Jordy van Sambeeck

Chapter 8 126 Methods This study was presented to the institutional review board who deemed that the Medical Research Involving Human Subjects Act (WMO) does not apply. The translation of the scores was done according to the MAPI method 15 . The original versions of the NPI score and BPII were translated from English to Dutch by two bilingual independent native Dutch persons (a PhD-student and amedical student). In a meeting with a third person (an orthopedic surgeon) discrepancies between these two forward translations were discussed and consensus was achieved. The final Dutch version was translated back into English by an independent (non-medical) native-English speaking person blinded for the original English version of the questionnaires to ensure content validity. Discrepancies between this backward translation and the original version were reviewed and discussed by two researchers, but no inconsistencies were found. In a pilot series clarity, understandability, acceptability of the questionnaire was evaluated in a group of 15 patients before the actual study commenced. No changes were necessary and both PROMs were deemed ready for validation. Patients data from other retrospective studies in our center was used. All included patients had been surgically treated for patellar instability in Radboudumc between 2005 and 2015. The surgical procedures included trochlear osteotomy, tibial tubercle transposition and/or medial patellofemoral ligament reconstruction. Patients were contacted by letter and by phone for informed consent, after inclusion the patients were directed to a protected website to fill out several patients reported outcome measures (PROMs). All questionnaires contained the translated Norwich patella instability score and Banff patella instability instrument, a validated Dutch version of the Kujala Knee Score (KKS) 16 , Knee disability and Osteoarthritis Outcome Score (KOOS) 4 , SF-36 6 and a Numeric Rating Scale (NRS) for pain and disability for determination of the construct validity. The Banff Patella Instability Instrument (BPII) is a disease specific quality of life measurement designed specifically for patients with patellofemoral instability. It is based on the Anterior Cruciate Ligament-Quality of Life questionnaire (ACL- QOL) 17 , and contains the following items: symptoms and physical complaints, work, sport/recreation/competition, lifestyle, social and emotional. Each of these items can be scored by the patient on a 0 to 100 scale. Validation studies were done by designers of the instrument with patients not responding to conservative treatment who were referred for orthopedic consultation to consider operative treatment. For the English version the clinimetric and psychometric soundness of the scores were tested: content validity, internal consistency, floor and ceiling effect, test-retest 8 , concurrent validation to other scores 18 and to objective clinical measurements. The score has not been evaluated by other users. For this paper, the original 32 item score was used. After a recent factor analysis study a reduced 23 item version was published, but this was unavailable at the time of the current study.