Factors Associated With the Risk of Developing Moderate to Severe Acute Postoperative Pain After Primary Total Knee Arthroplasty: Results From the PAIN OUT Registry.

Background: Total knee arthroplasty (TKA) is one of the most common procedures in orthopedic surgery and not always matches with patient's expectations of pain relief and function improvement. The aim of this study was to assess risk factors for developing moderate to severe acute postoperative pain (APOP) after TKA using the PAIN OUT questionnaire.

Methods: Prospective, multicentre, international cohort study within the PAIN OUT project. Patients' outcomes were measured with 11-point numerical rating scales (0 = null, 10 = worst possible). Patient and analgesic/anesthetic treatment were assessed. Odds ratio for moderate-severe pain was calculated for each variable and if they were statistically significant in the univariate logistic model, variables were fitted into a multivariate logistic regression model. The effect size was assessed by Cohen's d coefficient.

Results: In total, 968 patients were evaluated. The multivariate model identified chronic preoperative pain (P < .001), general anesthesia (P = .020), and receiving chronic opioids before (P = .020) or after the surgery (P < .001) as factors associated with moderate-severe APOP. No protective factors were observed.

Conclusions: Our model identified several risk factors for APOP. From our results, preoperative chronic pain, general anesthesia and the use of opioid analgesics could be predictors for higher APOP. These findings may help establish new strategies for the treatment of pain in TKR. More studies should be carried out to identify acute pain predictors and to develop better strategies of pain management for risk patients.