Jordy van Sambeeck

Dutch translation and validation of the NPI score and the BPII 8 127 The Norwich Patella Instability score (NPI) consists of 19 items scoring instability for lower-and higher-energy activities to assess perceived patellar instability. It was based on a previous study assessing activities the aggravated symptoms in patients with patella instability 19 All patients in the validations study had at least one patella dislocation. The score consists of a five-point Likert scale ranging from ‘always’ to ‘never’. The score is ranges from 0 to 250. The total score is then converted to a percentage based on the number of scored responses provided. A higher percentage indicates higher severity of patellar instability. The SF-36 is a patient-administered, generic HRQL (health related quality of life) instrument. It comprises 36 items across eight dimensions (physical functioning, role/emotional functioning, role/social functioning, role physical/functioning, bodily pain, vitality, general health and mental health perceptions. The eight dimensions of the SF-36 score are calculated on a 0 to 100 scale (100 indicating no symptoms and 0 indicating extreme symptoms). The Kujala Knee Score investigates 13 domains. The score ranges from 0-100 with a higher score indicating better performance. The KOOS is a 40-item questionnaire for evaluating symptoms and restrictions in patients with knee related complaints. The questions cover five domains; symptoms (5 items), pain (10 items), activities of daily living (17 items), sports and recreation (4 items) and quality of life (4 items). Answers are on a 5-point Likert scale. Higher scores related to fewer complaints. The NRS was obtained through a horizontal line of 100 mm. Two dimensions of pain will be assessed; pain during activity and pain at resting. Additionally, an NRS will be used to assess instability and disability resulting from patellofemoral pain over the last week. The patient was free to put a digital point on the line. This point was transferred to a length from 0 to that point in millimeters. A NRS score of 0 meant no pain, no disabilities and a score of 100 meant worst pain and fully disabled respectively. As measure of reliability we assessed internal consistency (the degree of interrelatedness among the items). It qualifies the extent to which items assess the same construct and is quantified using Cronbach’s alpha test, which ranges from 0 to 1. A value of more than 0.7 is considered acceptable 20 . The Dutch NPI and BPII were compared to the SF-36, NRS scores for pain and disability, Kujala and the KOOS. The Spearman correlation tests was calculated for the assessment of construct validity. Convergent validity was tested by hypothesizing strong (r > 0.5) (Spearman) correlations between the NPI or BPII and questionnaires that measure similar constructs like the KKS, KOOS and three physical domains of the SF36 (physical functioning, role limitations due to physical problems, bodily pain). Divergent validity will be tested by hypothesizing weak (r < 0.3) correlations between the NPI or BPII and questionnaires that are expect to measure different constructs, like the mental domains of the SF36.