Psychometric Properties of the Modified Japanese Orthopaedic Association Scale in Patients With Cervical Spondylotic Myelopathy

Study Design. Prospective study. Objective. This study aims to determine the psychometric properties of the modified Japanese Orthopaedic Association (mJOA) scale. Summary of Background Data. Several outcome measures assess functional impairment and quality of life in patients with cervical myelopathy. However, a "gold standard" has not been established. One of the most widely accepted tools for assessing functional status is the mJOA scale. Methods. Two hundred and seventy-seven surgical patients with cervical spondylotic myelopathy were enrolled in the prospective cervical spondylotic myelopathy-North America study. Functional status was evaluated at baseline and at 6, 12, and 24 months postoperatively. The internal consistency of the mJOA was assessed by computing a Cronbach a for the total score and after removing 1 item at a time. Convergent validity and divergent validity were measured by correlating the mJOA with other assessment tools. The responsiveness of the scale was determined by comparing mJOA scores at baseline and 12 months after surgery and computing a Cohen effect size. Results. The internal consistency of the scale was moderate with a Cronbach a of 0.63. Sphincter dysfunction measured a different dimension than the other 3 scale components. The mJOA was correlated with the Nurick score (r = -0.625) but was not associated with subscales of the Short-Form 36 that measure different constructs. These findings suggest convergent and divergent validity. The mJOA was responsive to change as reflected by a Cohen effect size of 1. Conclusion. The mJOA is a useful tool in the assessment of cervical spondylotic myelopathy and it should be adopted as the standard for evaluating functional status in this population.