Translation and Validation of the Spanish Version of the Norwich Patellofemoral Instability (NPI) Score

The Norwich Patellofemoral Instability (NPI) score is a disease-specific questionnaire for patients with this condition; however, it has not been validated in Spanish-speaking patients. To (1) translate the NPI score into Spanish and validate its psychometric properties and (2) to correlate it with the Spanish versions of the Kujala score and the Banff Patellofemoral Instability Instrument (BPII) 2.0. Cohort study (Diagnosis); Level of evidence, 2. The translation and validation of the NPI score into Spanish were conducted following the Consensus-Based Standards for the Selection of Health Measurement Instruments guidelines. This included forward and backward translations, conciliation, and a pilot study in 5 patients. Internal consistency was evaluated using the Cronbach alpha and test-retest reliability using intraclass correlation coefficients (ICCs). Pearson correlation coefficients were used to calculate the correlation of the NPI score with Kujala and BPII scores. The study included 58 voluntary participants, predominantly female (71%), with a mean ± SD age of 17.4 ± 6.6 years. The Spanish version of the NPI showed high internal consistency (Cronbach alpha, .93) and an ICC of 0.88 (95% CI, 0.80-0.92). Additionally, it exhibited a moderate negative correlation with the Kujala score (-0.57), and high negative correlation with the BPII score (-0.70). There was no ceiling or floor effect. Our study demonstrated that the Spanish version of the NPI score has high internal consistency and test-retest reliability, enabling its use in Spanish-speaking patients with patellar instability. It also demonstrated high correlation with another disease-specific score for patellofemoral instability (BPII 2.0) and moderate correlation with the Kujala score.