title: A clinical prediction model to assess surgical outcome in patients with cervical spondylotic myelopathy: internal and external validations using the prospective multicenter AOSpine North American and international datasets of 743 patients.
abstract: BACKGROUND
  Clinical prediction rules are valuable tools in a surgical setting but should not be used to guide clinical practice until validated in other populations.
  
  
  OBJECTIVE
  The objective of this study was to validate a clinical prediction rule developed to determine surgical outcome in patients with cervical spondylotic myelopathy (CSM). The study will also identify key clinical predictors of outcome at a global level.
  
  
  METHODS
  This is a prospective multicenter cohort study.
  
  
  METHODS
  Two-hundred seventy-eight and 479 surgical CSM patients enrolled in the AOSpine CSM-North American (CSM-NA) and CSM-International (CSM-I) studies, respectively.
  
  
  METHODS
  The outcome measure was a Modified Japanese Orthopedic Association (mJOA) Scale.
  
  
  METHODS
  A clinical prediction model was built using data from 272 patients enrolled in the CSM-NA study. Bootstrapping was used for internal validation. The original model was externally validated using data on 471 patients participating in the CSM-I study. The predictive performance of the model was evaluated, including its discrimination, measured by area under the receiver-operating curve (AUC), and calibration, assessed by calibration slope, observed:expected ratios, and Hosmer-Lemeshow goodness-of-fit test.
  
  
  RESULTS
  The modified original model consisted of six covariates: age (odds ratio [OR], 0.96), duration of symptoms (0.76), baseline severity score (1.21), psychiatric comorbidities (0.44), impairment of gait (2.48), and smoking status (0.50). The AUC for the original model was 0.77 (95% confidence interval [CI]: 0.71, 0.82) and across the bootstrap replicates was 0.77 (95% CI: 0.76, 0.77), reflecting good discrimination and internal validity. The model tested on the CSM-I dataset yielded an AUC of 0.74 (95% CI: 0.69, 0.79), a calibration slope of 0.75, and an insignificant Hosmer-Lemeshow test. The ORs generated for baseline mJOA (OR, 1.26), impairment of gait (2.67), age (0.97), and smoking (0.55) were very similar to the original values of 1.28, 2.39, and 0.97, respectively. Duration of symptoms (OR, 0.94) had a significantly different odds ratio than in the original model, but the direction of its relationship with outcome was the same. Psychiatric comorbidities was not a significant predictor at an international level, likely because of underreporting: only six patients outside of North American centers were diagnosed with depression or bipolar.
  
  
  CONCLUSIONS
  The parameter estimates generated from the original analysis were internally valid. The original model was also externally valid. The most significant global predictors of surgical outcome were baseline myelopathy severity, age, smoking status and impaired gait.
authors.affiliation: Toronto Western Hospital, University Health Network, University of Toronto, Rm 4F-412, 399 Bathurst St, Toronto, Ontario M5T2S8, Canada.
authors.forename: Lindsay A
authors.initials: LA
authors.lastname: Tetreault
authors.affiliation: Faculty of Health Sciences, University of Ontario Institute of Technology (UOIT), 2000 Simcoe Street North, Oshawa, ON L1H 7K4, Canada; Centre for the Study of Disability Prevention and Rehabilitation, Canadian Memorial Chiropractic College (CMCC), University of Ontario Institute of Technology (UOIT), 2000 Simcoe Street North, Oshawa, ON L1H 7K4, Canada.
authors.forename: Pierre
authors.initials: P
authors.lastname: Côté
authors.affiliation: Department of Health Services, University of Washington, 4333 Brooklyn Ave. NE, Ste 1400/#315, Box #359455, Seattle, WA 98195, USA.
authors.forename: Branko
authors.initials: B
authors.lastname: Kopjar
authors.affiliation: Department of Neurosurgery, University of Kansas, 3901 Rainbow Blvd, Kansas City, KS 66160, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Arnold
authors.affiliation: Toronto Western Hospital, University Health Network, University of Toronto, Rm 4F-412, 399 Bathurst St, Toronto, Ontario M5T2S8, Canada. Electronic address: Michael.Fehlings@uhn.on.ca.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Fehlings
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002574:Cervical Vertebrae / Q000473:pathology / Q000601:surgery*; D015331:Cohort Studies; D015897:Comorbidity; D003661:Decision Support Techniques; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D011446:Prospective Studies; D015203:Reproducibility of Results; D013118:Spinal Cord Diseases / Q000601:surgery*; D055009:Spondylosis / Q000601:surgery*; D016896:Treatment Outcome; D014481:United States
keywords: Calibration; Cervical spondylotic myelopathy; Clinical prediction rule; Discrimination; Duration of symptoms; External validation; Myelopathy severity; Predictors; Surgical outcome