Patients who undergo total knee arthroplasty (TKA) are more likely to experience higher levels of postoperative pain based on several preoperative factors, including rates of opioid use, fatigue severity, and illness perception. This is according to a study published in the European Journal of Pain.
In this longitudinal study, a total of 202 patients (mean age, 68 years) completed questionnaires on the day before TKA surgery that asked about both their average and worst pain on a 0 to 10 numeric rating scale, interference with functioning, fatigue, anxiety, depression, and perceptions of illness. Investigators assessed the average and worst pain scores before surgery, as well as on postoperative day 4 and postoperative weeks 6, months 3, and month 12 after surgery.
The first choice for anesthesia was spinal anesthesia with bupivacaine and sedation. The first choice for postoperative pain management was epidural analgesia with a continuous infusion of 1 mg/ml bupivacaine, 2 μg/ml adrenaline, and 2 μg/ml fentanyl (5-12 ml/hour).
Overall, the total sample had a mean pain score of 5.3 on postoperative day 4, which gradually decreased over a 12-month period after surgery. Growth mixture modeling was used to identify 2 subgroups with distinct mean and worst pain profiles.
Compared with patients in the lower average pain class (n=141), those in the higher average pain class (n=61) had higher preoperative pain scores compared with patients in the lower pain class. These scores increased in this class during the first 3 months after surgery followed by a slight reduction over the subsequent 9 months. In contrast, patients in the lower worst class reported moderate preoperative pain scores that decreased over the remaining 9-month period after TKA.
Compared with those in the lower pain classes, patients in the higher pain classes had higher mean and worst pain scores (Cohen’s d=0.44 and 0.29, respectively), higher pain interference with function scores (Cohen’s d=0.50), as well as higher number of painful sites at 12 months following TKA (Cohen’s d=0.29; P =.03).
Additionally, patients classified into the higher pain class more often used opioids before surgery, were more likely to receive a continuous nerve block and ketamine, had reported higher levels of preoperative fatigue severity and interference scores (Cohen’s d=0.46 and 0.36, respectively), and reported worse perceptions of illness (Cohen’s d=.42; P =.004).
One limitation of this study was the lack of assessment of other important risk factors, including pain catastrophizing, neuropathic pain features, expectations, and adherence with therapy.
“These risk factors may be useful as part of an evidence-based preoperative screening tool to identify patients at higher risk for more severe pain following surgery,” the researchers concluded. “Future studies should test whether modifying disease risk factors can improve patients’ outcomes after TKA.”
Lindberg MF, Miaskowski C, Rustøen T, Cooper BA, Aamodt A, Lerdal A. Preoperative risk factors associated with chronic pain profiles following total knee arthroplasty. Published online December 1, 2020. Eur J Pain. doi: 10.1002/ejp.1703