Standard total knee arthroplasty will be performed.

The 30-second sit to stand test will be used to assess functional lower extremity strength. This test is performed using a chair of standard height without arms. The participant is encouraged to complete as many full stands as possible within 30 seconds.

The Brief Pain Inventory (BPI) will be used to measure pain (56). The BPI is a brief patient-completed questionnaire that consists of four items that measure pain intensity (on an 11-point numeric rating scale from 0-10), seven questions on pain interference with functioning, a body map to localize the pain and one item on pain relief.

The widely used EuroQol-5 (EQ-5D-5L) will be used to measure health-related quality of life.

The EQ5D-5L consists of two parts: A descriptive system (Mobility, self-care, usual activities, pain/discomfort and anxiety/depression) and the EQ-VAS that record patients self-rated health on a visual analog scale that range from 0 - 100, higher levels indicate better self-rated health.

The descriptive system can be converted to a single summary index number where lower levels indicate poorer health-related quality of life.

The Forgotten Joint Score will be used to assess how natural the prosthesis feels after total knee arthroplasty. The scoring system consists of 12 items that assess patients agreement with 12 statements, that range from 1 (never) to 5 (mostly). The raw score is transformed to a 0-100 score and then reversed to obtain the final score. A higher score indicate better outcome.

The Pain Catastrophizing scale (PCS) will be used to measure catastrophic thinking related to pain. The scale consist of 13 items that range from 0 -4. The PCS assesses three dimensions of catastrophizing (i.e., rumination (range 0-16), magnification (range: 0-12, helplessness (range 0 -24). Higher scores indicate higher levels of catastrophic thinking related to pain. A total score can be computed by summing responses to all 13 items. PCS total scores range from 0-52. Higher scores indicate higher levels of catastrophic thinking related to pain.

Patient-acceptable symptom state will be measured by a single item question. The patient state wether they consider their knee function satisfactory or not (Yes/No).

Perceived treatment failure will be measured by a single item question. The patient state whether their situation is so dissatisfying that they consider the treatment as a failure (Yes/No).

The patient rate their level of knee problems compared to their condition before they started their treatment, by choosing on of seven statements that describe the level of improvement/worsening.

The statements range from "better - an important improvement" - to "worse, an important worsening".

All events reported by participant, physiotherapist or documented in the patient's hospital record.

• During surgery: Number of patients with fractures (Tibia, patella, femur), nerve or vascular injury, rupture of patella tendon, other.
• Postoperatively: Number of patients with deep infection, any secondary surgery (e.g., skin necrosis or scar tissue adherences, DAIR, MUA, secondary insertion of patella component, partial/total revision surgery), supracondylar femur fracture, patella fracture, permanent n. peroneus paresis, aseptic loosening, polyethylene defect (tibia or patella), instability requiring intervention, thrombophlebitis demanding anticoagulant treatment, pulmonary embolism, myocardial infarction, cerebral insult, other events.
• Patient-reported myocardial infarction, cerebral insult, pulmonary embolism or DVT within 3 months following intervention.
• All events reported by patients or physiotherapists - open probe questionnairing

The Hospital Anxiety and Depression Scale (HADS) will be used to measure self-reported psychological distress (depression and anxiety). The scale consists of 14 items, 7 on the depression subscale and 7 on the anxiety subscale. The Norwegian version has excellent psychometric properties. Each subscale range from 0-21 where higher scores indicate higher levels of anxiety or depression. A total score (range 0 - 42) can be calculated from summarizing all the 14 items. Higher scores indicate higher levels of anxiety/depression.

The Fear-Avoidance Belief Questionnaire (FABQ) will be used to measure pain-related fear of movement. The instrument consists of 2 subscales, fear-avoidance beliefs for work, and fear-avoidance beliefs for physical activity (FABQ-PA). Only the FABQ-PA subscale will be used in this study. The FABQ-PA consists of 4 items where patients rate their agreement with 5 statements about pain and physical activity. The FABQ-PA range from 0-24 and higher scores indicate higher levels of pain-related fear of movement.

The Health Locus of Control Scale (HLCS) will be used to measure patients' anticipations between own health and disease behavior and consequences of the behavior. The scale consists of 18 statements. Patients rate their agreement on a 6 point likert scale ranging from disagrees completely to agrees completely. Scoring: The scoring system consists of 3 subscales: The Internal Locus of Control, the Powerful Others Health Locus of Control, and the Chance Health Locus of control. The scores are obtained by summing items for each subscale. Higher scores indicate stronger agreement or inclination towards that particular subscale.

Self-reported level of physical activity will be measured using two items from the Norwegian Hunt2 survey that assess frequency of light and hard physical activity, and the Stages of Change for physical activity. The Stages of Change for physical activity assess patients' readiness for physical activity. Patients rate their agreement with five different statements about physical activity.

The ActiGraph Professional single-axis accelerometer, a body worn sensor system to measure physical activity, will be used to measure time in sedentary and active positions, duration of activity and number of steps during walking

The 40 meter walk test: The patient is instructed to walk 40 meter under timing.

The Stair Climb Test will be used to measure ascending and descending stair activity, and lower body strength and balance, measured as a participants' time in seconds to ascend and descend a flight of stairs.

Use of health care resources will be measured using registry data from the KUHR-system (i.e., control and payment of reimbursements to health service providers), the Norwegian Patient Registry (NPR) FD Trygd social security database, the Norwegian Prescription Database and the Norwegian Arthroplasty registry. All information will be anonymized and linked to each patient using a code number before analysis.

X-rays including weightbearing AP, lateral view, Rosenberg view and long leg weightbearing AP view (HKA) weightbearing AP view (HKA). OA severity grading will be performed according to the Kellgren-Lawrence grading system and cartilage thickness.

Number of patients undergoing screening, considered for inclusion, eligible for inclusion, consenting to participate and undergoing randomization

Number of patients receiving the full dose of the intervention. adverse events, recruitment, screening and randomization, retention in study/loss to follow-up.

Number of patients feeling overwhelmed or burdened by the intervention. Number of patients not completing the intervention due to feeling overwhelmed ro burdened by the intervention.

The Electronic Health Literacy Questionnaire (e-HLQ) (44) will be used to measure patients level of electronic health literacy prior to, and six months following surgery. In this study, 4 domains will be assessed: 1) using technology to process health information, 2) understanding of health concepts and language, 3) ability to actively engage with digital services, 4) motivated to engage with digital services. The scores range 1-4, with high scores indicating high e-health literacy.

The International Health Literacy Population survey Questionnaire 2019-2021(HLS19-Q47) will be used to measure patients' level of health literacy prior to, and six months following surgery. The original HLS-19-Q47 consist of 47 items. In this study, 2 domains will be assessed: 1) Health promotion and 2) General health literacy.