Inclusion Criteria:  All patients undergoing primary knee arthroplasty (e.g., total, unicondylar and patellofemoral) reported in the Dutch Arthroplasty Register. Patients who filled out the NRS pain score, EQ-5D 3L or EQ-5D 5L pain score or EQ-5D anxiety/depression score.  Exclusion Criteria:  Other types of (revision) arthroplasty (hip / shoulder / ankle) Patients who did not fill out the NRS pain score, EQ-5D (3L or 5L) pain score or EQ-5D (3L or 5L) anxiety/depression score