title: Role of pelvic translation and lower-extremity compensation to maintain gravity line position in spinal deformity.
abstract: OBJECTIVE
  Previous forceplate studies analyzing the impact of sagittal-plane spinal deformity on pelvic parameters have demonstrated the compensatory mechanisms of pelvis translation in addition to rotation. However, the mechanisms recruited for this pelvic rotation were not assessed. This study aims to analyze the relationship between spinopelvic and lower-extremity parameters and clarify the role of pelvic translation.
  
  
  METHODS
  This is a retrospective study of patients with spinal deformity and full-body EOS images. Patients with only stenosis or low-back pain were excluded. Patients were grouped according to T-1 spinopelvic inclination (T1SPi): sagittal forward (forward, > 0.5°), neutral (-6.3° to 0.5°), or backward (< -6.3°). Pelvic translation was quantified by pelvic shift (sagittal offset between the posterosuperior corner of the sacrum and anterior cortex of the distal tibia), hip extension was measured using the sacrofemoral angle (SFA; the angle formed by the middle of the sacral endplate and the bicoxofemoral axis and the line between the bicoxofemoral axis and the femoral axis), and chin-brow vertical angle (CBVA). Univariate and multivariate analyses were used to compare the parameters and correlation with the Oswestry Disability Index (ODI).
  
  
  RESULTS
  In total, 336 patients (71% female; mean age 57 years; mean body mass index 27 kg/m(2)) had mean T1SPi values of -8.8°, -3.5°, and 5.9° in the backward, neutral, and forward groups, respectively. There were significant differences in the lower-extremity and spinopelvic parameters between T1SPi groups. The backward group had a normal lumbar lordosis (LL), negative SVA and pelvic shift, and the largest hip extension. Forward patients had a small LL and an increased SVA, with a large pelvic shift creating compensatory knee flexion. Significant correlations existed between lower-limb parameter and pelvic shift, pelvic tilt, T-1 pelvic angle, T1SPi, and sagittal vertical axis (0.3 < r < 0.8; p < 0.001). ODI was significantly correlated with knee flexion and pelvic shift.
  
  
  CONCLUSIONS
  This is the first study to describe full-body alignment in a large population of patients with spinal pathologies. Furthermore, patients categorized based on T1SPi were found to have significant differences in the pelvic shift and lower-limb compensatory mechanisms. Correlations between lower-limb angles, pelvic shift, and ODI were identified. These differences in compensatory mechanisms should be considered when evaluating and planning surgical intervention for adult patients with spinal deformity.
authors.affiliation: Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, New York;|Department of Orthopaedic Surgery, Robert Debre Hospital, Paris, France.
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Ferrero
authors.affiliation: Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, New York;
authors.forename: Barthelemy
authors.initials: B
authors.lastname: Liabaud
authors.affiliation: Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, New York;
authors.forename: Vincent
authors.initials: V
authors.lastname: Challier
authors.affiliation: Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, New York;
authors.forename: Renaud
authors.initials: R
authors.lastname: Lafage
authors.affiliation: Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, New York;
authors.forename: Bassel G
authors.initials: BG
authors.lastname: Diebo
authors.affiliation: Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, New York;
authors.forename: Shaleen
authors.initials: S
authors.lastname: Vira
authors.affiliation: Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, New York;
authors.forename: Shian
authors.initials: S
authors.lastname: Liu
authors.affiliation: Department of Orthopaedic Surgery, CHU Pellegrin, Bordeaux; and.
authors.forename: Jean Marc
authors.initials: JM
authors.lastname: Vital
authors.affiliation: Department of Orthopaedic Surgery, Robert Debre Hospital, Paris, France.
authors.forename: Brice
authors.initials: B
authors.lastname: Ilharreborde
authors.affiliation: Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, New York;
authors.forename: Themistocles S
authors.initials: TS
authors.lastname: Protopsaltis
authors.affiliation: Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, New York;
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Errico
authors.affiliation: Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, New York;
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Schwab
authors.affiliation: Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, New York;
authors.forename: Virginie
authors.initials: V
authors.lastname: Lafage
mesh_terms: D005260:Female; D006801:Humans; D035002:Lower Extremity / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010388:Pelvis / Q000000981:diagnostic imaging / Q000503:physiopathology*; D011187:Posture / Q000502:physiology*; D011857:Radiographic Image Interpretation, Computer-Assisted; D012189:Retrospective Studies; D012399:Rotation; D013121:Spinal Curvatures / Q000000981:diagnostic imaging / Q000503:physiopathology*; D051598:Whole Body Imaging
keywords: AA = ankle angle; ASD = adult spinal deformity; BMI = body mass index; C7PL = C-7 plumb line; CBVA = chin-brow vertical angle; GL = gravity line; KA = knee angle; LL = lumbar lordosis; ODI = Oswestry Disability Index; PI = pelvic incidence; PT = pelvic tilt; SFA = sacrofemoral angle; SS = sacral slope; SVA = sagittal vertical axis; T-1 spinopelvic inclination; T1SPi = T-1 spinopelvic inclination; T9SPi = T-9 spinopelvic inclination; TK = thoracic kyphosis; TPA = T-1 pelvic angle; compensatory mechanisms; full-body radiography; pelvic shift; pelvic tilt; sagittal alignment; spine deformity