Diagnosing Infection in “Dry” Prosthetic Joints

Despite a bevy of research and intense clinical focus, definitively diagnosing periprosthetic joint infections (PJIs) remains a major challenge in many patients. There is no single test that can confirm a PJI diagnosis with absolute accuracy, and surgeons often encounter clinical factors that make the diagnostic challenge even more complex. One such scenario is when a surgeon cannot aspirate enough fluid for culture from the affected joint of a patient who may have a PJI. In such situations, important microbiological data that would come from culturing synovial fluid are unavailable, leaving treating surgeons information-poor.

In the June 5, 2019 issue of The Journal, Li et al. provide surgeons with data about a controversial solution to this so-called “dry-tap” problem. The lead author performed aspirations on nearly 300 joints that were suspicious for periprosthetic infection. Eighty-two of those aspirations (29%) yielded ≤1.0 mL of synovial fluid. In those “dry-tap” cases, 10 mL of saline solution was injected into the joint, which was then reaspirated.

When comparing cultures from the aspirates that were the result of a saline lavage to those in which no lavage was performed, the authors found overlapping 95% confidence intervals in sensitivity, specificity, positive predictive value (PPV), and negative predictive value. However, the specificity (0.991 vs 0.857) and PPV (0.987 vs 0.889) were higher in the nonlavage cohort, even if those differences did not reach statistical significance. In addition, no significant differences were found between the groups in terms of relative frequencies of specific pathogen types.

Although the authors conclude that this lavage-and-reaspiration technique “is not necessarily inappropriate,” it is important to note that no post-hoc power analysis was performed, and therefore type II error needs to be considered because the study was probably underpowered. In addition, the International Consensus Meeting (ICM) recommends against lavaging a “dry” joint to obtain fluid for culture, largely because the injected saline will dilute results if a leukocyte esterase strip test or cell count is subsequently performed as part of the PJI-diagnosis process. Still, the authors point out that the data supporting the ICM’s recommendations against this practice are relatively weak, and the specificity and sensitivity data from this study are quite satisfactory.

So does this give us another option for determining whether a periprosthetic joint infection is present in patients from whom little or no synovial fluid can be obtained? Maybe. But this technique requires further investigation before it becomes widely implemented in practice. Without validation, it risks becoming just one more variable that could reinforce our own confirmation biases in these challenging cases. With further validation, however, it could allow pre-revision collection of valuable and accurate culture information from “dry” joints.

Chad A. Krueger, MD
JBJS Deputy Editor for Social Media

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