Changes in Physical Activity, Sleep and Knee Function After Same-Day Discharge Knee Arthroplasty

Inclusion Criteria: \- Primary knee osteoarthritis: medial or lateral Kellgren Lawrence grade 3-4 for TKA and antero-medial grade 3-4 for UKA. Patient criteria for outpatient knee arthroplasty (UKA or TKA): * Full overnight support by an adult at home after discharge * At most mild, well-controlled, comorbidities (e.g. hypertension, hypothyroidism, epilepsy, asthma) * ASA-class 1-2 * Age \<80 years * BMI \<35 kg/m2 Exclusion Criteria: * Post-traumatic osteoarthritis * Neurological disorder aVecting walking or muscle strength * Inability or unwillingness to use a smartphone or to participate in the study Exclusion criteria for outpatient surgery: * History of cardiac or cerebrovascular events * Conditions affecting consciousness (e.g. syncope of cardiac origin) * Untreated or central sleep apnoea * Heart failure * Diabetes mellitus type 1 * Cognitive impairment or dementia * History of substance abuse * Chronic strong opioid therapy or severe pain disorder * Antithrombotic therapy (e.g. Xarelto, Pradaxa, Plavix or ASA for secondary prevention) * History of venous thromboembolism or known coagulopathy