There are few studies investigating the effects of acute postoperative pain on functional outcomes after total knee arthroplasty (TKA). The aims of this study are to identify perioperative factors associated with increased early postoperative pain and investigate the effects of acute postoperative day 1 and 2 pain on outcomes at 6 months and 2 years post-TKA.
1041 unilateral TKA patients were included in this retrospective cohort study. Patients were categorized into minor (visual analog scale: VAS <5) and major (VAS ≥5) pain groups based on postoperative day 1/2 VAS scores. Patients were assessed preoperatively, at 6 months and 2 years using Knee Society Knee Score and Function Scores (KSFS), Oxford Knee Score (OKS), SF-36 physical and mental component score (SF-36 PCS), expectation and satisfaction scores. Perioperative variables including age, gender, race, body mass index, American Society of Anesthesiologist status, type of anesthesia, and presence of caregiver were analyzed as predictors of postoperative acute pain. Wilcoxon two-sample test was used to analyze outcomes significantly associated with "major pain." Multiple logistic regression was used to identify predictors of "major pain."
Patients with "minor pain" had significantly better KSFS, Knee Society Knee Score, OKS, and SF-36 PCS scores at 6 months and significantly better KSFS, OKS, SF-36 PCS, and satisfaction at 2 years (P < .05). A significantly higher percentage of patients with "minor pain" met the minimal clinically important difference for SF-36 PCS at 6 months and KSFS at 2 years (P < .05). Women, Indian/Malay race, higher BMI, and use of general over regional anesthesia were independent predictors of getting "major pain" (P < .05).
Patients should be counseled about risk factors of postoperative pain to manage preoperative expectations of surgery. Patients should be managed adequately using multimodal pain protocols to improve subsequent functional outcomes while avoiding unnecessary opioid use.