Adaptation of the Banff Patellofemoral Instability Instrument (BPII) 2.0 into Swedish

Background and purpose - The Banff Patellofemoral Instability Instrument (BPII) 2.0 is a patient-reported outcome measure (PROM) designed specifically for patellofemoral instability. We translated and adapted the BPII 2.0 into Swedish and assessed its psychometric properties.Patients and methods - The BPII 2.0 was forward and back-translated. Children aged 10-16 years with patellar dislocation and instability or recurrent dislocation were recruited. Children completed the Swedish BPII 2.0 and KOOS-Child during their initial visit (t0) and 1 week later (t1). Internal consistency and test-retest reliability were evaluated using intraclass correlation coefficients (ICCs) for the BPII 2.0 and KOOS-Child scores comparison. Pearson correlation coefficients examined concurrent validity of the Swedish BPII 2.0 subscales with KOOS-Child subscales.Results - 64 children (46 females), mean age 13.8 (10.0-16.3) years, participated. Time after patellar dislocation or surgery was 3-24 months. 55 patients (86%) returned the second BPII 2.0 and KOOS-Child after an average of 9 (5-22) days. There were no ceiling or floor effects for the total score of the new Swedish BPII 2.0 or for its subscales. BPII 2.0 demonstrated excellent internal consistency at t0 (ICC 0.96, 95% confidence interval [CI] 0.95-0.97) and at t1 (ICC 0.97, CI 0.95-0.98), as well as excellent test-retest reliability (ICC 0.97, CI 0.96-0.98). Concurrent validity of the BPII 2.0 subscales with KOOS-Child subscales was moderate to strong (rho 0.40-0.88).Conclusion - The Swedish BPII 2.0 showed excellent internal consistency as well as excellent test-retest reliability and is a reliable and valid questionnaire.