Development and validation of risk stratification models for adult spinal deformity surgery

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  • 1 Spine Surgery Unit, Vall d’Hebron Hospital, Barcelona, Spain;
  • | 2 Center for Research in Health and Economics, Universitat Pompeu Fabra, Barcelona, Spain;
  • | 3 Department of Neurosurgery, University of Virginia Medical Center, Charlottesville, Virginia;
  • | 4 Department of Orthopaedic Surgery, Washington University, St. Louis, Missouri;
  • | 5 Spine Research Unit, Vall d’Hebron Institute of Research (VHIR), Barcelona, Spain;
  • | 6 Spine Surgery Unit, Hospital Universitario La Paz, Madrid, Spain;
  • | 7 Denver International Spine Center, Presbyterian St. Luke’s/Rocky Mountain Hospital for Children, Denver, Colorado;
  • | 8 Norton Leatherman Spine Center, Louisville, Kentucky;
  • | 9 Department of Orthopedic Surgery, University of Kansas Medical Center, Kansas City, Kansas;
  • | 10 Ankara ARTES Spine Center, Ankara, Turkey;
  • | 11 Spine Center Division, Department of Orthopedics and Neurosurgery, Schulthess Klinik, Zürich, Switzerland;
  • | 12 Department of Orthopedic Surgery, Hospital for Special Surgery, New York, New York;
  • | 13 Spine Surgery Unit, Bordeaux University Hospital, Bordeaux, France;
  • | 14 Department of Orthopedics and Traumatology, Acıbadem University, Istanbul, Turkey; and
  • | 15 Department of Neurosurgery, University of California, San Francisco, California
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Adult spinal deformity (ASD) surgery has a high rate of major complications (MCs). Public information about adverse outcomes is currently limited to registry average estimates. The object of this study was to assess the incidence of adverse events after ASD surgery, and to develop and validate a prognostic tool for the time-to-event risk of MC, hospital readmission (RA), and unplanned reoperation (RO).


Two models per outcome, created with a random survival forest algorithm, were trained in an 80% random split and tested in the remaining 20%. Two independent prospective multicenter ASD databases, originating from the European continent and the United States, were queried, merged, and analyzed. ASD patients surgically treated by 57 surgeons at 23 sites in 5 countries in the period from 2008 to 2016 were included in the analysis.


The final sample consisted of 1612 ASD patients: mean (standard deviation) age 56.7 (17.4) years, 76.6% women, 10.4 (4.3) fused vertebral levels, 55.1% of patients with pelvic fixation, 2047.9 observation-years. Kaplan-Meier estimates showed that 12.1% of patients had at least one MC at 10 days after surgery; 21.5%, at 90 days; and 36%, at 2 years. Discrimination, measured as the concordance statistic, was up to 71.7% (95% CI 68%–75%) in the development sample for the postoperative complications model. Surgical invasiveness, age, magnitude of deformity, and frailty were the strongest predictors of MCs. Individual cumulative risk estimates at 2 years ranged from 3.9% to 74.1% for MCs, from 3.17% to 44.2% for RAs, and from 2.67% to 51.9% for ROs.


The creation of accurate prognostic models for the occurrence and timing of MCs, RAs, and ROs following ASD surgery is possible. The presented variability in patient risk profiles alongside the discrimination and calibration of the models highlights the potential benefits of obtaining time-to-event risk estimates for patients and clinicians.


ACS NSQIP = American College of Surgeons National Surgical Quality Improvement Program; ASD = adult spinal deformity; EBL = estimated blood loss; LIV = lowest instrumented vertebra; MC = major complication; ODI = Oswestry Disability Index; OOB = out of bag; PROM = patient-reported outcome measure; RA = readmission; RO = reoperation; SF-36 = SF-36v2 Health Survey; SRS-22r = Scoliosis Research Society 22-item patient outcome questionnaire.

Supplementary Materials

    • Supplemental Tables and Figures (PDF 3.42 MB)

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