title: Virtual Modeling of Postoperative Alignment After Adult Spinal Deformity Surgery Helps Predict Associations Between Compensatory Spinopelvic Alignment Changes, Overcorrection, and Proximal Junctional Kyphosis.
abstract: METHODS
  Retrospective review of a prospective multicenter database.
  
  
  OBJECTIVE
  To develop a method to analyze sagittal alignment, free of the influence of proximal junctional kyphosis (PJK), and then compare PJK to non-PJK patients using this method.
  
  
  BACKGROUND
  PJK after adult spinal deformity (ASD) surgery remains problematic as it alters sagittal alignment. The present study proposes a novel virtual modeling technique that attempts to eliminate the confounding effects of PJK on postoperative spinal alignment.
  
  
  METHODS
  A virtual spinal modeling technique was developed on a retrospective ASD cohort of patients with multilevel spinal fusions to the pelvis with at least 2-year postoperative follow-up. The virtual postoperative alignment (VIRTUAL) was created from the postoperative alignment of the instrumented segments and the preoperative alignment of the unfused segments. VIRTUAL was validated by comparisons to actual 2-year postoperative alignment (REAL) in non-PJK patients. Patients were then divided into two groups: PJK and non-PJK based on the presence/absence of PJK at 2 years postoperatively. PJK and non-PJK patients were compared using VIRTUAL and REAL.
  
  
  RESULTS
  A total of 458 patients (78F, mean 57.9 yr) were analyzed. The validation of VIRTUAL versus REAL demonstrated correlation coefficients greater than 0.7 for all measures except sagittal vertical axis (SVA; r = 0.604). At 2 years, REAL alignment in PJK patients demonstrated a smaller pelvic incidence minus lumbar lordosis and a larger thoracic kyphosis than non-PJK patients, but similar SVA, T1 pelvic angle, and pelvic tilt. An analysis of VIRTUAL demonstrated that patients with PJK had a smaller pelvic incidence minus lumbar lordosis, pelvic tilt, SVA, and T1 pelvic angle than non-PJK patients (P < 0.05).
  
  
  CONCLUSIONS
  This technique demonstrated strong correlations with actual postoperative alignment. Comparisons between REAL and VIRTUAL alignments revealed that postoperative PJK may develop partially as a compensatory mechanism to the overcorrection of sagittal deformities. Future research will evaluate the appropriate thresholds for deformity correction according to age and ASD severity.
  
  
  METHODS
  3.
authors.affiliation: Spine Service, Hospital for Special Surgery, New York, NY.
authors.forename: Renaud
authors.initials: R
authors.lastname: Lafage
authors.affiliation: Spine Division, Department of Orthopedics, NYU Langone Medical Center, New York, NY.
authors.forename: Shay
authors.initials: S
authors.lastname: Bess
authors.affiliation: Department of Orthopedic Surgery, University of Louisville Medical Center, Louisville, KY.
authors.forename: Steve
authors.initials: S
authors.lastname: Glassman
authors.affiliation: Department of Neurosurgery, San Francisco Medical Center, University of California, San Francisco, CA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Ames
authors.affiliation: Department of Orthopedic Surgery, University of Kansas Medical Center, Kansas City, KS.
authors.forename: Douglas
authors.initials: D
authors.lastname: Burton
authors.affiliation: Department of Orthopedic Surgery, Oregon Health Sciences University, Portland, OR.
authors.forename: Robert
authors.initials: R
authors.lastname: Hart
authors.affiliation: Spine Service, Hospital for Special Surgery, New York, NY.
authors.forename: Han J
authors.initials: HJ
authors.lastname: Kim
authors.affiliation: Department of Orthopedic Surgery, University of California, Davis, Sacramento, CA.
authors.forename: Eric
authors.initials: E
authors.lastname: Klineberg
authors.affiliation: Spine Division, Department of Orthopedics, NYU Langone Medical Center, New York, NY.
authors.forename: Jensen
authors.initials: J
authors.lastname: Henry
authors.affiliation: Rocky Mountain Hospital for Children Denver, Denver, CO.
authors.forename: Breton
authors.initials: B
authors.lastname: Line
authors.affiliation: Department of Neurological Surgery, Northwestern University Feinberg School of Medicine, Chicago, IL.
authors.forename: Justin
authors.initials: J
authors.lastname: Scheer
authors.affiliation: Spine Division, Department of Orthopedics, NYU Langone Medical Center, New York, NY.
authors.forename: Themistocles
authors.initials: T
authors.lastname: Protopsaltis
authors.affiliation: Spine Service, Hospital for Special Surgery, New York, NY.
authors.forename: Frank
authors.initials: F
authors.lastname: Schwab
authors.affiliation: Spine Service, Hospital for Special Surgery, New York, NY.
authors.forename: Virginie
authors.initials: V
authors.lastname: Lafage
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D000368:Aged; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007738:Kyphosis / Q000000981:diagnostic imaging* / Q000209:etiology; D008297:Male; D008875:Middle Aged; D008953:Models, Anatomic; D019635:Neurosurgical Procedures / Q000009:adverse effects / Q000639:trends; D010384:Pelvic Bones / Q000000981:diagnostic imaging*; D011183:Postoperative Complications / Q000000981:diagnostic imaging* / Q000209:etiology; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012189:Retrospective Studies; D013123:Spinal Fusion / Q000009:adverse effects / Q000639:trends*; D000076142:Virtual Reality