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目的:探讨初次全膝关节置换术后关节液白细胞（white blood cell，WBC）计数和多形核细胞（polymorphonuclear cells，PMN）比例的变化趋势及其临床意义。方法:纳入2021年4月至2021年7月接受初次全膝关节置换术的59例（92膝）患者，男13例（20膝）、女46例（72膝），年龄（65.17±7.49）岁（范围48~79岁），体质指数（27.64±3.74）kg/mn 2（范围17~36 kg/mn 2）。单膝26例，双膝33例；左侧46膝，右侧46膝；诊断为骨关节炎54例（84膝），类风湿关节炎5例（8膝）。患者住院后均未使用抗生素，术前30 min、术后预防性使用抗生素。检测术中（反映术前正常水平）、术后第2、5和35天关节液WBC计数和PMN比例，分析其变化规律。术中取切开关节囊后未混血的关节液，术后第2、5和35天以髌骨外上缘为穿刺点抽取关节液。研究终点为诊断为急性假体周围感染或未发生假体周围感染的患者完成90 d的随访。n 结果:术后关节液WBC计数和PMN比例呈先升高后下降的趋势。术前、术后第2天、第5天、第35天关节液WBC计数分别为0.222（0.100，0.567）×10n 9/L、20.011（14.573，29.129）×10n 9/L、6.080（3.676，8.797）×10n 9/L、0.533（0.394，0.749）×10n 9/L，手术前后的差异有统计学意义（χn 2=247.34，n P<0.001）；关节液PMN比例分别为19.9%（15.0%，30.0%）、96.0%（95.0%，97.0%）、91.0%（89.0%，93.0%）、20.5%（15.6%，26.9%），手术前后的差异有统计学意义（χn 2=242.52，n P0.05），其他时间点的差异均有统计学意义（n P<0.05）。n 结论:全膝关节置换术后关节液WBC计数和PMN比例短期内快速升高，然后以不同速率下降至术前水平。急性应激期（术后5 d内）参考肌肉与骨骼感染协会推荐阈值诊断感染可造成假阳性；术后第35天恢复至术前水平可作为排除早期感染的依据，关节液PMN比例可能比WBC计数更具诊断价值。“,”Objective:To investigate the changes and clinical significance of white blood cell (WBC) count and polymorphonuclear cells (PMN) proportion of synovial fluid after primary total knee arthroplasty (TKA).Methods:A total of 59 patients (92 knees) who underwent TKA from April 2021 to July 2021 were included, including 13 males (20 knees) and 46 females (72 knees). The patients were with average age 65.17±7.49 years old (range 48-79) and with body mass index (BMI) 27.64±3.74 kg/mn 2 (range 17-36 kg/mn 2). There were 26 cases involved lateral knee and 33 cases bilateral knees. The left knee was involved in 46 knees, while other 46 were involved in right side. There were 54 patients diagnosed as osteoarthritis (84 knees) and 5 as rheumatoid arthritis (8 knees). None of the patients received antibiotics after hospitalization. Antibiotics were used prophylactically 30 min before surgery and after surgery. The synovial fluid WBC count and PMN proportion were detected during operation (It reflects the normal preoperative level) and on the 2nd, 5th and 35th day after operation. The changes of these indexes were analyzed. The unmixed synovial fluid was collected after the incision of the joint capsule during the operation. The outer upper edge of the patella was taken as the puncture point to extract the synovial fluid on the 2nd, 5th and 35th days after the operation. The final follow-up end point was a diagnosis of acute periprothetic joint infection (PJI) or 90 days of follow-up for patients without PJI.n Results:After operation, the synovial fluid WBC count and PMN proportion showed a trend of increasing and then decreasing. The synovial fluid WBC count were 0.222(0.100, 0.567)×10n 9/L, 20.011(14.573, 29.129)×10n 9/L, 6.080(3.676, 8.797)×10n 9/L, 0.533(0.394, 0.749)×10n 9/L before surgery and at 2nd, 5th and 35th day after surgery respectively. The difference before and after operation was statistically significant (χn 2=247.343, n P<0.001). The synovial fluid PMN proportion were 19.9%(15.0%, 30.0%), 96.0%(95.0%, 97.0%), 91.0%(89.0%, 93.0%) and 20.5%(15.6%, 26.9%) respectively and with significant difference (χn 2=242.521, n P0.05). However, the differences compared with that at other time points were statistically significant (n P<0.05).n Conclusion:The synovial fluid WBC count and PMN proportion increased rapidly in the short term after TKA and then decreased to the preoperative level at varied rates. Referring to the Musculoskeletal Infection Society (MSIS) recommended threshold for diagnosing infection during the acute stress period (within 5 d postoperatively) can result in false positives. Recovery to preoperative levels at 35th days postoperatively can be used as a basis for ruling out early infection. Thus, early joint fluid PMN proportion may have more diagnostic value than WBC counts.