Cross-cultural adaptation, reliability and validity of the Turkish version of the Lower Limb Functional Index

This study aims to adapt culturally a Turkish version of the Lower Limb Functional Index (LLFI) and to determine its validity, reliability, internal consistency, measurement sensitivity and factor structure in lower limb problems.

The LLFI was translated into Turkish and cross-culturally adapted with a double forward-backward protocol that determined face and content validity. Individuals (n = 120) with lower limb musculoskeletal disorders completed the LLFI and Short Form-36 questionnaires and the Timed Up and Go physical test. The psychometric properties were evaluated for the all participants from patient-reported outcome measures made at baseline and repeated at day 3 to determine criterion between scores (Pearson's r), internal consistency (Cronbachs α) and test-retest reliability (intraclass correlation coefficient - ICC_2.1). Error was determined using standard error of the measurement (SEM) and minimal detectable change at the 90% level (MDC₉₀), while factor structure was determined using exploratory factor analysis with maximum likelihood extraction and Varimax rotation.

The psychometric characteristics showed strong criterion validity (r = 0.74-0.76), high internal consistency (α = 0.82) and high test-retest reability (ICC_2.1 = 0.97). The SEM of 3.2% gave an MDC₉₀ = 5.8%. The factor structure was uni-dimensional.

Turkish version of LLFI was found to be valid and reliable for the measurement of lower limb function in a Turkish population. Implications for Rehabilitation Lower extremity musculoskeletal disorders are common and greatly impact activities among the affected individuals pertaining to daily living, work, leisure and quality of life. Patient-reported outcome (PRO) measures have advantages as they are practical, cost-effective and clinically convenient for use in patient-centered care. The Lower Limb Functional Index is a recently validated PRO measure shown to have strong clinimetric properties.