The Norwich Patellar Instability score: Validity, internal consistency and responsiveness.

Background/Aims: This study assessed the validity, internal consistency, responsiveness and floor-ceiling effects of the Norwich Patellar Instability (NPI) score for a cohort of conservatively managed people following first-time patellar dislocation (FTPD). Methods: Fifty patients were recruited, providing 130 completed datasets over 12 months. Patient NPI score, Lysholm Knee score, Tegner Level of Activity score and isometric knee extension strength were assessed at baseline, 6 weeks, 6 and 12 months post-injury. Results: There was high convergent validity with a statistically significant correlation between NPI and Lysholm Knee score (p<0.001), Tegner Level of Activity score (p<0.001) and isometric knee extension strength (p<0.002). Principal component analysis revealed the NPI demonstrated good concurrent validity, with four components accounting for 70.4% of the variability. While the NPI demonstrated a floor effect for 13 of the 19 items, no ceiling effect was reported. There was high internal consistency, with a Cronbach a value of 0.93 (95% CI 0.91-0.93). NPI score was responsive to change over the 12-month period, with an effect size of 1.04 from baseline to 12 months post-injury. Conclusions: The NPI can be considered a valid and responsive outcome measure to assess patellar instability symptoms for people conservatively managed following FTPD. The high floor effects reported in this study need further exploration to improve the ability of the NPI to detect people with lower perceived instability symptoms. [ABSTRACT FROM AUTHOR]