Flow cytometry as a diagnostic tool for identifying total hip arthroplasty loosening and differentiating between septic and aseptic cases.

Purpose: Implant loosening represents one of the major factors of total hip arthroplasty (THA) failure. The purpose of this study was to identify specific markers indicative of septic and aseptic loosening in patients that underwent THA.

Methods: Flow cytometry was performed in blood samples of 20 patients with loosening (10 septic/10 aseptic). Additional ten healthy individuals served as a control group. The expression of surface receptors and cytoplasmic molecules in patients that underwent THA was quantified. CD62L, CD18, CD11a, CD11b and CD11c expressions were evaluated and correlated with the presence of loosening. Also, a comparison between septic and aseptic THA loosening characteristics was performed.

Results: The mean fluorescence intensity (MFI) for CD18 was significantly decreased on all leukocytes subsets in both septic and aseptic loosening compared to control group (p < 0.005 in all occasions). Patients with aseptic loosening showed increased MFI for CD11b in granulocytes and for CD11c in monocytes and granulocytes compared to the control and aseptic group (p = 0.02 and p = 0.005, respectively). In patients with septic loosening, an increase in MFI for CD11c was observed in monocytes only compared to control group (p = 0.03). The comparison between aseptic and septic loosening showed significantly lower CD18 MFI value in granulocytes for aseptic loosening (p = 0.008).

Conclusions: CD11 and CD18 MFI values appear to be indicative of loosening in THAs. Flow cytometry markers can be used to identify THA loosening, as well as to differentiate between septic and aseptic cases.