BIRMINGHAM – What is the pain experience after total knee arthroplasty and how does it affect outcome six to 12 months later?

That is the question raised in an article in JAMA Network Open.  The Birmingham, AL, VAMC and University of Alabama at Birmingham researchers sought to examine patterns of individual post-TKA pain trajectories and to assess their independent associations with longer-term pain outcome after TKA.1

The prospective cohort study combined data from a national TKA cohort with ancillary pain severity data at two weeks and eight weeks after the index surgery 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, which was the University of Massachusetts Medical School.

Patients had a date of surgery between May 1, 2013, and Dec. 1, 2014, with data analysis was performed between Jan. 13, 2015, and July 5, 2016.

The focus was on index knee pain at six months after TKA using the Knee Injury and Osteoarthritis Outcome Score (KOOS) pain scale. In addition, researchers used group-based trajectory methods to examine the presence of pain trajectories in the postoperative period, defined as eight weeks, and assessed whether trajectories were independently associated with longer-term pain at six months.

The cohort included 659 patients who underwent primary TKA with complete data at four points — preoperative, two weeks, eight weeks, and 26 weeks. Participants had a mean age of 67.1, and 64.5% were female. Mean body mass index was 30.77, most of the participants were white and their 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.

At eight weeks after TKA, two pain trajectory subgroups were identified:  patients who experienced fast pain relief in the first eight weeks after surgery, denoted as fast pain responders, comprising 72.4% [477 of 659] of the sample; and patients who did not, denoted as slow pain responders, comprising 27.6% [182 of 659] of the sample.

After adjusting for patient factors, researchers determined that the pain trajectory at eight weeks after TKA was independently associated with the mean KOOS pain score at six 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 six months after TKA compared with that among fast pain responders,” the authors wrote. “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.”

  1. Singh JA, Lemay CA, Nobel L, Yang W, Weissman N, Saag KG, Allison J, Franklin PD. Association of Early Postoperative Pain Trajectories With Longer-term Pain Outcome After Primary Total Knee Arthroplasty. JAMA Netw Open. 2019 Nov 1;2(11):e1915105. doi: 10.1001/jamanetworkopen.2019.15105. PubMed PMID: 31722026.