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

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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.

ABBREVIATIONS 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.

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Contributor Notes

Correspondence Ferran Pellisé: Hospital Vall d’Hebron, Barcelona, Spain. WHEN CITING Published online June 28, 2019; DOI: 10.3171/2019.3.SPINE181452.Disclosures The International Spine Study Group Foundation (ISSGF) receives funding support from DePuy Synthes, K2M, NuVasive, Orthofix, and Zimmer Biomet. The European Spine Study Group receives funding support from DePuy Synthes and Medtronic. Additional support was provided through Project PI16/01283, funded by Instituto de Salud Carlos III and cofunded by the European Union (ERDF/ESF). Dr. Pellisé is a consultant for DePuy Synthes Spine and received support from DePuy Synthes Spine and Medtronic for the study described. Dr. Smith is a consultant for K2M, AlloSource, Cerapedics, Zimmer Biomet, and NuVasive and receives fellowship funding from NREF and AOSPine, research funding from AOSpine, and royalties from Zimmer Biomet. Dr. Kelly receives support from DePuy Synthes for non–study-related effort. Dr. Pérez-Grueso received support from DePuy Synthes for the study described. Dr. Bess is a consultant for K2 and has received support from the ISSGF for the study described and non–study-related effort. Dr. Gum is an employee of Norton Healthcare; is a consultant for Medtronic, DePuy, Stryker, Acuity, K2M, PacMed, and NuVasive; received support from Intellirod, Integra, Pfizer, and ISSFG for the study described; has direct stock ownership in Cingulate Therapeutics; and receives royalties from Acuity. Dr. Burton holds a patent with and received support for the study described from DePuy and has received non–study-related support from AlloSource and Pfizer. Dr. Acaroğlu received support from DePuy Synthes and Medtronic for the study described. Dr. Kleinstück received support from DePuy Synthes for the study described. Dr. Lafage is a consultant for Globus, has speaking/teaching arrangements with DePuy Synthes Spine, AOSpine, and K2M, and receives support from DePuy Synthes Spine, NuVasive, K2M, and Stryker (the latter paid through ISSGF). Dr. Obeid is a consultant for Medtronic and DePuy Synthes, received support from DePuy Synthes for the study described, and holds patents with Spineart, Clariance, and Alphatec. Dr. Schwab is a consultant for Zimmer Biomet, Globus, Medicrea, MSD, and K2M; has speaking/teaching arrangements with Zimmer Biomet, Globus, MSD, and K2M; and receives support from DePuy Synthes Spine, NuVasive, K2M, and Stryker for non–study-related effort. Dr. Shaffrey is a consultant for Medtronic, NuVasive, and Zimmer Biomet; has stock ownership in NuVasive; and holds patents with Medtronic, NuVasive, and Zimmer Biomet. Dr. Ames is an employee of UCSF; is a consultant for DePuy Synthes, Medtronic, K2M, Stryker, Medicrea, and Zimmer Biomet; receives royalties from Stryker, Zimmer Biomet Spine, DePuy Synthes, NuVasive, Next Orthosurgical, K2M, and Medicrea; conducts research for Titan Spine, DePuy Synthes, and ISSGF; has received grant funding from SRS; serves on the executive committee of International Spine Study Group; and is the director of Global Spine Analytics.


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