Trajectories of pain and function in the first 5 years after hip and knee joint replacement: an analysis of patient reported outcome data from the National Joint Registry of England, Wales, Northern Ireland and the Isle of Man

AIMS: To determine the trajectories of patient reported pain and functional disability over five years following total hip replacement (THR) or total knee replacement (TKR). METHODS: A prospective, longitudinal cohort sub-study within the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man (NJR) was undertaken. 20,089 patients who underwent primary THR and 22,489 who underwent primary TKR between 2009 and 2010 were sent Oxford Hip Score (OHS) and Oxford Knee Score (OKS) questionnaires at six months, one, three and five years post-operatively. OHS and OKS were disaggregated into pain and function subscales. A k-means clustering procedure assigned each patient to a longitudinal trajectory group for pain and function. Ordinal regression was used to predict trajectory group membership using baseline OHS and OKS score, age, BMI, IMD, gender, ethnicity, geographical location and ASA grade. RESULTS: Data described two discrete trajectories for pain and function: ‘Level 1’ responders (70% of cases) in whom a high-level of improvement is sustained over five years, and a ‘Level 2’ responders who sustained improvement, but at a lower level. Baseline patient variables were only weak predictors of pain trajectory and modest predictors of function trajectory. Those with worse baseline pain and function tended to show a greater likelihood of following a ‘Level 2’ trajectory. Six-month PROMs data reliably predict the class of five-year outcome trajectory for both pain and function. CONCLUSION: Reviewing patient outcomes at six months post-operatively is a reliable indicator of outcome at five years.