Japanese Orthopaedic Association Cervical Myelopathy Evaluation Questionnaire as an outcome measure for ossification of posterior longitudinal ligament patients in East Asia: an investigation of reliability, validity, and responsiveness

BACKGROUND: The surgical outcomes of individual patient with ossification of the posterior longitudinal ligament (OPLL) can vary depending on various patient-related factors. Japanese Orthopaedic Association Cervical Myelopathy Evaluation Questionnaire (JOACMEQ) is a well-developed tool for outcome measurement and considers both disease-specific and general health aspects. This study aimed to investigate the reliability, validity, and responsiveness of the JOACMEQ in patients with OPLL in mainland China and to compare post-operative outcomes of OPLL patients between mainland China and Japan. METHODS: This multicenter trial was performed between July 2009 and June 2019. The procedure for the JOACMEQ translation followed Beaton’s guidelines. All patients enrolled were diagnosed with OPLL and had completed the JOACMEQ, the modified Japanese Orthopaedic Association (mJOA) scale, and the 36-Item Short Form Health Survey (SF-36) before and after surgery. The reliability (Cronbach’s α and Pearson’s correlation), construct validity (factor analysis), concurrent validity (Spearman’s correlation with SF-36) and responsiveness (effect sizes) of JOACMEQ were evaluated. A mixed-model analytic approach was used to analyze differences in postoperative outcomes between the 2 countries. RESULTS: Ninety-one patients from mainland China and ninety-one patients from Japan were recruited. JOACMEQ showed satisfactory internal consistency (Cronbach’s α=0.75). In test-retest reliability evaluation, except for the bladder function domain, the JOACMEQ domains had good test-retest reliability (0.89–0.96). In factor analysis, most of the items (19/24) were well clustered. Regarding clinical validity, all 5 domains were found to have moderate correlations with the physical component summary (PCS) of SF-36 (r=0.25–0.50), and the bladder function and quality of life domains also had moderate correlations (r=0.25–0.50) with the mental component summary (MCS) of SF-36. JOACMEQ showed a variable responsiveness in different domains (effect size =0.17–0.84; standardized response means =0.15–0.85). Regarding postoperative improvements in the JOACMEQ score, mixed-model analysis revealed a significant difference in the quality of life domain between Chinese and Japanese patients (16.0±18.7 vs. 7.8±17.7, P<0.05). CONCLUSIONS: JOACMEQ generally shows good reliability, good validity and mild responsiveness, and can identify the post-operative improvements in patients with OPLL in mainland China. Chinese OPLL patients showed a significantly larger improvement in postoperative quality of life compared to their Japanese counterparts.