The aim of this study was to evaluate the usefulness of the intra-operative synovial fluid culture and post-operative suction drainage tip culture as a method for predicting the development of a deep infection after primary TKA.

Between July 1998 and July 2002, 324 primary total knee arthroplasty procedures were performed and aerobic and anaerobic bacterial cultures for intra-operative synovial fluid and post-operative suction drainage tip were obtained. The results of culture of intra-operative synovial fluid and post-operative suction drainage tip of total 324 primary TKA cases were analyzed. The sensitivity, specificity and predictive value were calculated. positive culture rate for osteoarthritis was compared with rheumatoid arthritis and the results of a single TKA was compared with both simultaneous TKA.

14 out of 324 knees showed a positive intra-operative synovial fluid culture and 10 cases showed a positive post-operative suction drainage tip culture. Only 1 case out of the 4 deep infection cases showed a positive on suction drainage tip culture with S. aureus being isolated. The specificity of the intra-operative synovial culture was 95.6% and the negative predictive value was 98.7%. The sensitivity of the post-operative suction drainage tip culture was 25%, the specificity was 97%, the positive predictive value was 10% and the negative predictive value was 99%. The positive culture rate was similar in the osteoarthritis and rheumatoid arthritis cases (respectively p=0.4717, p=0.6550). However, the culture positive rate between single and both simultaneous TKA was numerically different, approximately 2 times (3.2% vs 6.31% for intra-operative synovial culture and 4.0% vs 9.47% for post-operative suction drainage tip culture) but it was not statistically significant (respectively p=0.311, p=0.1051).

In primary TKA, a culture of intra-operative synovial fluid and post-operative suction drainage tip cannot predict a postoperative deep wound infection. It is recommended that careful observation for other signs of a deep infection be examined when a clinically significant true pathogen isisolated.