Pain responses to 2 types of preoperative heat stimuli were not independent clinically relevant predictors for postoperative pain after total knee arthroplasty.
It has been estimated that up to 54% of the variance in postoperative pain experience may be predicted with preoperative pain responses to experimental stimuli, with suprathreshold heat pain as the most consistent test modality. This study aimed to explore whether 2 heat test paradigms could predict postoperative pain after total knee arthroplasty (TKA). Patients scheduled for elective, unilateral, primary TKA under spinal anesthesia were consecutively included in this prospective, observational study. Perioperative analgesia was standardized for all patients. Outcomes were postoperative pain during walk: from 6 to 24 hours (primary), from postoperative day (POD) 1 to 7 (secondary), and from POD 14 to 30 (tertiary). Two preoperative tonic heat stimuli with 47°C were used; short (5 seconds) and long (7 minutes) stimulation upon which patients rated their pain response on an electronic visual analog scale. Multivariate stepwise linear and logistic regressions analyses were carried out, including 8 potential preoperative explanatory variables (among these anxiety, depression, preoperative pain, and pain catastrophizing) to assess pain response to preoperative heat pain stimulation as an independent predictor for postoperative pain. A total of 100 patients were included, and 3 were later excluded. A weak correlation [rho (95% confidence interval); P value] was observed between pain from POD 1 to 7 and pain response to short [rho = 0.25(0.04 to 0.44); P = .02] and to long [rho = 0.27 (0.07 to 0.46); P = .01] heat pain stimulation. However, these positive correlations were not supported by the linear and logistic regression analyses, in which only anxiety, preoperative pain, and pain catastrophizing were significant explanatory variables (but with low R-squares; 0.05 to 0.08). Pain responses to 2 types of preoperative heat stimuli were not independent clinically relevant predictors for postoperative pain after TKA.