Synovitis after Total Knee Arthroplasty: Possible Cause of Residual Postoperative Pain (Preliminary Study)

Abstract

Purpose: The cause of residual pain after total knee arthroplasty (TKA) was unknown. Little attention has been given to postoperative synovitis as a cause of unexplained residual pain after TKA. Here we preliminarily investigated the relationship between synovitis after TKA and pain with ultrasonography. Methods: This study was conducted using convenient outpatient samples followed for TKA. Synovitis was accessed with ultrasonography. We originally made synovitis scores, which are a summation of the synovitis grade in the entire knee. Pain assessments including rest, moving pain visual analog scale (VAS) and WOMAC score and its subscale were evaluated. Correlations between synovitis scores or the maximum grade and pain assessments were analyzed. Pressure pain thresholds (PPTs) on synovitis were evaluated. Results: 46 knees in 37 patients (34 female, 3 male) were evaluated. Synovitis scores correlated with rest and moving VAS (r = 0.439; 0.355, p = 0.002, 0.016). PPTs on positive synovitis significantly decreased compared with grade zero (average PPTs (SD) on grade zero, one, two = 484(21), 255(13), 268(20) kPa; p < 0.001). Conclusion: Synovitis after TKA was associated with residual unexplained pain. Ultrasonography and synovitis scores should be available to evaluate synovitis after TKA.