Cross-Cultural Adaptation and Validation of the Norwich Patellar Instability (NPI) Score and the Banff Patellofemoral...

Patellofemoral instability (PFI) is most prevalent in adolescents aged 10-17 years, yet disease-specific functional assessment tools validated for pediatric populations are limited. The Banff Patellofemoral Instability Instrument (BPII) 2.0 and the Norwich Patellar Instability (NPI) scores are disease-specific tools that have previously been validated in adults. The purpose of this study was to translate, culturally adapt, and validate the BPII 2.0 and NPI scores for Polish-speaking pediatric patients with PFI.

The Polish versions of the BPII 2.0 and NPI were developed following Beaton's cross-cultural adaptation guidelines. Patients aged 12-18 years with surgically treated recurrent patellofemoral joint instability completed the BPII 2.0, NPI, Anterior Knee Pain Scale (Kujala), Lysholm Knee Score, and Pedi-IKDC at a clinic visit and again 7-14 days later. The following psychometric properties were assessed: face validity, floor and ceiling effects, test-retest reliability (ICC), internal consistency (Cronbach's α), and construct validity (Spearman Correlation Coefficients).

A total of 57 postoperative patients (19 males, 38 females; median age 16 years, range 12.25-18 years) participated 24-36 months after surgical stabilization. No floor or ceiling effects were observed. The test-retest reliability was excellent (ICC = 0.988 for BPII 2.0 (95% CI 0.977-0.994, p < 0.001); ICC = 0.997 for NPI (95% CI 0.995-0.998, p < 0.001)). Both instruments demonstrated excellent internal consistency (Cronbach's α = 0.95 for BPII 2.0; α = 0.93 for NPI). The BPII 2.0 showed moderate to strong positive correlations with Lysholm (ρ = 0.69), Kujala (ρ = 0.69), and Pedi-IKDC (ρ = 0.57) and moderate negative correlation with NPI (ρ = -0.62), all of which were statistically significant (p < 0.001).

The Polish versions of the BPII 2.0 and NPI scores demonstrated excellent reliability (ICC = 0.988 and 0.997, respectively), internal consistency (Cronbach's α = 0.95 and 0.93, respectively), and construct validity in Polish-speaking adolescent patients with surgically treated recurrent patellofemoral instability. This is the first validation of the NPI in an exclusively pediatric population. These tools are suitable for clinical assessment and research in this specific population. Limitations include the postoperative-only cohort and absence of structural validity assessment.