The incidence of infection remains 1–2% after primary total joint arthroplasty and even higher after revision procedures in spite of advances in prophylactic antibiotics and clean air operating theatre environment. Detection of low-grade infection in a prosthetic joint can often be very difficult. None of the investigations available so far have 100% sensitivity and specificity. This has huge implications on the subsequent treatment, cost and patient morbidity. Revision of an unrecognized 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. We prospectively assessed 70 patients undergoing revision arthroplasty (57 hips and 13 knees). Each patient was pre operatively assessed clinically and radiologically. ESR and CRP results were noted. During revision, synovial fluid and tissue cultures from capsule, bone and bone-cement interface were obtained. None of the patients received pre or intra operative antibiotics till the specimens were taken. Standard microbiology and histology study were done on tissue samples. In addition Polymerase Chain Reaction study was done on the synovial fluid. In this method, DNA is extracted from the bacterial cell, it is polymerized 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 intraoperative findings, tissue culture and histology results and a period of post operative follow up (12 months to 36 months). Six (8%) of the 70 cases that had revision arthroplasty were clinically infected. Polymerase chain reaction was positive in 25 cases, tissue cultures were positive in 5 cases and histology was positive in 5 cases for infection. PCR showed sensitivity and specificity of 83% and 69% respectively. Tissue culture showed sensitivity and specificity of 83% and 100% respectively. Histology showed sensitivity and specificity of 83% and 100% respectively. 20 out of 25 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 that can be detected by ultrasonication of implant and immunofluorescence methods. PCR is more sensitive in detection of bacterial DNA. However it has low specificity and combination of tissue cultures and histology can still provide a reliable diagnosis of infection.
