title: Multicenter validation of a formula predicting postoperative spinopelvic alignment.
abstract: OBJECTIVE
  Sagittal spinopelvic imbalance is a major contributor to pain and disability for patients with adult spinal deformity (ASD). Preoperative planning is essential for pedicle subtraction osteotomy (PSO) candidates; however, current methods are often inaccurate because no formula to date predicts both postoperative sagittal balance and pelvic alignment. The authors of this study aimed to evaluate the accuracy of 2 novel formulas in predicting postoperative spinopelvic alignment after PSO.
  
  
  METHODS
  This study is a multicenter retrospective consecutive PSO case series. Adults with spinal deformity (> 21 years old) who were treated with a single-level lumbar PSO for sagittal imbalance were evaluated. All patients underwent preoperative and a minimum of 6-month postoperative radiography. Two novel formulas were used to predict the postoperative spinopelvic alignment. The results predicted by the formulas were then compared with the actual postoperative radiographic values, and the formulas' ability to identify successful (sagittal vertical axis [SVA] ≤ 50 mm and pelvic tilt [PT] ≤ 25°) and unsuccessful (SVA > 50 mm or PT > 25°) outcomes was evaluated.
  
  
  RESULTS
  Ninety-nine patients met inclusion criteria. The median absolute error between the predicted and actual PT was 4.1° (interquartile range 2.0°-6.4°). The median absolute error between the predicted and actual SVA was 27 mm (interquartile range 11-47 mm). Forty-one of 54 patients with a formula that predicted a successful outcome had a successful outcome as shown by radiography (positive predictive value = 0.76). Forty-four of 45 patients with a formula that predicted an unsuccessful outcome had an unsuccessful outcome as shown by radiography (negative predictive value = 0.98).
  
  
  CONCLUSIONS
  The spinopelvic alignment formulas were accurate when predicting unsuccessful outcomes but less reliable when predicting successful outcomes. The preoperative surgical plan should be altered if an unsuccessful result is predicted. However, even after obtaining a predicted successful outcome, surgeons should ensure that the predicted values are not too close to unsuccessful values and should identify other variables that may affect alignment. In the near future, it is anticipated that the use of these formulas will lead to better surgical planning and improved outcomes for patients with complex ASD.
authors.affiliation: Department of Orthopedic Surgery, New York University Langone Medical Center-Hospital for Joint Diseases, New York, New York, USA. virginie.lafage@gmail.com
authors.forename: Virginie
authors.initials: V
authors.lastname: Lafage
authors.forename: Neil J
authors.initials: NJ
authors.lastname: Bharucha
authors.forename: Frank
authors.initials: F
authors.lastname: Schwab
authors.forename: Robert A
authors.initials: RA
authors.lastname: Hart
authors.forename: Douglas
authors.initials: D
authors.lastname: Burton
authors.forename: Oheneba
authors.initials: O
authors.lastname: Boachie-Adjei
authors.forename: Justin S
authors.initials: JS
authors.lastname: Smith
authors.forename: Richard
authors.initials: R
authors.lastname: Hostin
authors.forename: Christopher
authors.initials: C
authors.lastname: Shaffrey
authors.forename: Munish
authors.initials: M
authors.lastname: Gupta
authors.forename: Behrooz A
authors.initials: BA
authors.lastname: Akbarnia
authors.forename: Shay
authors.initials: S
authors.lastname: Bess
mesh_terms: D000328:Adult; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D007738:Kyphosis / Q000000981:diagnostic imaging / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D010027:Osteotomy; D010388:Pelvis / Q000000981:diagnostic imaging / Q000601:surgery*; D011237:Predictive Value of Tests; D011859:Radiography; D012189:Retrospective Studies; D012600:Scoliosis / Q000000981:diagnostic imaging / Q000601:surgery*; D013123:Spinal Fusion; D013131:Spine / Q000000981:diagnostic imaging / Q000601:surgery*; D016896:Treatment Outcome