The Danish version of the anterior knee pain scale (Kujala-DK): translation, cross-cultural adaptation and psychometric evaluation in patients with patellar instability

Purpose The aim of this study was to translate and cross-culturally adapt the Kujala into Danish (Kujala-DK) and investigate its psychometric properties in Danish patients with patellar instability.Materials and Methods Content validity was assessed through 22 think-aloud cognitive interviews involving 15 patellar instability patients, 5 with patellofemoral pain, and 2 healthcare professionals. Data from 100 patellar instability patients were analysed to assess construct validity, internal consistency, test-retest reliability, floor and ceiling effects and minimal detectable change. Structural validity was assessed using confirmatory factor analysis (CFA). Construct validity was evaluated via Spearman’s Rho. Internal consistency was evaluated with Cronbach’s alpha and test-retest reliability with ICC in 57 patients who completed the Kujala twice, 7 days apart. The methods followed established guidelines.Results Patients found Kujala-DK relevant, comprehensible, and comprehensive. Items 11 and 12 were rephrased. CFA supported a unidimensional factor structure, with loadings ranging from 0.25 to 0.86. High correlations with IKDC and VISA-P and moderate agreement with TAS were observed. Internal consistency (α = 0.87) and test–retest reliability (ICC = 0.94) were high. The minimum detectable change was 13.0 points.Conclusions The Kujala-DK demonstrate adequate construct validity and reliability and is recommended for clinical and research use in Danish-speaking patellar instability patients.