Background: Revision shoulder arthroplasties are often culture-positive for Propionibacterium. This study tests 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.
Methods: Fifty-five shoulders without obvious clinical evidence of infection had a single-stage revision arthroplasty. The patient self-assessed functional outcomes for 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).
Results: The culture-positive group had 89% male patients, with a mean age (and standard deviation) 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 had 39% male patients, 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. Fourteen patients reported side effects to antibiotics.
Conclusions: 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. Patients should be educated with regard to potential antibiotic side effects.
Level of Evidence: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.
1Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington
2University of Washington School of Medicine, Seattle, Washington
3South Texas Regional Medical Center, Jourdanton, Texas
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With the increased number of primary and revision shoulder arthroplasties being performed1, the burden of periprosthetic shoulder infections is rising2. The majority of these infections are associated with Propionibacterium3-5. Because of its low virulence, patients with failed shoulder arthroplasties that are culture-positive for Propionibacterium often do not present with obvious signs of infection such as swelling, erythema, and drainage; instead, these patients typically present with the stealth signs of vague pain, stiffness, and component loosening, often long after the index arthroplasty3,6. Intraoperative findings may include cloudy fluid, osteolysis, and a thick periprosthetic membrane but frequently show no obvious evidence of acute infection, such as purulent fluid3. Thus, making a diagnosis of infection at the time of the surgical procedure is often difficult, and the definitive diagnosis must await the result of intraoperative cultures7,8. However, unless definitive surgical and antibiotic treatment is initiated at the time of the surgical procedure, the chances of eliminating an infection are diminished. Thus, at the time of revision of a failed arthroplasty, the surgeon must decide with incomplete information whether to address only the apparent mechanical causes of the failure (stiffness, loosening, instability, cuff failure) or to carry out a revision and antibiotic treatment that would be appropriate for a failed arthroplasty with positive cultures.
Recognizing that >40% of shoulders undergoing revision arthroplasty are likely to be culture-positive3, our approach is to treat each arthroplasty revised for pain, component loosening, or stiffness as if it were culture-positive until proven otherwise; we use a single-stage exchange and immediate antibiotic therapy until the results of the cultures are finalized at 3 weeks after the surgical procedure and continue antibiotic treatment for 6 months if ≥2 of the cultures are positive for Propionibacterium. This study tests the hypothesis that the clinical outcomes of revising failed arthroplasties that have multiple positive cultures for Propionibacterium with a single-stage revision and immediate antibiotic therapy are not inferior to the clinical outcomes of revising failed shoulder arthroplasties that have no positive cultures or only 1 positive culture.
Materials and Methods
This retrospective study (approved by our institutional review board) identified 89 shoulders undergoing a revision arthroplasty by a single surgeon for pain, stiffness, or component loosening but without clinically obvious evidence of infection between November 2009 and May 2013. All 55 cases that had a minimum of 2 years of clinical follow-up were included in our analysis. During this time, 6 additional patients had a failed shoulder arthroplasty associated with gross purulence and sinus-tract formation; these underwent two-stage revisions and were not included in this analysis of single-stage revisions.
Each shoulder was managed as if it was infected. After a standard set of at least 5 specimens including the collar membrane, humeral canal tissue, humeral explant, glenoid explant, and periglenoid tissue was collected for culture, a single-stage revision was performed. In most cases, the failed arthroplasty was converted to a new hemiarthroplasty inserted using allograft that had been soaked in a solution of 1 g of vancomycin powder mixed with 10 mL of saline solution after removal of the extant components, debridement, and lysis of adhesions (Fig. 1). If glenoid-based pain was suspected and glenoid bone stock and quality were adequate for implantation of a glenoid component, a revision to a total shoulder arthroplasty was performed. Those patients with pseudoparalysis or without adequate rotator cuff function were converted to a reverse arthroplasty. As preoperative tests have proven ineffective in identifying the presence or absence of Propionibacterium in the shoulder, preoperative serum laboratory values did not influence treatment.
Preoperative antibiotics were withheld until culture specimens were taken; a minimum of 5 specimens were obtained from each shoulder, including synovial and capsular tissue; the membrane between the prosthetic head and stem; tissue from the humeral canal; the humeral explant; the glenoid explant; and tissue surrounding the glenoid. Each specimen was harvested using a sterile rongeur or a sterile knife blade with sterile forceps. Each instrument used was individually peel-packed and opened just prior to specimen sampling; any instrument touching the skin or subcutaneous tissue was not used for specimen handling. The method of culturing samples has previously been described7. Specimens were processed by the laboratory within 1 hour after the surgical procedure in a Class-2 laminar flow biological safety cabinet. Fluid and homogenized tissue specimens were inoculated onto the following microbiological media: blood agar (trypticase soy agar with 5% sheep blood), chocolate agar, Brucella agar (with blood, hemin, and vitamin K), and brain-heart infusion broth. All media, with the exception of the Brucella agar, were incubated at 37°C with 5% carbon dioxide for 21 days. Brucella agar plates were incubated anaerobically at 37°C for 21 days. Plates were sealed in a manner that allowed sterile aeration without desiccation. Media were examined daily for growth visually but were only opened if growth was noted. Bacteria that were isolated received a full species-level identification by means of 16S rDNA sequencing, as described previously8. Shoulders were defined as culture-positive for Propionibacterium if ≥2 specimens were positive on culture for this organism9. Shoulders with 1 positive culture or 0 positive cultures were defined as controls.
After all culture specimens were obtained, 15 mg/kg of vancomycin and 2 g of ceftriaxone were administered intravenously as prophylaxis unless there was a documented allergy, in which case clindamycin was used. The patients were placed onto one of two initial postoperative antibiotic protocols based on the surgeon’s index of suspicion for infection and considering the observations published by Pottinger et al.3. The postoperative antibiotic regimen was determined in consultation with our infectious disease service. In cases in which there was a high index of suspicion, the patient was maintained on intravenous ceftriaxone through a peripherally inserted central catheter (PICC); intravenous vancomycin was discontinued unless cultures were positive for mecA coagulase-negative Staphylococcus. If the cultures were negative at 3 weeks, all antibiotics were discontinued. In cases in which there was a low index of suspicion for infection, patients were placed on oral amoxicillin and clavulanate either until the cultures were negative at 21 days or until 2 cultures with the same bacterial species became positive. With either initial postoperative protocol, if ≥2 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 6 months.
Data and Statistical Analysis
The medical records were reviewed to identify patient demographic characteristics, operative findings, operative procedure, culture results, antibiotic treatment, preoperative and postoperative Simple Shoulder Test (SST) scores, and Single Assessment Numeric Evaluation (SANE) and visual analog scale (VAS) pain scores. Means and standard deviations were calculated for continuous variables, and frequencies were tabulated for categorical variables. Patients with ≥2 positive Propionibacterium cultures (the culture-positive group) were compared with patients with 1 positive culture or 0 positive cultures for Propionibacterium (the control group). Significance testing was performed using an unpaired two-tailed t test for continuous variables and Fisher exact and chi-square tests for categorical variables. Significance was set at p < 0.05.
Fifty-five shoulders that underwent revision shoulder arthroplasties had a minimum of 2 years of clinical follow-up (mean, 47.8 ± 11.8 months). Patient and procedure characteristics are summarized in Table I. The culture-positive group had a higher proportion of male patients (89%) compared with the control group (39%) (p < 0.001).
Twenty-seven shoulders had ≥2 positive cultures for Propionibacterium; the patients had a mean age of 63.5 ± 7.2 years. At a mean follow-up of 45.8 ± 11.7 months, their mean SST scores improved from 3.2 ± 2.8 points to 7.8 ± 3.3 points (p < 0.001) representing a mean improvement of 49% of the maximal possible improvement (Table II). Nineteen (70%) of the 27 patients had an improvement in SST scores by more than the minimal clinically important difference of 310. Twenty-eight shoulders were in the control group; the mean patient age was 67.1 ± 8.1 years. At a mean follow-up of 49.6 ± 11.8 months, their mean SST scores improved from 2.6 ± 1.9 points to 6.1 ± 3.4 points (p < 0.001) representing a mean improvement of 37% of the maximal possible improvement. Nineteen (68%) of the 28 patients had an improvement in SST scores by more than the minimal clinically important difference of 3.
In the culture-positive group, subsequent procedures for persistent pain or stiffness were required in 3 patients (11%): 1 who underwent manipulation and 2 who underwent open procedures. None of the culture-positive shoulders had positive cultures at the time of the second revision. In the control group, subsequent procedures for persistent pain or stiffness were required in 3 patients (11%): 1 who underwent manipulation and 2 who underwent open procedures. One of the control shoulders had a single positive culture of Propionibacterium from a total of 8 specimens taken at the time of the second revision.
Of the 33 patients who were asked about adverse effects of antibiotic administration, 14 patients (42%) reported side effects. Eighteen of the 33 patients had received intravenous antibiotics; 7 of these patients experienced gastrointestinal complications, 1 experienced a dermatologic complication, and 1 experienced leukopenia. Fifteen of the 33 patients had received only oral antibiotics; 2 experienced gastrointestinal complications and 3 experienced dermatologic complications.
A high percentage of shoulders that undergo surgical revision arthroplasty have a stealth periprosthetic infection from Propionibacterium that does not present in the same manner as the obvious periprosthetic infections of the knee and hip3. Ideally, surgical and antibiotic treatment of a periprosthetic infection would be initiated at the time of the revision surgical procedure. However, because the results of intraoperative cultures are not finalized until weeks after the procedure, the surgeon is left to choose the surgical and immediate antibiotic treatment without this information. In a series of arthroplasty revisions without obvious clinical evidence of infection, treatment with a single-stage prosthesis exchange and immediate postoperative antibiotics resulted in similar patient-reported outcomes and revision rates in culture-positive shoulders compared with control shoulders.
Of the 27 shoulders that underwent arthroplasties and had positive cultures, none had a recognized recurrence of infection. However, because Propionibacterium can present years after a surgical procedure6 and because patients may have incomplete restoration of comfort and function after revision arthroplasty, we cannot state with confidence that the Propionibacterium was completely eradicated.
Although surgeons often use a two-stage prosthesis exchange to treat obvious periprosthetic shoulder infections11-13, this approach carries an increased risk of morbidity that may not be justified in revision arthroplasties, where a stealth infection is possible but unproven. A single-stage exchange11,14-17 with implant removal, a thorough debridement, and aggressive postoperative antibiotic therapy attempt to optimize the chances of clinical improvement without the morbidity and increased costs of a two-stage procedure.
Aggressive antibiotic therapy is costly and can be associated with medical complications. Although intravenous administration of antibiotics may be the surest way of eradicating any remaining infection after debridement and prosthesis exchange, evidence regarding superiority of intravenous antibiotics over oral antibiotics is not yet clear in the literature18. Further study into the relative efficacy of intravenous antibiotics compared with oral antibiotics would be of value.
The results of this study need to be interpreted in light of certain limitations. First, this was a retrospective case series without comparison with other treatment approaches. Second, we defined a culture-positive shoulder as one having ≥2 specimens that grew Propionibacterium on culture, without incorporating time to positivity into our definition; other definitions could have been used. Third, although the results of our treatment of culture-positive shoulders were at least as good as those of treatment of control shoulders, there are many other factors that could have influenced the outcome of revision arthroplasty; we note, for example, that the culture-positive group had a higher percentage of male patients than the control group. Fourth, this study included only patients with possible stealth-type periprosthetic shoulder infection; the role of single-stage revision in patients with obvious signs of infection was not addressed by this study. Fifth, although the mean follow-up duration in this series was 4 years, we cannot exclude the possibility of delayed reappearance of infection with longer follow-up. Sixth, our protocol treated each shoulder undergoing arthroplasty revision as if it was culture-positive for Propionibacterium until the culture results were known. Although this approach avoided the risk of non-treatment of an infection during the time while culture results were pending, it did subject some control patients to the risks of antibiotic treatment.
In conclusion, at a mean of 4 years after the revision surgical procedure, clinical outcomes after single-stage revision shoulder arthroplasty for pain, stiffness, or component loosening associated with ≥2 positive Propionibacterium cultures are not inferior to outcomes after revision procedures for control shoulders. Two-stage revision procedures may not be necessary in the treatment of these cases.
Investigation performed at the University of Washington, Seattle, Washington
A commentary by Philipp Moroder, MD, et al., is linked to the online version of this article at jbjs.org.
Disclosure: There was no external funding for this investigation. On the Disclosure of Potential Conflicts of Interest forms, which are provided with the online version of the article, one or more of the authors checked “yes” to indicate that the author had a relevant financial relationship in the biomedical arena outside the submitted work.
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