Translation, Cross-Cultural Adaptation and Psychometric Properties of the Persian Version of Patient-Specific Functional Scale in Patients with Chronic Low Back Pain.

Objectives: The major emphasis of physical therapy in patient evaluation is the assessment of physical function, and the Patient-Specific Functional Scale (PSFS) is one of the most commonly used instruments for this purpose. Therefore, the present study aims to translate and cross-culturally adapt the PSFS into Persian and test its psychometric properties in patients with chronic low back pain (CLBP).

Methods: The PSFS was translated from English to Persian and cross-culturally adapted in accordance with the study by Beaton et al. Psychometric properties of 100 CLBP patients were assessed. Reliability (internal consistency and test-retest) was examined for 32 participants who completed the Persian version of the PSFS (PSFS-P) twice with one week interval. Construct validity was assessed against the Persian versions of the Oswestry Disability Index (ODI-P) and the Numerical Pain Rating Scale (NPRS-P).

Results: The PSFS-P showed excellent reliability (Cronbach's alpha=0.88, intraclass correlation coefficient [ICC _{3, 1}] =0.95, 95% CI [0.87 to 0.98]). The construct validity analysis revealed a moderate negative correlation between PSFS-P and NPRS-P (r=-0.47) and a high negative correlation between PSFS-P and ODI-P (r=-0.61). The PSFS-P showed no floor and ceiling effects.

Conclusion: The PSFS-P has adequate psychometric properties and is applicable in both clinical settings and research involving the Iranian population with CLBP.