Investigation of association between the preoperative intra-articular anesthetic test and persistent pain after total knee arthroplasty.

Background: A better understanding of the etiology of persistent pain after total knee arthroplasty (TKA) is required to prevent unfavorable outcomes. The purpose of this study was to investigate the association of persistent pain after TKA, patient characteristics, and the remaining pain ratio per the preoperative intra-articular anesthetic test.

Methods: This study included 89 patients who underwent TKA and underwent an intra-articular anesthetic test preoperatively. The remaining pain ratio out of 100 percent 30 min after intra-articular anesthetic injection and demographic data were also evaluated preoperatively. Numerical rating scale (NRS) scores for pain during movement (Q1), at rest (Q2), at first movement in the morning (Q3), and during climbing up and down stairs (Q4) were evaluated 1 year after TKA. Multiple linear regression analysis was performed to assess the impact of independent variables on the NRS score for questionnaire No.4. and the remaining pain ratio per the intra-articular anesthetic.

Results: The mean remaining pain ratio per the preoperative intra-articular anesthetic test was 29.3%. The NRS score for Q4 was significantly higher than those for any of the other NRS questionnaires administered 1 year after TKA (Q1-Q4, Q2-Q4, P < 0.001; Q3-Q4, P < 0.05). The analysis found the weak correlation between the pain ratio of anesthetic test and the NRS score for Q4 after TKA (R = 0.28, P = 0.018). BMI and preoperative FTA were the major predictors of remaining pain ratio per the intra-articular anesthetic test (R = 0.40, P = 0.002).

Conclusion: This study revealed that the remaining pain ratio per the preoperative intra-articular anesthetic test was weakly correlated with persistent pain during climbing up and down stairs 1 year after TKA. In addition, BMI and preoperative FTA were associated with the remaining pain ratio per the preoperative intra-articular anesthetic test.