Measuring illness beliefs in patients with lower extremity injuries: Reliability and validity of the Dutch version of the Somatic Pre-Occupation and Coping questionnaire (SPOC-NL)

INTRODUCTION: Positive coping strategies, illness perceptions and recovery expectations are associated with better clinical outcomes and earlier return to work after injuries. The Somatic Pre-Occupation and Coping (SPOC) questionnaire captures illness beliefs and coping towards recovery of physical function and return to work after surgical treatment of tibial shaft fractures. The aim of this study was to translate and culturally adapt the SPOC into Dutch (SPOC-NL) and evaluate its reliability and validity in patients with lower extremity injuries. MATERIALS: The SPOC-NL contains four subscales: Somatic complaints, Coping, Energy, and Optimism. Patients treated for lower extremity injuries (N=106) completed the SPOC-NL, Short Form-36 and Short Musculoskeletal Function Assessment (SMFA-NL) questionnaire, and reported their current work status and self-perceived work ability. To assess test-retest reliability, 56 patients completed the SPOC-NL for a second time two weeks after the first administration of the SPOC-NL. We calculated Cronbach's Alpha, intraclass correlation coefficients (ICCs) and G coefficients to measure internal consistency and overall reliability, and used the Bland and Altman method to assess bias between test and retest SPOC-NL scores. To determine construct validity, we explored 16 a priori hypotheses regarding correlations between SPOC-NL scores and subscale scores and SF-36, SMFA-NL, work status and work ability. RESULTS: Internal consistency was good to excellent, with Cronbach's Alpha values ranging between 0.79 and 0.94 and G coefficients ranging between 0.77 and 0.95. Test-retest reliability was also good, since high ICCs (0.72-0.91) and G coefficients (0.82-0.94) were found. Construct validity of the SPOC-NL was good, as 75% of the predefined hypotheses were confirmed. Compared to participants who were on sick leave or receiving disability benefits, participants with a paid job had significantly higher scores on the total score and the subscales Somatic complaints and Energy of the SPOC-NL. Participants with high work ability also had significantly higher scores on the total score and all subscales than participants with low work ability. DISCUSSION AND CONCLUSIONS: The SPOC-NL is a reliable and valid measure for the assessment of illness beliefs and coping towards recovery and it is strongly related to work status and self-perceived ability to work in patients with lower extremity injuries.