Dutch translation and validation of the Norwich Patellar Instability score and Banff Patella Instability Instrument in patients after surgery for patellar instability.

Recently, two new English specific patient reported outcome measures (PROMs) to evaluate treatment of patients with patellofemoral complaints have been developed : the Banff Patella Instability Instrument (BPII) and the Norwich Patellar Instability (NPI) score. This study was designed to translate and validate the BPII and NPI in Dutch patients after surgical treatment for patellar instability. Forward and backward translation of the outcome measures was performed. Patients who had been surgically treated for patellar instability filled out the NPI and BPII together with the Kujala Knee Score, numeric rating scales, Knee disability and Osteoarthritis Outcome Score (KOOS) and SF- 36. We assessed internal consistency and construct validity. We evaluated the presence of ceiling and floor effects. Ninety-seven patients completed the online questionnaires. The internal consistency of the NPI and BPII score was excellent for both outcome measures. The BPII and NPI had good correlations with other PROMs. For the BPII we found no floor nor ceiling effect. For the NPI we found a floor effect but no ceiling effect. Our results indicate that the Dutch version of the BPII and the NPI can be used for patients with patellar instability. Both PROMs have specific (dis) advantages.