Dainty JR, Smith TO, Clark EM, et al. - Researchers conducted a prospective, longitudinal cohort sub-study within the National Joint Registry (NJR) in order to ascertain the trajectories of patient reported pain and functional disability over 5 years following total hip arthroplasty (THA) or total knee arthroplasty (TKA). Oxford Hip Score (OHS) and Oxford Knee Score (OKS) questionnaires were offered to a total of 20,089 patients who underwent primary THA and 22,489 who underwent primary TKA between 2009 and 2010, at 6 months, and 1, 3, and 5 years postoperatively. Two discrete trajectories for pain and function were described based on the data: ‘level 1’ responders (around 70% of cases) in whom a high level of improvement is sustained over 5 years, and ‘level 2’ responders who had sustained improvement, but at a lower level. Prediction of postoperative pain and function after THA and TKA cannot be reliably done using the available preoperative patient variables. Patient outcomes at 6 months postoperatively can aid in reliably determining outcome at 5 years.