High pain reported at 3 months post-total knee arthroplasty often persists for the next 3 years and is associated with reduced function and quality of life.

Background And Aims: Five to ten percent of people having a knee arthroplasty for osteoarthritis continue to experience high pain levels more than 3 months after surgery. The primary aim of this study was to determine the relative risk (RR) of having high pain at 12 and 36 months based on the presence of high pain at 3 and 12 months, respectively.

Methods: A retrospective analysis of data from a prospective study of participants who had a total knee arthroplasty for osteoarthritis. A score of ≤14 on the Oxford Knee Pain Subscale was defined as 'High Pain', and RRs were calculated comparing those with high or low pain.

Results: There were 718 participants and 13.8% reported high pain at any time point, 2.5% reported high pain at all time points and 10.3% and 4.7% and 6.6% reported high pain at 3-, 12- and 36-months, respectively, post-surgery. For participants with high pain at 3 months, 33.8% had high pain at 12 months with a RR of 24.2 (95% CI 11.7-49.8, p < 0.001) and 35.1% had high pain at 36 months with a RR of 10.8 (95% CI 6.4-18.2, p < 0.001). For participants with high pain at 12 months, 67.6% had high pain at 36 months, with a RR of 19.3 (95% CI 12.2-30.4, p < 0.01).

Conclusions: Although high pain rates are low overall following knee arthroplasty, once high pain is established there is an elevated RR of it persisting at 12- and 36 months post-surgery.

Trial Registration: The data were collected in the Evidence-based Processes and Outcomes of Care (EPOC) study, ClinicalTrials.gov Identifier: NCT01899443.