Motivational Feedback Following Total or Unicompartmental Knee Arthroplasty

The goal of this randomized controlled trial (RCT) nested in a prospective cohort study is to investigate whether physical activity (PA) following total knee arthroplasty (TKA) or unicompartmental knee arthroplasty (UKA) can be optimized by the use of an activity tracking device including motivational feedback in comparison with activity tracking without feedback. Furthermore, the project will investigate the predictive value of PA level prior to TKA/UKA for the length of stay, return to work, and quality of life. The main hypothese of the study are: RCT study: * Using an activity tracking device, including motivational feed-back on PA show a superior short-term effect on increased PA (Total counts; primary outcome measure), physical functioning, return to work, and quality of life in comparison with no motivational feed-back from the activity tracker, defined as 'care as usual', in TKA and UKA patients * Using an activity tracking device, including motivational feedback, will have a superior effect on step counts, activity types and pain compared to the standard care, in TKA and UKA patients Prospective cohort: * PA prior to TKA or UKA can work as a predictive measure for function and quality of life following surgery * PA prior to TKA or UKA can work as a predictive measure for the length of hospital stay and return to work Patients will be randomized to activity tracking and motivational feed-back by gamification for patient self-mobilization (Intervention-group) or 'care-as-usual' including activity tracking without motivational feed-back (Control-group). Patients not eligible and/or willing to participate in the RCT study, will be offered to participate in a prospective non-interventional cohort study.

Inclusion Criteria: 1. Age: 40-85 years 2. patients scheduled for primary TKA or UKA 3. understanding both verbal and written Danish language. Exclusion Criteria: 1. Difficulty adhering to the study protocol 2. Refusal of standard care 3. Known- or newly diagnosed malignancy or palliative care 4. Participation in an interventional clinical trial during the last 3 months potentially interacting with the aims of the current study. 5. Do not own a smartphone