人工股関節患者における日本語版Western Ontario and McMaster Universities Osteoarthritis Index(WOMAC)の信頼性と妥当性の検討

The Reliability and Validity of the Japanese Version of the Western Ontario and McMaster Universities Osteoarthritis Index(WOMAC)for Patients with Total Hip Arthroplasty

要旨

　本研究の目的は，人工股関節患者における主観的な身体的健康状態の測定するために，Western Ontario and McMaster Universities Osteoarthritis Index（WOMAC）（日本語翻訳版）の信頼性・妥当性を検討することである．術後1年以上の220名を分析した結果，WOMAC下位項目の「痛み」項目で床効果があったが，内的整合性はWOMACの3つの下位尺度内でのCronbach's α係数が0.74～0.95で，29名の再調査によるSpearman相関係数，各項目の一致率が高く，信頼性が示された．SF-36との比較による基準関連妥当性と弁別的妥当性は認められたが，構成妥当性についてはWOMAC（英語原版）と尺度構造が異なる股関節術後患者の身体的な特徴に即した4因子構造の解釈が妥当と考える．日本人股関節術患者において，WOMAC（日本語翻訳版）の信頼性・妥当性が示され，評価指標として有用なことが示唆された．

Abstract

　Purpose: The purpose of this study is to assess the reliability and validity of the Japanese version of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) for Japanese total hip arthroplasty (THA) patients.

　Methods: The WOMAC is a health related quality of life scale, comprised of three subscales, pain, stiffness, and physical function. Higher scores indicate stronger pain and higher degree of difficulty in functioning day to day activities. The questionnaire was mailed to 319 patients who underwent primary THA. Two scales were used including the Medical Outcomes Study 36-Item Short Form Health Survey (SF-36) Japanese Edition and the WOMAC. Thirty patients were randomly chosen for a test-retest reliability study 3 weeks after the initial survey.

　Results: Two-hundred and twenty questionnaires were analyzed. Although WOMAC pain had a floor effect, WOMAC subscale items showed good internal consistency (α=0.74~0.95), with intraclass correlations ranging from 0.45 to 0.71. Agreement rates between the two tests were high, and so were Spearman's rank correlations. Factor compositions were slightly different from the original study, which seems to reflect the influence of Japanese lifestyle and the specific physical function of the THA patients.

　Conclusion: These findings suggest that WOMAC is a reliable and valid measure for THA patients in Japan. Further research is needed to conduct a prospective study to follow up patients with OA from the pre-operative to the post-operative period using WOMAC to determine the validity of our findings.