Tag Archive | culture

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

Use Data, Guidelines, and Intuition to Manage Infection after Toe/Forefoot Amputation

Osteomyelitis for OBuzzThe number of articles published each year in orthopaedics that evaluate infections seems to approach, if not exceed, 1,000. Yet, despite all of these publications, consensus statements, and guidelines, we seem to have very few concrete recommendations about which every surgeon will say, “This is what needs to be done.” So we send out samples, run cultures, sonicate implants, and sometimes even perform DNA sequencing, and then we mix the data with selected recommendations and intuition to make our final treatment decisions. Foolproof? No, but it is the best we can do in many situations.

The article by Mijuskovic et al. in the September 5, 2018 edition of The Journal helps simplify this type of decision making in the setting of residual osteomyelitis after toe or forefoot amputation. The authors evaluated 51 consecutive patients with gangrene and/or infection who underwent either digit or partial foot amputations. They found that, after surgery, 41% of the patients without histological evidence of osteomyelitis (which the authors considered the reference, “true positive” analysis) had a positive culture from the same sample.  In addition, only 12 patients (24%) had both positive histological findings and positive cultures, the criteria set forth by the Infectious Disease Society of America for the definitive diagnosis of osteomyelitis.

As interesting as the main findings of the study are, some of the “minor” results are even more curious.  The decision regarding which patients received antibiotics after amputation seemed largely arbitrary, with 10 of the 14 patients who had a positive histological result not receiving any postoperative antibiotics. (Five of those patients ended up needing a secondary procedure.) In addition, because of the need for decalcification prior to analysis, the median time to receiving histological results was almost a week. Based on the findings in this study, in many instances patients are sent home or to a rehabilitation facility with antibiotics based only on the results of a potentially “false-positive” culture.

The authors conclude that their results “cast doubt on the strategy of relying solely on culture of bone biopsy specimens when deciding whether antibiotic treatment for osteomyelitis is necessary after toe or forefoot amputation.” But this paper also highlights the fact that we are still looking for definitive answers about which data to use and which to disregard when it comes to the detection and treatment of post-amputation osteomyelitis. We surgeons decide on which side to err, and we need to appreciate all three facets—data, guidelines, and patient factors—when discussing treatment options with patients.

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

Whence P. Acnes in Shoulder Arthroplasty?

p-acnes-pie-chartPropionibacterium acnes is a frequently isolated pathogen in postoperative shoulder infections, but where exactly does it come from? According to a study by Falconer et al. in the October 19, 2016 Journal of Bone & Joint Surgery, P. acnes derives from the subdermal edges of the surgical incision and spreads through contact with the surgeon’s gloves and surgical instruments.

The authors obtained specimens for microbiological analysis at five different sites from 40 patients undergoing primary shoulder arthroplasty. Thirty-three percent of the patients had at least one culture specimen positive for P. acnes, and the most common site of P. acnes growth was the subdermal layer, followed by forceps.

The authors observed no clinical postoperative infections during the follow-up of 6 to 18 months, although that is a relatively short investigation period for a pathogen that often causes late-onset indolent infections. The authors conclude that “it is likely that surgeon handling of the skin and subdermal layer contaminates the rest of the surgical field.” Although the study did not investigate preventive techniques, based on the findings the authors suggest the following possible prophylactic approaches:

  • Minimizing handling of the subdermal layer
  • Changing gloves after the dermis is cut
  • Avoiding contact between implants and the subdermal layer
  • Repeating use of antibacterial agents once the wound is opened