Sunday, November 13, 2016

Revision arthroplasty - is there a reason to perform a pre-revision tissue biopsy useful to predict culture results at surgery?

Utility of prerevision tissue biopsy sample to predict revision shoulder arthroplasty culture results in at-risk patients.

These authors  evaluated the utility of a prerevision biopsy sample in predicting positive cultures or a final diagnosis of infection in the setting of an "at-risk" failed shoulder arthroplasty in 77 patients with no history of infection undergoing revision shoulder arthroplasty.

All patients with a painful arthroplasty underwent laboratory evaluation, including ESR and CRP, as well as a fluoroscopically guided intra-articular aspiration (cultures were held for 2 weeks). Patients were classified into 1 of 4 categories, and prerevision biopsy was performed according to the grouping: (1) gross purulence, drainage, fluctuance, a sinus tract or a positive aspirate (bacterial growth on culture), (2) ESR and CRP were normal and the aspiration had no growth, (3) results for ESR or the CRP, or both, were abnormal, with no growth on the aspiration, and (4) results for ESR and CRP were normal and no fluid was available on the aspirate.

Group 1 patients were considered infected; therefore, revision arthroplasty was performed consisting of explantation and placement of an antibiotic-impregnated cement hemiarthroplasty or a resection arthroplasty without performing a prerevision biopsy. Group 2 patients were considered at low risk for infection; therefore, revision arthroplasty was performed without performing a prerevision biopsy. Group 3 and 4 patients were considered “at-risk” for the presence of infection at definitive revision; therefore, pre revision open or arthroscopic biopsies were performed in these groups. This study evaluated the 17 patients treated in groups 3 and 4 that had a pre revision biopsy.

All cultures were assessed for aerobic and anaerobic bacteria held for 2 weeks with specific instructions to rule out P acnes. A minimum of 2 samples (3 samples for the final 15 patients) were taken for culture at the time of the biopsy and also at the time of revision arthroplasty.

2 out of 9 patients with positive biopsy cultures had negative cultures at revision.
3 out of 6 patients with negative biopsy cultures had positive cultures at revision.

The samples from 11 of 17 biopsy procedures were positive for at least 1 culture. Bacteria included
P acnes in 8, coagulase-negative Staphylococcus in 2, Streptococcus mitis in 1, diphtheroid in 1, and Brevibacterium casei in 1. Multiple bacteria grew in the samples from 2 patients.

At the time of revision, 12 of 17 patients had cultures return positive for at least 1 culture. Bacteria included P acnes in 7, coagulase-negative Staphylococcus 2, S lugdunensis in 1, and Enterococcus faecium in 1.

Two of 9 patients who had positive cultures from the biopsy and the revision had different bacteria on the revision culture compared with the biopsy! (see yesterday's post).

Comment: This paper provides some important insight into the difficult challenge of predicting the culture results at the time of revision surgery based on preoperative information. First of all it is of note that the authors did pretty well at predicting culture positivity at revision based on clinical criteria alone: 12 of the 17 patients that they determined were 'at risk' indeed had positive cultures at revision without submitting them to an additional surgical procedure.

Of particular interest is their Group 4 in which the results for ESR and CRP were normal and no fluid was available on the aspirate. 4 of the 7 shoulders were culture positive at revision even though there were no pre-revision abnormal labs. Only 2 of these 4 had positive biopsies.

What is missing from this report is the results of the cultures at revision surgery for Group 2: ESR and CRP were normal and the aspiration had no growth. There is substantial evidence that there is a very high rate of false negative joint fluid cultures in the presence of multiply positive tissue and explant cultures. We wonder what percent of these 'fluid no growth' cases had positive cultures at revision surgery.

In our practice we do not submit patients to an additional surgical procedure to obtain a biopsy before revision of a failed shoulder arthroplasty because, as this paper demonstrates, a negative biopsy does not exclude the possibility of positive cultures at the time of revision. This is because bacteria are not evenly distributed through a culture-positive shoulder. 

As an analogy, we could take a number of samples of this lawn and not find two that show a mushroom, but that doesn't mean mushrooms are not really there.

The reader is directed to two recent related posts:

The challenge of diagnosing a propionibacterium "infection"