Saturday, October 21, 2017

Revision for infection - one stage or two stage?

Two-stage reimplantation for the treatment of deep infection after shoulder arthroplasty

These authors reviewed 50 shoulders having a two stage revision of a periprosthetic shoulder joint infection between 1980 and 2010:  10 hemiarthroplasties, 24 anatomic total shoulder arthroplasties, and 1 reverse total shoulder arthroplasty.

Persistent infection, defined as positive cultures in samples obtained at the time of reimplantation, was identified in 5 shoulders (15%); 50% of persistent infections grew Propionibacterium acnes. Reoperation for "aseptic" glenoid loosening was performed in 2 additional shoulders. 
There was an overall rate of unsatisfactory results approaching 40%. 

Comment: The management of a failed shoulder arthroplasty with a possible infection requires careful thought on how the shoulder is evaluated and how it is managed before the results of cultures taken at surgery are finalized. The approach in the article referenced above should be contrasted to that used in the article posted here:

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

These authors point out that cultures taken at the time 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.

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. As pointed out below, rather than referring to a culture result as 'positive' or 'negative' it is preferable to report the load of the organism in the specimens

Characterizing the Propionibacterium Load in Revision Shoulder Arthroplasty
A Study of 137 Culture-Positive Cases

There has been a tendency in the recent literature to report cultures obtained at revision shoulder arthroplasty as being 'positive' or 'negative' or to assign revised shoulders to arbitrarily defined categories, in some cases distinguished by a single culture result (see below).

These authors took a different approach, one that considered the semi-quantitative results of all the cultures obtained from a revised shoulder - the 'load' of bacteria recovered from the shoulder using a defined culturing protocol.

They studied 137 revision shoulder arthroplasties from which a minimum of 4 specimens had been submitted for culture and that had at least 1 was positive for Propionibacterium. Standard microbiology procedures were used to assign a semiquantitative value (0.1, 1, 2, 3, or 4), called the Specimen Propi Value, to the amount of growth in each specimen. The sum of the Specimen Propi Values for each shoulder was defined as the Shoulder Propi Score, which was then divided by the total number of specimens to calculate the Average Shoulder Propi Score.

They found that the number and percentage of positive specimen-specific cultures (of material obtained from the stem explant, head explant, glenoid explant, humeral membrane, collar membrane, other soft tissue, fluid, or other) per shoulder ranged from 1 to 6 and 14% to 100%. A high percentage of specimens (mean, 43%; median, 50%) from the culture-positive shoulders showed no growth. These observations indicate that Propionibacterium are not evenly distributed through the tissues and implants of a failed shoulder arthroplasty so that more than a few samples are necessary to detect the presence of bacteria.

Another interesting finding was that the type of specimen submitted for culture affected the likelihood of culture positivity. Only 32.6% of the fluid cultures were positive in comparison with 66.5% of the soft-tissue cultures and 55.6% of the cultures of explant specimens. The average Specimen Propi Value (and standard deviation) for fluid specimens (0.35 ± 0.89) was significantly lower than those for the soft-tissue (0.92 ± 1.50) and explant (0.66 ± 0.90) specimens (p < 0.001). This finding provides a possible explanation for the limited utility of a culture-negative joint fluid aspiration in ruling out an infection.

A third intestine finding was the inter-sex difference in Propionibacterium load recovered from revised shoulders. The Shoulder Propi Score was significantly higher in men (3.56 ± 3.74) than in women (1.22 ± 3.11) (p < 0.001). Similarly, men had a significantly higher Average Shoulder Propi Score (0.53 ± 0.51) than women (0.19 ± 0.43) (p < 0.001).

Finally. the authors found that the percent of cultures positive for Propionibacterium varied widely among the cases with no apparent 'threshold' that could be used to distinguish 'definite infection' from 'probable infection' or 'probable contaminant' (see below).

This study provides an approach for standardizing:
(1) the harvesting of specimens = five samples of explants or tissue
(2) the culturing of specimens = aerobic and anaerobic media
(3) the period of observation = at least 17 days
(4) the reporting of culture results = Specimen Propi Value, Shoulder Propi Score and Average Shoulder Propi Score.

Such standardization and objective presentation of the results may facilitate comparison among investigators with respect to the characteristics of revised shoulder arthroplasties and the effectiveness of different surgical and medical approaches to their management.

An informed commentary on this article can be found at "The Emperor May Truly Have New Clothes" J Bone Joint Surg Am, 2017 Jan 18; 99 (2): e7 .

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