Introduction: Infection constitutes a serious complication of joint arthroplasty, with an incidence of 1–2% after primary arthroplasty and even higher after revision procedures. Detection of low-grade infection in a prosthetic joint can often be very difficult, with huge implications on the subsequent treatment, cost and patient morbidity. Revision of an unrecognised infected arthroplasty may lead to less satisfactory results in a high proportion of cases. We utilized Polymerase Chain Reaction, a molecular biology technique to detect bacterial DNA from the synovial fluid of patients undergoing revision surgery, in comparison with conventional infection detection techniques.
Methods: We prospectively assessed 81 patients undergoing revision arthroplasty (67 hips and 14 knees). Each patient was pre-operatively assessed clinically and radiologically. ESR and CRP results were noted. During revision, synovial fluid and tissue cultures were obtained and antibiotics were given only after the specimens were taken. Standard microbiology and histology study were done on tissue samples. In addition Polymerase Chain Reaction study was performed on the synovial fluid. In this method, DNA is extracted from the bacterial cell; it is polymerised and finally visualized by gel electrophoresis. Post-operatively patients were followed up at regular intervals. Diagnosis of infection included correlation between clinical, radiological and laboratory investigations along with intra-operative findings, tissue culture and histology results and a period of postoperative follow up of 12 to 36 months.
Results: Eleven (13.58%) of the 81 cases that had revision arthroplasty were clinically infected. Polymerase chain reaction was positive in 30 cases, tissue cultures were positive in 8 cases and histology was positive in 10 cases for infection. PCR showed sensitivity and specificity of 0.92 and 0.72 respectively. Tissue culture showed sensitivity and specificity of 0.72 and 0.81 respectively. Histology showed sensitivity and specificity of 0.9 and 1 respectively.
Discussion: Twenty out of 30 PCR positive cases did not show any clinical evidence of infection. It is unclear whether this represents contamination during surgery or in the PCR lab. Alternatively this may represent true positive PCR results in cases with low bacterial count or bacteria growing within a biofilm that can be detected only by ultrasonication of the implant and immunofluorescence methods. PCR could also be detecting non-culturable forms of bacteria or bacterial fragments.
Conclusion: PCR has high sensitivity and low specificity for detection of bacterial DNA. The combination of tissue cultures and histology can still provide a reliable diagnosis of infection.
