Standard and newer testing methods may aid detection of joint infection

Denis Nam

Denis Nam, MD, MSc, discussed some strategies to diagnose a periprosthetic infection following total joint arthroplasty, including newer tests that have been introduced, at the American Association of Hip and Knee Surgeons Annual Meeting.

Nam noted patients who present with a painful joint should be considered infected until infection is ruled out.

“Always have a high index of suspicion. There are signs and symptoms that can be concerning, including wound drainage, a return to the OR after surgery or any other risk factors such as immunosuppression,” he said.

For initial workup, Nam noted surgeons should first review erythrocyte sedimentation rate and C-reactive protein levels, and to aspirate the joint if the levels are elevated, focusing on synovial white blood cell count, polymorphonuclear differential and culture.

Role of imaging

“Regarding imaging modalities, radiographs are rarely diagnostic, but you can sometimes see early loosening or osteolysis that is concerning,” Nam said.

Nuclear medicine tests are second-line modalities with weak clinical practice guideline recommendations. MRI and CT should not be used to diagnose infection, according to Nam. He noted that gram stains are not recommended because they can provide false positives and the dye used may itself contain bacteria.

Antibiotics should be held until the surgeon aspirates the joint and obtains cultures, Nam said.

“It may have an unclear impact on [erythrocyte sedimentation rate] ESR and CRP in your synovial white cell count, but antibiotics clearly affect your culture results,” he said. “You can get culture negative infections and once you get a culture negative infection, it is much harder to treat that infection and tailor a specific antibiotic regimen.”

D-dimer testing

Some newer tests may be helpful in diagnosing infection, according to Nam. One prior study has shown a serum D-dimer test to have higher sensitivity and specificity in diagnosing septic revisions compared with ESR and CRP, while leukocyte esterase strip testing has been found to have high specificity in diagnosing septic TJAs.

“[Leukocyte esterase] is simple, it is inexpensive; however, it is important to note that sometimes it can be difficult to measure if you aspirate bloody fluid,” Nam said. “A larger body of research is necessary to determine the utility of routinely using D-dimer and leukocyte esterase testing to diagnose infection.”

Although studies have shown there is high sensitivity and specificity when synovial CRP is used to diagnose infection, one other study has questioned its utility vs. a serum CRP measurement, according to Nam.

Alpha defensin as an adjunct test

Furthermore, alpha defensin has also shown mixed results with regard to sensitivity and specificity, but it may be a useful adjunct with other tests, he said.

“[Alpha defensin] can outperform leukocyte esterase. It is sensitive to a wide spectrum of organisms and perhaps most useful is that it has been found to still be effective even in the setting of prior antibiotics,” Nam said.

Despite the existing uncertainty regarding when it would be most beneficial to use these additional tests, Nam noted that using a step-wise approach is critical.

“Get serum testing. If you have a suspicious exam or history, aspirate the joint. Move on to intraoperative tests if necessary,” Nam said. “There are no perfect sets of tests, but, clearly, we have more tests at our disposal.” – by Casey Tingle

Reference:

Nam D. Diagnosis of periprosthetic infection – an update on the available techniques, controversies and definitions. Presented at: American Association of Hip and Knee Surgeons Annual Meeting; Nov. 1-4, 2018; Dallas.

For more information:

Denis Nam, MD, MSc, can be reached at Rush University Medical Center, 1653 W. Congress Pkwy, Chicago, IL 60612; email: denis.nam@rushortho.com.

Disclosure: Nam reports he is a paid consultant for KCI, Stryker and Zimmer Biomet; and receives research support from KCI and Zimmer Biomet.