Thai version of the Marx Activity Rating Scale: Cross-cultural adaptation and validation in patients with anterior cruciate ligament injury

Abstract

Introduction/objectives: The Marx Activity Rating Scale (MARS) is a validated patient-reported outcome measure quantifying high-demand knee activity frequency in anterior cruciate ligament (ACL)–injured populations. The instrument consists of 4 domains: running, cutting, decelerating, and pivoting. This prospective validation study aimed to translate and cross-culturally adapt the MARS into Thai and evaluate its psychometric properties among ACL-injured patients. Methods: Cross-cultural adaptation followed Beaton's established guidelines, including translation, synthesis, backward translation, expert committee review, and pretesting. Validation of the Thai version of the MARS used dual recall timeframes: MARS with a 1-year recall period (MARS<inf>yr</inf>) and MARS with a 1-month recall period (MARS<inf>mo</inf>). A total of 110 ACL-injured patients, aged 18–50 years with pre-injury Tegner Activity Scale (TAS) scores ≥4, completed questionnaires at the baseline and 2-week follow-up. Psychometric evaluation encompassed construct validity, internal consistency, test-retest reliability, measurement error, and floor/ceiling effects. Results: Cross-cultural adaptation of the Thai version of the MARS was successfully completed. Construct validity of the instrument was demonstrated by correlations between the MARS and the TAS with corresponding timeframes (Spearman's correlation coefficient of 0.51–0.61). Internal consistency was excellent with Cronbach's α coefficients of 0.87 (MARS<inf>yr</inf>) and 0.93 (MARS<inf>mo</inf>). Test-retest reliability showed excellent intraclass correlation coefficients of 0.93 (MARS<inf>yr</inf>) and 0.94 (MARS<inf>mo</inf>). Notable floor effects (33.6% for MARS<inf>mo</inf>) and ceiling effects (26.4% for MARS<inf>yr</inf>) were observed. Conclusion: The MARS was successfully cross-culturally adapted into the Thai version. It exhibits acceptable psychometric properties for quantifying physical activity in ACL-injured populations. Floor/ceiling effects necessitate complementary outcome measures for comprehensive functional assessment. Level of evidence: II.