268:Internal Fixators; D008297:Male; D011857:Radiographic Image Interpretation, Computer-Assisted; D015203:Reproducibility of Results; D012544:Scheuermann Disease / Q000000981:diagnostic imaging* / Q000601:surgery*; D012680:Sensitivity and Specificity; D016896:Treatment Outcome