Twenty-five patients (14 in the success group and 11 in the failure group) were on suppressive antibiotic therapy at the time of final follow-up. The infection rate did not differ significantly between the 25 patients who were on chronic suppression (44%) and the 20 who were not (55%) (odds ratio [OR] = 0.64; 95% confidence interval [CI] = 0.2 to 2.09; p = 0.46). When this variable was analyzed in isolation for type-B2 hosts (the most common cohort), the reinfection rate was lower, but not significantly so, for those treated with suppressive antibiotics (38% [3/8] compared with 58% [7/12]; p = 0.83).
Host status was found to be a risk factor for failure (p = 0.084 for type A versus type C). We found a relationship between infection recurrence after the second 2-stage reimplantation and worsening grades for the host and local condition of the extremity (p = 0.06). A revision for reinfection was performed in 30% (3) of the 10 uncompromised hosts (type A), 48% (13) of the 27 medically compromised hosts (type B), and 75% (6) of the 8 very medically ill patients (type C) following the second 2-stage exchange arthroplasty. Resection or transfemoral amputation was performed in 4 of the 8 type-C hosts compared with 1 of the 10 type-A hosts. The infection recurred in both of the patients with the worst host and extremity grades (type C3). The reinfection rate was 50% (10 of 20) in the most common group of patients according to host and extremity grade (type B2) (Table V).
Of the 23 patients who had infection-free implant survival, 13 were immunocompromised (type-B or C) hosts and had a compromised (type-2 or 3) lower extremity. Four type-B hosts (15%) eventually had a resection or transfemoral amputation.
Referral to our hospital from an outside institution was not found to be a significant risk factor for failure (p = 0.69).
Complications occurred in 14 patients (31%). The most common was a new disruption of the extensor mechanism (3 cases), intraoperative fracture at the time of resection or reimplantation (3 knees), postoperative fracture (2 knees), aseptic loosening of the implant (2 knees), stem-condyle bolt failure in a varus-valgus constraining knee implant (3 knees), and instability (2 knees). Only 11 patients (24%) did not have a complication or a reoperation for infection, intraoperative complications, or postoperative sequela.
Reinfection after 2-stage exchange arthroplasty is a difficult clinical scenario with limited data on appropriate treatment algorithms. The results of subsequent reimplantation procedures in this setting remain unknown. We sought to define the results of a second 2-stage exchange arthroplasty for reinfection as well as the risk factors for failure based on host and extremity grades derived with the MSIS staging system.
In our study, the overall reinfection rate after a second 2-stage exchange arthroplasty for periprosthetic knee infection was 49% (22 of 45). Previous literature has shown higher success rates in terms of infection eradication following a second 2-stage exchange procedure6,7. However, the patients in those studies were type-A hosts. For example, Azzam et al.6 reported that 14 of 18 self-stated healthy (type-A) patients had successful eradication of infection after undergoing a second 2-stage reimplantation for the treatment of periprosthetic knee infection. Similarly, Backe et al.7 reported a 100% rate of infection eradication at short-term follow-up of patients who were not immunocompromised at the time of reimplantation. Our study differed from these previous reports in that our sample size was larger and we included patients who were compromised hosts (type B or C) and/or had a compromised extremity (type 2 or 3) when they underwent reimplantation. Only 9% of the patients in our study were classified as an uncompromised host with an uncompromised or a not substantially compromised extremity, and 78% were classified as compromised hosts (type B or C). The 30% failure rate (3 of 10) in our medically healthy patients (type-A hosts) was similar to the rates in the previous reports. The reinfection rate substantially increased with declining host and extremity status, with both patients who were considered a compromised host and to have a compromised extremity (type C3) having a reinfection.
To our knowledge, this is the only study in which the results after a second 2-stage exchange arthroplasty were studied in patients stratified according to host status and condition of the extremity. We showed that host factors and overall wound status play a substantial role in outcomes following a second 2-stage exchange arthroplasty. Many of the patients in this study were classified as a compromised host or as having a compromised extremity, or both, according to the MSIS system as described by McPherson et al.9. Reinfection rates were strongly correlated with worsening host and extremity grades. There was also a strong association between worsening host grade and eventual resection arthroplasty or amputation in this cohort. Of the 8 patients classified as very medically ill (type-C hosts), 4 eventually had a resection or amputation at the time of final follow-up whereas only 1 of the 10 medically healthy (type-A) hosts had such a procedure.
Treatment algorithms have evolved over the years. In a previous study of 24 patients treated for reinfection after a failed 2-stage reimplantation, 2 patients received a subsequent reimplantation, 11 underwent arthrodesis, 6 underwent debridement, 4 were treated with antibiotic suppression, and 1 underwent amputation8. Surgeons have become more likely to attempt a subsequent reimplantation procedure in the setting of reinfection with a goal of improving the functional outcome. The overall complication rate in our study was high (31%), indicating that these procedures are fraught with intraoperative and postoperative problems. Likewise, the revision rate for any reason in our study was 62%.
This study has limitations. Patients selected for a subsequent 2-stage exchange arthroplasty are thought to be the best surgical candidates to undergo this treatment regimen. Those who are deemed too compromised to undergo another 2-stage exchange arthroplasty because of host or limb factors are treated with debridement with component retention, amputation, resection, or arthrodesis. Thus, the patient population that we studied consisted of the best possible candidates for an attempt at infection eradication and another reimplantation. The results of a second 2-stage exchange procedure in a less healthy population, or patients with a more compromised limb, are unknown, and our data cannot be extrapolated to all patients.
Functional scores were not obtained for all patients at the time of follow-up; thus, we could not provide the functional outcomes of the procedure. There was also the potential for bias in this study as the reviewer was not blinded to the outcome while identifying patient characteristics to risk-stratify patients.
Treatment for reinfection following 2-stage exchange arthroplasty for periprosthetic knee infection remains challenging. Our results show that enthusiasm and expectations for infection eradication following a second 2-stage exchange arthroplasty should be tempered for patients with a compromised host and extremity status. Selection of the appropriate treatment for a patient with reinfection following an initial 2-stage exchange arthroplasty involves consideration of host status, extremity status, implant status, bone stock, and microorganism profile. Other reconstructive or salvage options should be considered for the most medically compromised patients rather than making another futile attempt at reimplantation.
Investigation performed at the Mayo Clinic, Rochester, Minnesota
Disclosure: The authors indicated that there was no outside source of funding for this study. The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article.
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