Page 152 - The value of total hip and knee arthroplasties for patients

Chapter 8
first time; and (i) numbers of hours working per week after 1 year. If the follow-up questionnaire was returned incomplete, patients were contacted by telephone to provide the required information.
Health related quality of life
The Short Form 36 Health Survey questionnaire (SF-36) is composed of 36 questions and standardized response choices, organized into eight multi-item scales: physical functioning (PF), role limitations due to physical health problems (RP), bodily pain (BP), general health perceptions (GH), vitality (VT), social functioning (SF), role limitations due to emotional problems (RE) and general mental health (MH). From these eight subscales, the SF-36 mental and physical component scales (MCS and PCS) were computed. For that purpose, the method of norm-based scoring was used.17 In norm-based scoring, each scale is scored to have the same average (mean: 50) and the same standard deviation (SD: 10), meaning each point equals one-tenth of a standard deviation. In this study, scores of a Dutch general population18 were used to standardize the scores according to the method of norm-based scoring. Lower scores represent worse health status.
The Euroqol-5 Dimension (EQ-5D) is an instrument designed to derive from five dimensions of health (mobility, self-care, usual activities, pain and mood), a single cardinal index for the quality weighting of QALYs. The EQ-5D uses valuations derived with the time trade-off method from a large general population survey to score the five-dimension health profile self-reported.The second part Euroqol visual analogue scale (EQ-VAS) consists of a 20-cm vertical visual analogue scale (VAS) ranging from 100 (best imaginable health state) to 0 (worst imaginable health state).The EQ-VAS gives a self-assessed measure of overall health state.19
Functional outcome measurement
Hip and knee functions were assessed by means of the following outcome measures: (a) The Hip disability and Osteoarthritis Outcome Score (HOOS), consisting of 40 items divided over five dimensions: pain (P) (10 items), symptoms (S) including stiffness and range of motion (5 items), activity limitations—daily living (A) (17 items), sport and recreation function (SP) (4 items) and hip-related quality of life (Q) (4 items)20 The Knee injury and Osteoarthritis Outcome Score (KOOS) comprises 42 items and uses the same five subscales as the HOOS.21 For the present study, validated Dutch versions of the HOOS and KOOS were used.22
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