Original ArticleConventional JOA score for cervical myelopathy has a rater's bias -In comparison with JOACMEQ-
Introduction
Many articles have been published annually on the surgical outcomes for cervical compression myelopathy. Although most of them reported excellent outcomes, the operative gain widely varied from small to large using the Japan Orthopaedic Association (JOA) score which has been the standard outcome measure for myelopathy in Japan [1]. For example, recovery rate varies from 40 to 70% [2], [3]. Recovery rate is figured out from JOA score as the operative gain points divided by the difference between preoperative score and full score (17) [4].
There are two possible causes for this wide variation in recovery rate in previous studies. Prognostic factors of operative candidates might be different. Patients with good prognostic factors would yield a large gain, while those with poor prognostic factors would make only small gains. Another possible cause is raters' bias in giving the JOA score, which is usually rated by a surgeon or other medical staff. Some raters might always give a larger or smaller JOA score than other raters do even for a patient of the same disability. It is impossible to remove this kind of bias from the JOA score evaluation. By itself or in combination, these two causes lead to the difference of operative gain in the JOA scores. Japanese Orthopaedic Association Cervical Myelopathy Evaluation Questionnaire (JOACMEQ) was recently established to minimize this kind of bias by using self-recording questionnaires [5].
In this study, disease severity, the most important prognostic factor, was equalized between patient groups by a special statistical method called inverse-probability weighting (IPW) [6]. It enabled us to ignore the inequality of patients and exclusively detect raters' biases, if any, in the JOA score.
Section snippets
Materials and methods
This study was approved by the institutional review board and informed consent was obtained from each patient. Operative candidates with cervical myelopathy in whom the preoperative JOA score, JOACMEQ and Visual Analog Scale (VAS) score were completely recorded were included in the study. There were 234 patients (male 161, female 73, age 65.9 ± 10.3 (35–86)) and the diseases were spondylotic myelopathy or disc herniation in 185 patients and the ossification of posterior longitudinal ligament in
Unadjusted data
The results of unadjusted analyses are shown in Table 1. Gray boxes indicate p value less than 0.05. There were significant differences between the four groups in upper extremity function, lower extremity function and Quality of Life (QOL) of JOACMEQ and VAS score of lower extremity.
Adjusted data –inter-group comparison–
After the adjustment for the adjusted 6 variables, averaged Cohen's d in each inter-group comparison was 1.3%–5.1% (Table 2). Values in the parenthesis represent those before the adjustment. All of them were less
Discussion
The JOA score was established in 1975 [1] and modified in 1994 [10]. It consists of several subscores including finger motor function, shoulder and elbow muscle strength, lower extremity motor, upper extremity sensory, trunk sensory, lower extremity sensory and bladder function. By choosing corresponding items in each subscore and summing up points allocated to each item, a rater can easily calculate JOA scores, though weighing of each item has no statistical basis. Furthermore, being expressed
Conflict of interest
The authors declare that they have no conflict of interest.
Acknowledgment
This study was presented at the 45th annual meeting of the Japanese society for spine surgery and related research, Tokyo, April 14th, 2016.
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