Characteristics of Patients Declining INKA Trial Participation

The Oxford Knee Score (OKS) is a 12-item Patient Reported Outcome questionnaire developed specifically to assess the patient's perspective on the outcomes of knee arthroplasty (KA) with respect to combined pain and physical function. Standardized answer options are given (5 Likert boxes) and each question is assigned a score from 0 to 4. Thus, a total score is calculated that ranges from 0 and 48, with 48 indicating the best outcome.

EQ-5D-5L is a standardized patient-reported instrument for use as a measure of health outcome and quality of life. EQ-5D-5L is designed for self-completion by respondents and is ideally suited for use in surveys.

The EQ-5D-5L consists of a descriptive system and the EQ Visual Analogue scale (EQ VAS). The descriptive system comprises 5 dimensions (mobility, self-care, usual activities, pain/discomfort, and anxiety/depression). Standardized answer options are given (5 Likert boxes) and each question is assigned a score from 1 to 3. It is simple, taking only a few minutes to complete. Instructions to respondents are included in the questionnaire.

The EQ-5D VAS records the respondent's self-rated health on a 20 cm vertical, visual analogue scale with endpoints labelled 'the best health you can imagine' and 'the worst health you can imagine'.

At clinical outcome assessment visit, the participants will be interviewed by an investigator about their use of analgesics since last visit. The interview will be focused on intake of

• Paracetamol/acetaminophen
• NSAIDS
• Acetylic acids
• Opioids The use of these analgesics will be recorded as a 0-3 points Likert scale (0, never; 1, rarely; 2, 2-3 times per week; 3, daily or almost daily).

KOOS-12 provides scale scores for knee-specific Pain, Function and QOL, along with a summary measure of overall knee impact.

Each item is scored from 0 to 4, with 0 representing no knee problems and 4 representing extreme knee problems. The separate KOOS-12 Pain, Function and QOL scale scores are calculated, in which item responses are summed.

The KOOS-12 Summary knee impact score is calculated as the average of the KOOS-12 Pain, KOOS-12 Function and KOOS-12 QOL scale scores. A Summary impact score is not calculated if any of the three scale scores are missing. The KOOS-12 Summary impact score also ranges from 0 to 100, where 0 is the worst possible and 100 is the best possible score.

The participant's assessment of the impact of their knee on everyday life is measured as the response to the question "Taking into account all the activities you have during your daily life, your level of pain, and your functional impairment, how much does your [left/right] knee impact your daily life?". A 100 mm visual analogue scale (VAS) will be used as assessment instrument with anchors: 0 = "No impact" and 100 = "Worst imaginable impact".

The participants body weight is transferred from the medical records of their visit in the orthopaedic outpatient clinic.

B-IPQ is a generic 9-item questionnaire developed to rapidly assess the cognitive and emotional representations in a variety of illnesses. B-IPQ is a short version of the 84-item revised illness perception questionnaire (IPQ-R) (21). B-IPQ assesses perceptions on the following five dimensions: Identity, Cause, Timeline, Consequences and Cure-Control. Five of the items assess cognitive illness representations; two of the items assess emotional representations; and one item assesses illness comprehensibility. The 8 items are scored on a 0-3 Likert scale with descriptors (none or extreme) at either end.