Monday, December 26, 2016

Failed shoulder joint replacement: single stage revision when cultures are positive for Propionibacterium

Single-Stage Revision Is Effective for Failed Shoulder Arthroplasty with Positive Cultures for Propionibacterium

These authors point out that cultures taken at the tim of revision shoulder arthroplasty are often positive for Propionibacterium.  They tested the hypothesis that the functional outcomes of revising Propionibacterium culture-positive failed arthroplasties with a single-stage revision and immediate antibiotic therapy are not inferior to the clinical outcomes of revising failed shoulder arthroplasties that are not culture-positive.

Fifty-five shoulders without obvious clinical evidence of infection had a single-stage revision arthroplasty. Specifically all components (humeral and glenoid) were removed, a thorough debridement was carried out and a new humeral hemiarthroplasty was inserted with Vancomycin impregnated allograft. The residual glenoid bone was smoothed, but not bone grafted. No glenoid components were replaced.

Preoperative antibiotics were withheld until culture specimens were taken; a minimum of 5 tissue or explant specimens were obtained from each shoulder. Specimens were cultured for 21 days on blood agar (trypticase soy agar with 5% sheep blood), chocolate agar, Brucella agar (with blood, hemin, and vitamin K), and brain-heart infusion broth. Bacteria that were isolated received a full species-level identification by means of 16S rDNA sequencing.

After all culture specimens were obtained, 15 mg/kg of vancomycin and 2 g of ceftriaxone were administered intravenously. Patients were continued on antibiotics until the results of the cultures were finalized. Two or more cultures became positive, the infectious disease service started intravenous ceftriaxone and/or vancomycin through a PICC line with oral rifampin for 6 weeks followed by oral antibiotics in the form of amoxicillin and clavulanate or doxycycline for a minimum of 6months.

The patient self-assessed functional outcomes for those shoulders with ≥2 positive cultures for Propionibacterium (the culture-positive group) were compared with shoulders with no positive cultures or only 1 positive culture (the control group).

Below is an example of what is referred to as a 'stealth' presentation in which there were no preoperative symptoms or signs of infection, yet the cultures from revision surgery were strongly positive.

The culture-positive group were 89% male with a mean age of 63.5 ± 7.2 years. The mean Simple Shoulder Test (SST) scores for the 27 culture-positive shoulders improved from 3.2 ± 2.8 points before the surgical procedure to 7.8 ± 3.3 points at a mean follow-up of 45.8 ± 11.7 months after the surgical procedure (p < 0.001), a mean improvement of 49% of the maximum possible improvement. 

The control group were 39% male with a mean age of 67.1 ± 8.1 years. The mean SST scores for the 28 control shoulders improved from 2.6 ± 1.9 points preoperatively to 6.1 ± 3.4 points postoperatively at a mean follow-up of 49.6 ± 11.8 months (p < 0.001), a mean improvement of 37% of the maximum possible improvement. 

Subsequent procedures for persistent pain or stiffness were required in 3 patients (11%) in the culture-positive group and in 3 patients (11%) in the control group; none of the revisions were culture-positive. 

The authors concluded that the clinical outcomes after single-stage revision for Propionibacterium culture-positive shoulders were at least as good as the outcomes in revision procedures for control shoulders. Two-stage revision procedures may not be necessary in the management of these cases. 

Fourteen patients reported side effects to antibiotics, indication that patients should be educated with regard to potential antibiotic side effects.

Comment: While a two-stage revision may be indicated for the 'obvious' infections, this article suggests that a single stage revision may be sufficient for the management of 'stealth' presentations.

This article carefully distinguishes between (a) the 'obvious' presentation of a shoulder infection with findings such as abnormal blood tests (WBC, ESR, C-reactive protein), erythema, fever, and/or wound drainage from (b) the 'stealth' presentation in which none of these findings are present in shoulder arthroplasties revised for pain, stiffness or component loosening combined with cultures positive for organisms such as Propionibacterium. While in the past some have referred to the second group of  cases as "unexpected positive cultures in revision shoulder arthroplasty", it is now preferable simply to report the clinical findings (i.e. is there obvious clinical evidence of infection?), the number of specimens, and the culture results. Furthermore, since it is not currently possible to distinguish "true infections", "contamination", "false-positive cultures", "non-pathogenic Propionibacterium growth", it is preferable to avoid these terms and, again, reporting the clinical findings, the number of specimens, and the culture results.


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