Jordy van Sambeeck

Dutch translation and validation of the NPI score and the BPII 8 125 Introduction Instability of the patella may lead to serious impairment and most patients seek doctors advise how to best treat their complaints. To evaluate outcome of treatment of these patients, knee specific patient reported outcome measures can be used. Historically, 1 the modified International Knee Documentation Committee (IKDC) knee ligament standard evaluation form 2 , Kujala anterior knee pain scale 3 , Knee disability and Osteoarthritis Outcome Score (KOOS) 4 , Lysholm knee scoring scale 5 and Short Form-36 (SF-36) 6 were used. Smith et al. 7 stated that: “there is no outcome that is clinically meaningful” because the reliability and validity of these measurements for this patient category is poor. Recently two new outcome measures have been developed. Hiemstra et al. 8 devised the Banff Patella Instability Instrument (BPII). Validation of this outcome measure was performed in a Canadian population of patients with recurrent patella dislocations in whom non-surgical management had failed. The authors evaluated the score according to the Consensus based Standards for the Selection of Health Measurements Instruments (COSMIN) guidelines 9, 10 and demonstrated good face and content validity, high internal consistency, excellent reliability and construct validity in their population 8 . Concurrent validation, responsiveness and factor analysis and item reduction of the BPII lead to the creation of the BPII 2.0 11 . Another recently introduced score, the Norwich Patellar Instability (NPI) score 12 , was validated on patients with patellar instability, either preoperatively or postoperatively. The initial results of the COSMIN guidelines criteria for this score indicated a good convergent and divergent validity and high internal consistency 12 . In a second validation study the score showed a high convergent validity, internal consistency and good concurrent validity. 13 An essential requirement of all measurements in clinical practice and research is that they are reliable and valid. Reliability is defined as ‘the degree to which the measurement is free frommeasurement error’ 14 . Validity is defined as ‘the degree to which an instrument truly measures the construct it purports to measure’. 14 A Dutch validated subjective outcome score for patients with patella instability and patellofemoral pain is lacking. It would allow for the determination of the efficacy of a specific treatment, and for comparison of different methods of treatment in patients with the same disorder. Furthermore, it may enable clinicians to follow the progress of patients before and after a particular treatment. This study was designed to translate and validate the BPII and NPI in Dutch, with patients who have undergone surgical treatment for patellar instability and evaluate the internal consistency, construct validity and ceiling or floor effects.