Re-infection Rates With Antibiotics After Revision THA
Re-infection Rates With Antibiotics After Revision THA
While the risk of infection after primary THA has been reduced to approximately 1% in most cases, there remains a substantial percentage of patients who became reinfected after two-stage reimplantation. These reinfections can be extremely difficult to eradicate, costing in excess of $100,000 per revision. Because of this, it is important to look for simple, cost-effective, and straightforward methods to improve patient outcomes and reduce the rates of reinfection after two-stage revision THA. After the senior author had moved to his current institution, he noticed an increase in infection rates, which prompted further inquiry into the oral antibiotic regimen being prescribed by the various infectious disease consultants. This led to the discovery that some patients had received postoperative oral antibiotics while others had not and prompted the present investigation.
Antibiotic use during two-stage revision arthroplasty has been discussed regarding duration of treatment, specific antimicrobial agents, and their effect on specific organisms (eg, MRSA). The appropriate duration of postoperative parental antibiotics has been a topic of contention. In a study of 31 consecutive infected THAs, McKenna et al. reported no reinfections and concluded a shortened postoperative course of parenteral antibiotics was successful in treating infection. Bassetti et al. reviewed the duration of parenteral versus oral linezolid and found both were effective in orthopaedic procedures. Additionally, Oussedik et al. concluded linezolid is effective for the oral treatment of infected joint arthroplasties. Other authors have noted greater difficulty when treating periprosthetic hip infections when drug-resistant pathogenic organisms, such as MRSA, are identified. In 2008, Pulido et al. reported on 66 drug-resistant periprosthetic infections with either MRSA or MRSE infections with 32 undergoing two-stage revisions. Only 24 of these 32 patients had their infection eradicated (75% success rate). In our study, MRSA infections were the most common infection in both cohorts (those receiving and those not receiving postoperative antibiotics). In contrast to the findings by Pulido et al., the patients who received postoperative oral antibiotics had no reinfections. This suggests oral antibiotics after reimplantation THA may improve reinfection outcomes when treating drug-resistant organisms.
The infection rate in this report after aseptic hip revisions was 0.5% and is consistent with that reported in the literature. Previously reported success rates for two-stage revisions range from 86% to 94%, which are consistent with our findings (Table 4). The cohort that received postoperative oral antibiotics had no reinfections, which is comparable to the low infection rates seen by some authors in primary arthroplasty procedures. In contrast, the cohort that did not receive postoperative oral antibiotics had a higher infection rate than the aseptic revision cohort, with the reinfection rate comparable to the reports in the literature of higher reinfection rates after two-stage revision for infected THAs. It is uncertain what the mechanism is that leads to this difference in re-infection rates. The authors postulate that these oral antibiotics may have prevented biofilm formation on the new implants, or may have provided further bacteriocidal effects the further eliminate any remaining bacterial load. Although our sampling for acute inflammation on frozen pathologic sections has low false negative rates, there is still variability in the quality of pathology departments and their ability to identify retained signs of inflammation.
There were several limitations of this study. This was an observational study and there was no preselected assignment of patients based upon any demographic factors. While we recognize these two groups were not randomized, we believe the two groups had comparable demographic data, primary diagnoses, and distributions of infecting organisms. Next is the concern regarding the power of the study, given the small sample size. A retrospective power analysis determined the study had 91% power and the ability to detect a 7% difference in infection rates. With minimal differences in confounders, there still remains the possibility that the two cohorts may have had a selection bias, which could have skewed the results. We believe that the study was sufficiently powered to make the preliminary conclusion that oral antibiotics after two-stage revision THA may reduce periprosthetic hip reinfection rates in the hopes of encouraging further, more rigorous studies of this nature in the future. Additionally, it is always difficult to determine the exact pathogenesis of the repeat infection: i.e. was the infection due to a recurrence of the original pathogen, or is the infection a new event, independent of previous treatments. Furthermore, prolonged courses of antibiotics may have an improved ability to eradicate remnant pathogens that were not originally detected at the re-implantation procedure. The emergence of drug resistant organisms is always a concern when prescribing antibiotics, even though all patients who are undergoing 2-stage revision arthroplasty have already been treated with a minimum of 6 weeks of IV antibiotics. This was made increasingly difficult based on the number of patients with negative cultures. This may be due to a lack of cultures prior to the initiation of antibiotics; frequently, primary care physicians or emergency department staff will start patients on antimicrobial therapy prior to attaining cultures. In future studies, care should be taken to ensure that cultures are taken prior to the initiation of antibiotic therapy. Additionally, we did not address the effect of duration of antibiotic treatment (i.e. 2 weeks of antibiotic therapy may be comparably effective in reducing re-infection rates as the median 6 weeks reported in the present study). Future prospective, randomized studies could possibly evaluate the efficacy of different durations of therapy; however, the power needed for such a study may be prohibitively small to detect a difference given the positive results reported here with 6 weeks of treatment. Many factors, including the virulence of the infecting organism, antibiotic mechanisms, patient-specific factors (such as immunosuppression), and specific organism-antibiotic susceptibilities can influence the required duration of antibiotics. In future work, many of these factors should be rigorously addressed in the form of a prospective randomized trial to determine the optimal treatment type and time.
Discussion
While the risk of infection after primary THA has been reduced to approximately 1% in most cases, there remains a substantial percentage of patients who became reinfected after two-stage reimplantation. These reinfections can be extremely difficult to eradicate, costing in excess of $100,000 per revision. Because of this, it is important to look for simple, cost-effective, and straightforward methods to improve patient outcomes and reduce the rates of reinfection after two-stage revision THA. After the senior author had moved to his current institution, he noticed an increase in infection rates, which prompted further inquiry into the oral antibiotic regimen being prescribed by the various infectious disease consultants. This led to the discovery that some patients had received postoperative oral antibiotics while others had not and prompted the present investigation.
Antibiotic use during two-stage revision arthroplasty has been discussed regarding duration of treatment, specific antimicrobial agents, and their effect on specific organisms (eg, MRSA). The appropriate duration of postoperative parental antibiotics has been a topic of contention. In a study of 31 consecutive infected THAs, McKenna et al. reported no reinfections and concluded a shortened postoperative course of parenteral antibiotics was successful in treating infection. Bassetti et al. reviewed the duration of parenteral versus oral linezolid and found both were effective in orthopaedic procedures. Additionally, Oussedik et al. concluded linezolid is effective for the oral treatment of infected joint arthroplasties. Other authors have noted greater difficulty when treating periprosthetic hip infections when drug-resistant pathogenic organisms, such as MRSA, are identified. In 2008, Pulido et al. reported on 66 drug-resistant periprosthetic infections with either MRSA or MRSE infections with 32 undergoing two-stage revisions. Only 24 of these 32 patients had their infection eradicated (75% success rate). In our study, MRSA infections were the most common infection in both cohorts (those receiving and those not receiving postoperative antibiotics). In contrast to the findings by Pulido et al., the patients who received postoperative oral antibiotics had no reinfections. This suggests oral antibiotics after reimplantation THA may improve reinfection outcomes when treating drug-resistant organisms.
The infection rate in this report after aseptic hip revisions was 0.5% and is consistent with that reported in the literature. Previously reported success rates for two-stage revisions range from 86% to 94%, which are consistent with our findings (Table 4). The cohort that received postoperative oral antibiotics had no reinfections, which is comparable to the low infection rates seen by some authors in primary arthroplasty procedures. In contrast, the cohort that did not receive postoperative oral antibiotics had a higher infection rate than the aseptic revision cohort, with the reinfection rate comparable to the reports in the literature of higher reinfection rates after two-stage revision for infected THAs. It is uncertain what the mechanism is that leads to this difference in re-infection rates. The authors postulate that these oral antibiotics may have prevented biofilm formation on the new implants, or may have provided further bacteriocidal effects the further eliminate any remaining bacterial load. Although our sampling for acute inflammation on frozen pathologic sections has low false negative rates, there is still variability in the quality of pathology departments and their ability to identify retained signs of inflammation.
There were several limitations of this study. This was an observational study and there was no preselected assignment of patients based upon any demographic factors. While we recognize these two groups were not randomized, we believe the two groups had comparable demographic data, primary diagnoses, and distributions of infecting organisms. Next is the concern regarding the power of the study, given the small sample size. A retrospective power analysis determined the study had 91% power and the ability to detect a 7% difference in infection rates. With minimal differences in confounders, there still remains the possibility that the two cohorts may have had a selection bias, which could have skewed the results. We believe that the study was sufficiently powered to make the preliminary conclusion that oral antibiotics after two-stage revision THA may reduce periprosthetic hip reinfection rates in the hopes of encouraging further, more rigorous studies of this nature in the future. Additionally, it is always difficult to determine the exact pathogenesis of the repeat infection: i.e. was the infection due to a recurrence of the original pathogen, or is the infection a new event, independent of previous treatments. Furthermore, prolonged courses of antibiotics may have an improved ability to eradicate remnant pathogens that were not originally detected at the re-implantation procedure. The emergence of drug resistant organisms is always a concern when prescribing antibiotics, even though all patients who are undergoing 2-stage revision arthroplasty have already been treated with a minimum of 6 weeks of IV antibiotics. This was made increasingly difficult based on the number of patients with negative cultures. This may be due to a lack of cultures prior to the initiation of antibiotics; frequently, primary care physicians or emergency department staff will start patients on antimicrobial therapy prior to attaining cultures. In future studies, care should be taken to ensure that cultures are taken prior to the initiation of antibiotic therapy. Additionally, we did not address the effect of duration of antibiotic treatment (i.e. 2 weeks of antibiotic therapy may be comparably effective in reducing re-infection rates as the median 6 weeks reported in the present study). Future prospective, randomized studies could possibly evaluate the efficacy of different durations of therapy; however, the power needed for such a study may be prohibitively small to detect a difference given the positive results reported here with 6 weeks of treatment. Many factors, including the virulence of the infecting organism, antibiotic mechanisms, patient-specific factors (such as immunosuppression), and specific organism-antibiotic susceptibilities can influence the required duration of antibiotics. In future work, many of these factors should be rigorously addressed in the form of a prospective randomized trial to determine the optimal treatment type and time.
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