# Validity and reliability of the Flare-OA scale for hip and knee osteoarthritis in a Turkish population: item reduction with Rasch analysis

## TL;DR

This study validated and shortened the Flare-OA questionnaire for assessing osteoarthritis flares in Turkish patients, showing it is reliable and useful for both knee and hip OA.

## Contribution

The study provides a culturally adapted and item-reduced 16-item Flare-OA version for Turkish populations with high reliability and validity.

## Key findings

- The 16-item Flare-OA version showed high internal consistency (Cronbach’s alpha 0.972) and strong test-retest reliability (ICC 0.912).
- The Flare-OA scores significantly differentiated between patients with and without flare symptoms.
- The 16-item version demonstrated good sensitivity to change and strong correlations with existing OA outcome measures.

## Abstract

The Flare-OA questionnaire is a self-reported instrument developed to assess flare in individuals with knee and/or hip osteoarthritis. This study aimed to translate and culturally adapt both the original and short versions of the Flare-OA into Turkish.

The Turkish version of the questionnaire was obtained through a process of cross-cultural adaptation and translation. Patients aged 45 years or older with clinically and radiologically confirmed OA of the knee or hip were recruited. The Flare-OA scale, originally consisting of 33 items, was shortened to 19 items and then to a final 16-item version through Rasch analysis. The internal consistency of the Flare-OA was measured using Cronbach’s alpha, and its stability over time was tested by evaluating test–retest reliability over a 15-day interval in patients with no clinical changes. The sensitivity to change was determined by calculating the standardized response mean (SRM) in those who reported symptom variation during the follow-up. Convergent validity was assessed by analyzing the correlations between the scale and previously validated measures, including the Hip Disability and Osteoarthritis Outcome Score (HOOS-PS), the Knee Injury and Osteoarthritis Outcome Score (KOOS), and the Mini-Osteoarthritis Knee and Hip Quality of Life Questionnaire (Mini-OAKHQOL).

The study included 185 participants, of whom 71.9% were women, with a mean age of 63.2 years (SD:9.1). Of these, 160 patients (86.5%) had knee OA and 25 (13.5%) had hip OA. In the past four weeks, 70 patients (37.8%) reported a worsening of symptoms in the affected joint. Cronbach’s alpha coefficient was 0.987 (95% CI 0.984–0.990) for the 33-item and 0.972 (95% CI 0.966–0.978) for the 16-item. The intraclass correlation coefficient was 0.913 and 0.912 for the test-retest reliability (n=79) of the 33- and 16-item tests, respectively. Sensitivity to change was good in 9 patients with flare improvement [SRM 1.2 (95% CI 0.6–1.7), SRM 1 (95% CI 0.5–1.5), for 33- and 16-items, respectively] over the period. Discriminant validity was supported by statistically significant score differences between patients with and without flare for both the 33-item [36.2; 95% CI 29.9–42.6; SEM: 8; p<.0001] and the 16-item [36.7; 95% CI 30.3–43.0; SEM: 8.1; p<.0001] versions. There was a significant and negative correlation between the Flare-OA score and KOOS and mini-OAKHQOL (p<0.05). 16-item Rasch modeling allowed us to reduce the questionnaire to a 16-item version with good fit and a satisfactory interval scale.

The Turkish versions of the Flare-OA questionnaires (33- and 16-item) showed high reliability, validity, and clinical utility in evaluating flares in knee and hip OA. The 16-item version appears especially useful for routine use, although further validation is needed due to the limited sample size in the hip OA subgroup.

The online version contains supplementary material available at10.1007/s00296-025-05914-3.