Source: Chest  |  Posted 4 years ago

By Jill Stein

SAN DIEGO, CA -- February 16, 2007 -- Synovial fluid cell count is the best perioperative testing modality for identifying the presence of periprosthetic sepsis at the site of a total knee arthroplasty (TKA), researchers reported here at the 2007 Annual Meeting of the American Academy of Orthopedic Surgeons (AAOS).

The findings were presented here on February 16[^]th[] by Craig J. Della Valle, MD, assistant professor, department of orthopaedic surgery, Rush University Medical Center, orthopaedic surgeon, Oak Park Hospital, joint reconstruction specialist, Midwest Orthopaedics at Rush, Chicago, Illinois.

In their study, Dr. Della Valle and colleagues evaluated the usefulness of widely available tests for determining periprosthetic infection.

Infection must always be investigated as a potential cause of failure in the patient undergoing revision TKA because the treatment of patients with an infection is fundamentally different from the treatment of patients whose failure is not caused by an infection, Dr. Della Valle pointed out.

However, while there is a multitude of tests available for diagnosing infection at the site of TKA, few studies have used a consistent algorithm to determine the utility of the various tests.

Dr. Della Valle and his team evaluated 105 consecutive knees in 94 patients who underwent perioperative evaluation and revision surgery by a single surgeon.

The following values were considered consistent with infection: erythrocyte sedimentation rate greater than 30 mm/hr, C reactive protein greater 10 mg/dL, an average polymorphonucleocytes (PMN) per high power field level greater than 10 on histopathologic examination, a synovial fluid cell count greater than 3,000 WBC/mL and a cell count differential greater than 65% PMN.

Three sets of intraoperative cultures were obtained in all cases, including aerobic, anaerobic, acid-fast bacillus, and fungal cultures.

An individual case was judged to be infected if an organism grew on solid media from at least 2 of the 3 intraoperative cultures or if 2 of the following 3 criteria were met: at least 1 positive culture from the solid media; final pathology consistent with infection; gross infection at the time of surgery.

Eleven of the 105 cases were excluded for various reasons. Forty-one of the remaining 94 cases were judged to be infected.

Results showed that the synovial fluid cell count had the highest sensitivity (100%), specificity (98%), positive predictive value (97.6%), negative predictive value (100%), and accuracy (98.9%).

"Based on our results, we believe perioperative aspiration with a cell count (using a threshold of > 3,000 WBC/mL) to be the best test for diagnosing infection at the site of a failed TKA," Dr. Della Valle said.

Advantages of this test include the ability to perform it either pre- or intraoperatively, its low cost, and "ubiquitous nature," he added. Also, the test is easy to perform in an office setting and can potentially identify the infecting organism to assist with postoperative antibiotic management.

[Presentation title: Perioperative Testing for Sepsis in Revision Total Knee Arthroplasty. Abstract P140]