This study aimed to perform linguistic and cross-cultural adaptation to establish a Polish version of the Lower Limb Functional Index (LLFI) as well as an evaluation of the psychometric properties. This was a two-stage, cross-sectional study. The first stage—linguistic and cultural adaptation, complied with the International Society for Pharmacoeconomics and Outcomes Research guidelines to produce the Lower Limb Functional Index, Polish version (LLFI-PL). The subjects were recruited to the second stage of the study from a sample of convenience (n = 125, age x- = 52.86 ± 19.53 years, 56% female, symptoms duration x- = 17.69 ± 18.39 weeks). Baseline reliability was performed on the LLFI-PL with retest period at 3–7 days. The Western Ontario and McMaster University Osteoarthritis Index (WOMAC), EuroQol Health Questionnaire 5-Dimensions 5-Level (EQ-5D-5L), and an 11-point Pain Numerical Rating Scale (P-NRS) were completed to assess the validity of the LLFI-PL. Statistical analysis showed high internal consistency (α = 0.94), and excellent test–retest reliability (ICC2.1 = 0.96). The measurement error was SEM = 1.69% with MDC90 = 3.93%. Construct validity demonstrated strong correlations between the LLFI-PL and WOMAC (r = 0.81) and moderate correlations with the EQ-5D-5L (r = −0.63) and P-NRS (r = −0.39). Exploratory factor analysis confirmed a single-factor structure. The LLFI-PL is a psychometrically sound questionnaire for Polish-speaking patients with lower limb musculoskeletal conditions. The results support findings from the previous original English, Spanish, and Turkish versions.

Background: Patient reported outcome measures (PROMs) are recommended to enable the standardization of collected data and provide accurate representation of the patients’ subjective opinions of their functional capabilities. The purpose of this study was to perform linguistic and cross-cultural adaptation to establish a Polish version of the Lower Limb Functional Index (LLFI), and to evaluate the psychometric properties of internal consistency, reliability, error score, validity, and factor structure with standardized criteria PROMs in a population with lower limb problems. Methods: Linguistic and cultural adaptation complied with the International Society for Pharmacoeconomics and Outcomes Research (ISPOR) guidelines to produce the Lower Limb Functional Index-Polish version (LLFI-PL). The study recruited subjects (n=125, age =52.86±19.53 years, range 20-87, 56% female, injury duration =17.69±18.39 weeks, range 5-71). Baseline reliability and criterion validity included the LLFI-PL, Western Ontario and McMaster University Osteoarthritis Index (WOMAC), Euroqol Health Questionnaire 5-Dimensions (EQ-5D-5L), and an 11-point pain Numerical Rating Scale, with retest at 3-7 days. Practicality for readability was considered within the face and content validity. Completion and scoring time were also calculated. Results: Statistical analysis showed excellent internal consistency ( α =0.94) and high test-retest reliability (ICC=0.96). The error score found the SEM=3.49% with MDC 90 =8.11%. Validity analysis showed strong correlations between the LLFI-PL with the WOMAC (r=-0.81) and moderate with the EQ-5D-5L (r=-0.63). Exploratory factor analysis confirmed a single-factor structure. Times for completion (172±33 seconds) and scoring (20±9 seconds) were determined. Conclusions: The LLFI-PL is a psychometrically sound questionnaire for Polish-speaking patients with lower limb musculoskeletal conditions. The results support the findings of previous original-English, Spanish, and Turkish versions for internal consistency, validity, reliability, error score, and factor structure.

Background: Patient reported outcome measures (PROMs) are recommended to enable the standardization of collected data and provide accurate representation of the patients’ subjective opinions of their functional capabilities. The purpose of this study was to perform linguistic and cross-cultural adaptation to establish a Polish version of the Lower Limb Functional Index (LLFI), and to evaluate the psychometric properties of internal consistency, reliability, error score, validity, and factor structure with standardized criteria PROMs in a population with lower limb problems.Methods: Linguistic and cultural adaptation complied with the International Society for Pharmacoeconomics and Outcomes Research (ISPOR) guidelines to produce the Lower Limb Functional Index - Polish version (LLFI-PL). The study recruited subjects (n = 125, age = 52.86 ± 19.53 years, range 20–87, 56% female, injury duration = 17.69 ± 18.39 weeks, range 5–71). Baseline reliability and criterion validity included the LLFI-PL, Western Ontario and McMaster University Osteoarthritis Index (WOMAC), Euroqol Health Questionnaire 5-Dimensions (EQ-5D-5L), and an 11-point pain Numerical Rating Scale, with retest at 3–7 days. Practicality for readability was considered within the face and content validity. Completion and scoring time were also calculated.Results: Statistical analysis showed excellent internal consistency (α = 0.94) and high test-retest reliability (ICC = 0.96). The error score found the SEM = 3.49% with MDC90 = 8.11%. Validity analysis showed strong correlations between the LLFI-PL with the WOMAC (r=-0.81) and moderate with the EQ-5D-5L (r=-0.63). Exploratory factor analysis confirmed a single-factor structure. Times for completion (172 ± 33 seconds) and scoring (20 ± 9 seconds) were determined.Conclusions: The LLFI-PL is a psychometrically sound questionnaire for Polish-speaking patients with lower limb musculoskeletal conditions. The results support the findings of previous original-English, Spanish, and Turkish versions for internal consistency, validity, reliability, error score, and factor structure.

Background: Patient reported outcome measures (PROMs) are recommended to enable the standardization of collected data and provide accurate representation of the patients’ subjective opinions of their functional capabilities. The purpose of this study was to perform linguistic and cross-cultural adaptation to establish a Polish version of the Lower Limb Functional Index (LLFI), and to evaluate the psychometric properties of internal consistency, reliability, error score, validity, and factor structure with standardized criteria PROMs in a population with lower limb problems.Methods: Linguistic and cultural adaptation complied with the International Society for Pharmacoeconomics and Outcomes Research (ISPOR) guidelines to produce the Lower Limb Functional Index - Polish version (LLFI-PL). This was a two-stage, cross-sectional study with repeated measures on two variables during retest examination. The study recruited n=125 subjects (age =52.86±19.53 years, range 20-87, 56% female, injury duration =17.69±18.39 weeks, range 5-71). Baseline reliability and construct validity included the LLFI-PL, Western Ontario and McMaster University Osteoarthritis Index (WOMAC), Euroqol Health Questionnaire 5-Dimensions (EQ-5D-5L), and an 11-point pain Numerical Rating Scale (NRS), with retest at 3-7 days. Practicality for readability was considered within the face and content validity. Completion and scoring time were also calculated. Results: Statistical analysis showed high internal consistency (α=0.94) that is below the 0.95 threshold limit, and excellent test-retest reliability (ICC2.1=0.96). The error score found the SEM=4.85% with MDC90=11.3%. Validity analysis showed strong correlations between the LLFI-PL with the WOMAC (r=-0.81) and moderate with the EQ-5D-5L (r=-0.63). Exploratory factor analysis confirmed a single-factor structure. Times for completion (172±33 seconds) and scoring (20±9 seconds) were determined.Conclusions: The LLFI-PL is a psychometrically sound questionnaire for Polish-speaking patients with lower limb musculoskeletal conditions. The results support the findings of previous original-English, Spanish, and Turkish versions for internal consistency, validity, reliability, error score, and factor structure.