Phenotypic characteristics of joint fluid cells from patients with continuous joint effusion after total knee arthroplasty

Joint effusion after total joint arthroplasty (TJA) is a manifestation of inflammatory reactions within the prosthetic joint. Among the various causes for joint effusion following TJA, deep infection (DI), wear particle-induced synovitis (PS) and metal sensitivity to the implant should be excluded as soon as possible, as these may result in the failure of TJA. The present study analyzed joint fluid cells from patients after total knee arthroplasty (TKA) using fluorescence-activated cell sorter (FACS), and examined the feasibility of using FACS to exclude the possibility of biomaterial-related complication. A total of 72 TKAs from 64 patients suffering from joint effusion were examined in this study. Joint fluid was aspirated in outpatient clinics and applied to FACS. The results indicated that patients could be clearly classified into four types based on forward/side scatter profiles. Analysis of specific CD markers revealed that leukocytes were selectively recruited from blood to inflamed prosthetic joints. Dominant cell types were CD16+neutrophils in DI and increased rheumatoid activity, CD14+macrophages in PS, and CD3+CD45RO+T cells in metal sensitivity. These findings suggest the feasibility of diagnosing joint effusion by analyzing dominant cell type recruited using FACS. In conclusion, FACS may offer a useful tool for analyzing joint fluid cells from post-TJA patients and for excluding biomaterial-related complication following TJA.