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in the study once written informed consent was obtained. Included patients were
considered lost to follow-up in the study, if; (1) they did not return the questionnaires
on 2 consecutive follow-up points, (2) on 2 consecutive follow-up points returned 2 questionnaires that were less than half completed or (3) their contact details were
no longer valid and could not be ascertained.
Outcome measures and study procedures in the LOAS study
A set of PROMs were collected in consecutive adult patients scheduled for THA or TKA preoperatively and 6, 12, and 24 months after surgery and every 2 year thereafter. The PROMs were collected alongside the data collection of The Dutch Arthroplasty Register (Landelijke Registratie Orthopedische Implantaten, LROI, http://www.lroi.nl/en/home).
Sociodemographic and clinical characteristics
The following data were gathered: age, sex; weight (kg) and length (m) to calculate the Body Mass Index (BMI); and work status (working/retired/housewife or -man/ unemployed and/or seeking work/receiving disability benefits).
PROMs as advised by the Dutch Orthopaedic Association
The Hip disability and Osteoarthritis Outcome Score (HOOS), the Knee injury and Osteoarthritis Outcome Score (KOOS) and the Oxford Hip Score (OHS) and the Oxford Knee Score (OKS) were used for the preoperative and postoperative assessment of pain, limitations-daily living, sport and recreation, joint function and joint related quality of life. We used the validated Dutch versions of the HOOS, KOOS and OHS and OKS. 12,14-16
The Short Form-12 (SF12) and the EuroQol Visual Analogue Scale (EQ- VAS) were used to assess general health related quality of life. From the SF12 summary component scores for physical health (PCS) and mental health (MCS) were calculated. In this study, scores of a Dutch general population were used to standardize our scores in order to apply the norm-based scoring.17;18
The following additional assessments were also included for the LOAS cohor t but are not repor ted in this study : (a) comorbidities assessed by means of the comorbidity questionnaire from the Dutch Central Bureau of Statistics19; (b) a self-developed questionnaire to assess work status; (c) physical activity determined by the Short
feasibility of collecting multiple PROMs
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