The pathogenesis of osteolysis in failed total hip arthroplasty is not fully understood. The purpose of this study is to identify CD4+CD25+ Regulatory T cells in periprosthetic tissues in failed total hip replacements secondary to osteolysis. Intra-operative tissue samples and peripheral blood were collected from patients undergoing revision total hip arthroplasty surgery. Regulatory T cells were present in the tissues, and significantly increased in the peripheral blood in patients with failed total hips compared to normal controls. Further characterization of these regulatory T cells are warranted as they may play a role in osteolysis in loose total hip replacements.

Osteolysis remains the most common complication following total joint arthroplasty. To date, no authors have investigated the role of CD4+CD25+ regulatory T cells (T_REG) participating in the osteolytic pathogenesis. The purpose of this study is to quantitate the presence of T_REG cells in periprosthetic tissues in failed total hip replacements secondary to osteolysis.

Fifteen consecutive patients booked for revision total hip arthroplasty secondary to osteolysis were included. Tissue samples were collected: peripheral blood (PB), synovial fluid (SF), synovial tissue (ST), and interface tissue (IT) between the failed component and the bone defect. Total lymphocytes were isolated and analyzed using fluorescent-tagged antibody cell sorting (FACS) for the presence of T_REG cells. Frozen sections of ST and IT were analyzed with immunohistochemistry for T_REG cells.

T_REG cells were significantly upregulated (p< 0.01) in the PB (68%) of revision hip patients compared to normal controls PB (44%). In the synovial tissue (ST) and interface tissue (IT), 57% of the lymphocytes isolated were TREG cells. The presence of T_REG cells in the ST and IT were confirmed with immunohistochemistry.

T_REG cells are upregulated in the peripheral blood of patients with failed total hips secondary to osteolysis. The TREG cells are also present in the synovial tissue and interface tissue.

Evidence for involvement of regulatory T cells contribute to our understanding of this complex biologic response to artificial wear particles.

Functional studies of these T_REG cells are warranted as they are upregulated in patients with loose total hip replacements.

Purpose: The gold standard for treatment of infected total hip or knee replacements remains a 2-stage exchange arthroplasty. This includes aggressive irrigation and debridement, implant removal, insertion of antibiotic impregnated spacers, iv antibiotics, and eventual reimplantion with a definitive prosthesis. The purpose of this study was to quantify Vancomycin and Gentamycin synovial fluid levels at the time of reimplantation following a 2-stage exchange arthroplasty for a infected total hip or knee replacements.

Methods: The senior author performed 42 two-stage reconstructions using the prosthesis of antibiotic-loaded acrylic cement (PROSTALAC). Each 40g bag of Pala-cos-R cement was impregnated with Vancomycin 2g, Gentamycin 4.8g, and plus/minus ancef 2.0g (depending on penicillin allergy). At the time of reimplantation, the synovial fluid was immediately analyzed for levels of Vancomycin and Gentamycin.

Results: 17 patients were taken for stage II within 60 days (avg. 53). The synovial fluid vancomycin and gentamycin levels were 12.7 and 20.6 respectively. Twelve patients had stage II between 60 and 90 days (avg. 79). The synovial fluid vancomycin and gentamycin levels were 6.2 and 14.9 respectively. The remaining 13 patients underwent stage II beyond 90 days (avg. 192), and their synovial fluid vancomycin and gentamycin levels were 3.3 and 2.4 respectively. 40 of 42 patients had their infections eradicated.

Conclusions: in vitro evidence predicts that antibiotics elute rapidly from bone cement. The results of this study confirm that substantial doses of vancomycin, gentamycin, and ancef per bag of Palacos-R cement does confer long term synovial fluid antibiotic levels well above the minimal inhibitory concentrations required to treat infected total joints. When stage II reimplantation is done at greater than 3 months, synovial fluid antibiotic levels decline significantly.