Purpose: Total knee arthroplasty (TKA) is one of the most common and successful orthopaedic surgeries performed throughout the world. Although good pain relief can be achieved with TKA, significant proportion of patients experience persistent postsurgical pain (PPSP). A systematic review of recent studies from Europe and United States showed that 10-34% of patients complain of PPSP. However, since no prospective studies have ever been conducted in Japan, the prevalence of PPSP in the Japanese population is unknown. The aim of this prospective study was to elucidate the prevalence and preoperative risk factors of PPSP after TKA in a Japanese tertiary hospital. Methods: Between April 2012 to March 2018, patients were recruited in a Japanese tertiary hospital. Four hundred twenty-six TKAs were performed in patients during the period. Two hundred eighty-eight patients underwent unilateral TKA while 30 patients underwent simultaneous bilateral TKA. Preoperative diagnosis was osteoarthritis in 394 knees, rheumatoid arthritis in 28 knees, and osteonecrosis in 4 knees. Exclusion criteria were as follows: dementia, symptomatic venous thrombosis, periprosthetic join infection, and mal-positioned TKA (≧3 degrees error in sagittal and/or coronal plane). Preoperative evaluation included pain visual analog scale (VAS) at rest and at walk, WOMAC, Knee Society Score (KSS), EQ-5D, pain catastrophizing scale, pain DETECT. All TKA were performed under both general anesthesia and ultrasound-guided femoral nerve block. Postoperative pain was evaluated using a 100mm VAS. Patients were instructed to express their pain around the replaced knee while rest and walking during the past week by putting a mark on the 100mm VAS by themselves. PPSP was defined as a VAS score of >30 while walking at 1 year follow up. The prevalence of PPSP was calculated from patients followed at 1 year after surgery. The preoperative risk factors for PPSP were analyzed from patients who completed preoperative questionnaires. Statistical comparison between with and without PPSP was analyzed by Mann-Whitney U test and Chi-squared test. To determine the risk factors for PPSP, logistic regression analysis was used from among those factors which had significant difference (p<0.05) in univariate analysis. Results: Of 318 patients who underwent TKA, 346 knees of 254 patients were followed at 1 year after surgery. The prevalence of PPSP was 8.4% (19 of 346 knees). Two hundred and forty-six knees of 190 patients completed preoperative questionnaires. The mean age at surgery was 74 years old (range 43-90). Univariate analysis showed that patients with PPSP had significantly higher VAS at rest, WOMAC pain score, WOMAC stiffness score, WOMAC function score, WOMAC total score and lower EQ-5D compared with those without. Logistic regression analysis showed that WOMAC function score significantly affected PPSP (odds ratio = 1.078, 95% confidence interval 1.035-1.123). Conclusions: The rate of persistent pain was 8.4%. This result is lower than past reports from Europe and United States. In our department, surgeons basically take postoperative follow by themselves at 6 weeks, 3, 6, 12 months after surgery and every year. When we find patients who have something wrong around the replaced knee, we diagnose what is going on and treat appropriately. For example, we treated with steroid injection for infrapatellar saphenous neuralgia and pregabalin medication for lumber radiculopathy at some point. Recent studies have found that PPSP is associated with preoperative knee pain, younger patient, catastrophizing and mental health, while our findings showed the predictive factor of PPSP was WOMAC function score. This is the first report of prospective study for PPSP after TKA in Japan.Table 1.Comparison between patients with and without PPSP.PPSP (-) n=224 kneesPPSP (+) n=22 kneesP valueAge at surgery (years)73 [68-79]76 [72.5-79]0.116Sex (men/women)52 / 1723 / 190.304VAS at rest (mm)20 [5-40]30 [11.3-70]0.045VAS at walk (mm)20 [50-80]70 [54.8-80]0.295WOMAC pain9 [7-11]12 [10-13]0.001WOMAC stiffness5 [4-6]6 [4.3-6]0.036WOMAC function29 [20-39]41 [36.5-49]<0.001WOMAC total44 [32-56]60.5 [52.3-67.3]<0.001KSS knee score50 [39-61]50 [45-60]0.074KSS function score50 [45-60]45 [45-60]0.999EQ-5D0.631 [0.536-0.649]0.562 [0.495-0.596]0.002PCS27 [18.5-32]29.5 [18.8-33]0.243painDETECT10 [6-14]8 [7-16.5]0.946Data are median [IQR]. Statistical comparison between with and without PPSP was analyzed by Mann-Whitney U test and Chi-squared test. Open table in a new tab Data are median [IQR]. Statistical comparison between with and without PPSP was analyzed by Mann-Whitney U test and Chi-squared test.