Functional outcome instruments used for cervical spondylotic myelopathy: interscale correlation and prediction of preference-based quality of life

Background contextThere is limited literature comparing different functional outcome measures used for cervical spondylotic myelopathy (CSM).PurposeTo determine the correlation among five functional outcome measures used in CSM patient assessment and their ability to predict preference-based quality of life (QOL).Study design/settingProspective observational study.Patient samplePatients, aged 40 to 85 years, with CSM and cervical spinal cord compression at two or more levels from degenerative spondylosis were enrolled from seven sites over a 2-year period.Outcome measuresThe modified Japanese Orthopedic Association scale, Oswestry neck disability index (Oswestry NDI or Oswestry), Nurick scale, norm-based short-form 36 physical component summary, and EuroQol-5D (EQ-5D) were collected.MethodsThe Jean and David Wallace foundation provided funding for this study. Cervical spondylotic myelopathy patients undergoing either anterior or posterior surgery were prospectively followed with five different functional outcome measures over 1 year. Correlations among scales were tested using the Spearman rank correlation test. The sensitivity and specificity of each scale for predicting the global index of the EQ-5D were determined, and receiver-operating characteristic analysis was used to compare each scale's ability to discriminate QOL.ResultsA total of 106 patients were initially enrolled; 103 were operated on for CSM and followed for 1 year. Their ages ranged from 40 to 82 years (mean 61.9), and 61.3% were men. Correlations among the various functional outcome instruments were all highly significant (p<.001), but the degree of correlation varied greatly. Correlation between the EQ-5D scale and the Nurick scale was the least (Spearman rho 0.5539); correlation was the highest with the Oswestry NDI (Spearman rho 0.8306). The Oswestry NDI also had the greatest ability to discriminate favorable from adverse QOL compared with the other outcome instruments (p=.023).ConclusionsPreference-based quality-of-life instruments, such as the EQ-5D, are important measures for studying spinal disorders. Among the various commonly used outcome instruments for CSM, the Oswestry NDI is the most predictive of preference-based QOL.