Summary

Our results indicate that acute postoperative pain after TKA is an independent risk factor for chronic postoperative pain at 1 year postoperatively, and the optimal cut-off value for acute postoperative pain at rest is 37.7 mm of VAS score.

Abstract

Purpose

The purpose of this study was to examine risk factors for chronic postoperative pain (CPSP) after TKA and to determine whether postoperative acute postoperative pain (APSP) is associated with CPSP.

Methods

A retrospective observational study of patients undergoing unilateral primary total knee arthroplasty (TKA) was conducted at a single university hospital. All patients received the same standardized postoperative pain management and rehabilitation. The 100mm scale visual analogue scale (VAS) score was adopted for the evaluation of the pain scale. For an evaluation of APSP, the VAS score at rest was defined as the mean value measured periodically from the following day to three days after TKA at 6:00 AM, 12:00 PM, and 8:00 PM. For an evaluation of CPSP, the VAS score at rest and during activity were evaluated at 1 year postoperatively, and the presence of CPSP was defined as VAS at rest or during activity of 30 mm or greater.

Results

A total of 263 patients were analyzed and 39 patients (14.8%) were in the CPSP group and 224 patients were in the non-CPSP group. In addition, 51.3% of patients in the CPSP group were dissatisfied compared to 2.6% of patients in the non-CPSP group. The multivariable logistic regression analysis revealed that the APSP at rest was the independent risk factor associated with CPSP (OR = 1.04; 95% CI = 1.01 to 1.08; p = 0.025). The optimal cut-off values of APSP at rest for CPSP were 37.7 (AUC = 0.766, 95% CI = 0.699-0.834).

Conclusion

APSP at rest is an independent risk factor associated with CPSP after TKA and the cut-off value of APSP at rest was a VAS score of 37.7mm.