Abstract
Studies to date have not comprehensively examined pain experience after total knee arthroplasty (TKA). Discrete patterns of pain in this period might be associated with pain outcomes at 6 to 12 months after TKA. To examine patterns of individual post-TKA pain trajectories and to assess their independent associations with longer-term pain outcome after TKA. This prospective cohort study combined data from a national US TKA cohort with ancillary pain severity data at 2 weeks and 8 weeks after the index TKA using a numeric rating scale. All participants received primary, unilateral TKA within the Function and Outcomes Research for Comparative Effectiveness in Total Joint Replacement (FORCE-TJR) national network of community sites in 22 states or at the lead site (University of Massachusetts Medical School). Participants had a date of surgery between May 1, 2013, and December 1, 2014. The data analysis was performed between January 13, 2015, and July 5, 2016. Pain trajectories in the postoperative period (8 weeks). Index knee pain at 6 months after TKA using the Knee Injury and Osteoarthritis Outcome Score (KOOS) pain scale. Group-based trajectory methods examined the presence of pain trajectories in the postoperative period (8 weeks) and assessed whether trajectories were independently associated with longer-term pain (6 months). The cohort included 659 patients who underwent primary TKA with complete data at 4 points (preoperative, 2 weeks, 8 weeks, and 26 weeks). Their mean (SD) age was 67.1 (8.0) years, 64.5% (425 of 659) were female, the mean (SD) body mass index (calculated as weight in kilograms divided by height in meters squared) was 30.77 (5.66), 94.5% (613 of 649) were white, and the mean (SD) preoperative 36-Item Short Form Health Survey physical component summary and mental component summary scores were 34.1 (8.2) and 53.8 (11.4), respectively. Two pain trajectory subgroups were identified at 8 weeks after TKA: patients who experienced fast pain relief in the first 8 weeks after TKA (fast pain responders, composing 72.4% [477 of 659] of the sample) and patients who did not (slow pain responders, composing 27.6% [182 of 659] of the sample). After adjusting for patient factors, the pain trajectory at 8 weeks after TKA was independently associated with the mean KOOS pain score at 6 months, with a between-trajectory difference of -11.3 (95% CI, -13.9 to -8.7). The trajectory among slow pain responders at 8 weeks after surgery was independently associated with improved but greater persistent index knee pain at 6 months after TKA compared with that among fast pain responders. Early identification of patients with a trajectory of slow pain response at 8 weeks after TKA may offer an opportunity for interventions in the perioperative period to potentially improve the long-term pain outcomes after TKA.
Highlights
Total knee arthroplasty (TKA) is one of the most common elective surgical procedures performed in older patients to treat pain and functional limitation owing to refractory knee arthritis[10] and is associated with optimal arthritis pain relief in most but not all patients
Research to date is limited by single-center enrollment, small sample sizes with high dropout rates, and the lack of adjustment for common confounders
Factors Associated With Post-total knee arthroplasty (TKA) Pain Trajectories Two pain trajectory subgroups were identified at 8 weeks: fast pain relief in the first 8 weeks after TKA and no fast pain relief (Figure)
Summary
Total knee arthroplasty (TKA) is one of the most common elective surgical procedures performed in older patients to treat pain and functional limitation owing to refractory knee arthritis[10] and is associated with optimal arthritis pain relief in most but not all patients. In the United States, 8% to 15% of patients who undergo TKA have residual moderate to severe index joint pain that persists 2 to 5 years after the procedure.[11,12] A systematic review concluded that unfavorable longterm pain outcomes were seen in 10% to 34% of patients after knee arthroplasty.[13] Few studies have examined intermediate-term postoperative pain and its association with long-term pain outcomes. In 2 studies, researchers used preoperative and postoperative pain and function scores to assess pain outcome at 5 years after TKA15 or used preoperative scores to assess pain outcome at 3 months and 12 months after TKA16; these studies focused on preoperative pain and did not collect postoperative pain data (within 2 to 3 months of TKA).[15,16] In addition, research to date is limited by single-center enrollment, small sample sizes with high dropout rates, and the lack of adjustment for common confounders (eg, race/ethnicity, body mass index [BMI; calculated as weight in kilograms divided by height in meters squared], and comorbidities)
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