Changing of white blood cell count and proportion of polymorphonuclear cells of synovial fluid in total knee arthroplasty patients before and after operation / 中华骨科杂志

ABSTRACT

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/m 2 (range 17-36 kg/m 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. 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)×10 9/L, 20.011(14.573, 29.129)×10 9/L, 6.080(3.676, 8.797)×10 9/L, 0.533(0.394, 0.749)×10 9/L before surgery and at 2nd, 5th and 35th day after surgery respectively. The difference before and after operation was statistically significant (χ 2=247.343, 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 (χ 2=242.521, P<0.001). Pairwise comparison of synovial fluid WBC count and PMN proportion before and on day 35 indicated no statistical significance ( P>0.05). However, the differences compared with that at other time points were statistically significant ( P<0.05). 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.