The Minimum Clinically Important Difference of the Modified Japanese Orthopaedic Association Scale in Patients with Degenerative Cervical Myelopathy

Study Design. Analysis of the prospective AOSpine CSM-International and North America datasets and survey of AO Spine International. Objective. This study aims to define the minimum clinically important difference (MCID) of the modified Japanese Orthopaedic Association (mJOA) in patients with degenerative cervical myelopathy (DCM). Summary of Background Data. The mJOA is the most frequently used clinician-administered tool to assess functional status in patients with DCM. By defining its MCID, clinicians can better evaluate treatment outcomes for this condition. Methods. Three methods were used to determine the MCID of the mJOA: (1) distribution-based, (2) anchor-based and receiver operating characteristic (ROC) analysis, and (3) professional opinion. Distribution-based methods were used to estimate the MCID by computing the half standard deviation and standard error of measurement. Using anchor-based methods, mJOA at 12 months after surgery was compared between patients who were slightly improved'' on the Neck Disability Index (NDI) and those who were unchanged.'' ROC analysis was performed to compute a discrete integer value for the MCID that yielded the smallest difference between sensitivity and specificity. We repeated anchor-based methods for patients with mild (mJOA: 15-17), moderate (mJOA: 12-14), and severe disease (mJOA < 12). Results. The half standard deviation of the baseline mJOA was 1.36 and the standard error of measurement was 1.21. The difference in mJOA between patients who slightly improved'' on the NDI and unchanged'' patients was 1.11. ROC analysis yielded a value of 2 for the MCID. The survey of 416 spine professionals confirmed these estimates: the mean response was 1.65 +/- 0.66. The MCID significantly varied depending on myelopathy severity: ROC analysis yielded a threshold of 1 for mild, 2 for moderate, and 3 for severe patients. Conclusion. The MCID of the mJOA is estimated to be between 1 and 2 points and varies with myelopathy severity. This knowledge will enable clinicians to identify meaningful functional improvements in DCM patients.