Serum erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) were examined, and arthrocentesis was performed preoperatively if effusion was present. Cultures were taken, both aerobic and anaerobic, and were considered negative if there was no growth at 7 days. Acid fast bacteria cultures and fungal cultures were taken and considered negative if there was no growth after 1 month. Acute infection was defined as one of the following: purulence of the synovial fluid or at the implant site; growth of the same organism from two or more cultures (either synovial fluid or intraoperative tissue). Chronic infection was defined as one of the following: pain at rest, along with ESR and CRP elevation and loosening of the implant; chronic draining sinus; growth of the same organism on two or more cultures [23, 34].
All patients with infection underwent a two-stage revision with removal of the infected joint and placement of an antibiotic-laden, nonarticulating, polymethylmethacrylate spacer. Intraoperative frozen section analysis for acute inflammation was used as a final check before replantation.
Postoperatively, all patients were seen by physical therapy when they reached the hospital floor and assisted to a chair on the same day as surgery. Within 24 hours, patients were seen again by physical therapy and taught to walk and weight bear, as tolerated, to and from the hospital room restroom and down the hallway. After 24 to 48 hours postoperatively, patients were taken to the main physical therapy department where a complete and standard ROM protocol was begun. The in-house physical therapy was supervised and usually took at least 2 hours per patient per day. At discharge, physical therapy was ordered for 2 weeks at home and then for 6 weeks as an outpatient. All patients revised for infection were treated with 6 weeks of parenteral antibiotics with two patients requiring long-term suppression with parenteral followed by oral antibiotics.
The followup routine for patients included clinic visits at 2 weeks, 1 month, 3 months, 6 months, 12 months, and then annual postoperative visits. Clinical examinations and ROM were assessed at each visit. Radiographs were taken and assessed during the immediate postoperative period and also at 2 weeks, 1 month, 3 months, 6 months, 12 months, and annually thereafter. Data were gathered using paper charts, electronic medical records, and relevant imaging modalities. Data were collected on patient demographics and comorbidities, including age, gender, height and weight, active smoking, hypertension, diabetes, history of malignancy, heart disease, and lung disease. Data were collected on operative times, and outcomes after surgery were recorded. From the medical records, data were abstracted on ROM generating a database that showed the changes in ROM throughout the course of recovery. This database included measurements made after the revision until 2 years of followup was obtained. To gather data not available in the medical record, all patients not meeting an end point (74 patients) were asked to come back for a followup appointment. At this appointment, outcome data were collected using the following forms and questionnaires: WOMAC, SF-36 , Knee Society score (KSS) , and Activities of Daily Living (ADLs) . Patients also underwent a physical examination to determine knee ROM and stability and underwent radiographic examination if due for their annual radiographs. These radiographic examinations were used to determine the KSS, for which varus and valgus measurements were needed. These functional assessments were obtained on 45 of the 76 knees (59%) that underwent revision TKAs, 30 of which were performed for aseptic loosening and the remainder being the result of infection. Of the 15 septic knees, six had MRSA identified as the causative organism, whereas the remaining nine had organisms other than MRSA.
Descriptive analysis, including mean, SD and univariate statistics were used to describe the three patient groups we looked at in this study: aseptic revisions, MRSA-negative septic revisions, and MRSA-positive septic revisions. The same approach was used to compare those patients who did and did not return for followup at the specialized research visit. Analysis of variance (ANOVA) was used to compare demographic data among the three treatment groups and between those patients who did and did not have followup at the two year research visit. The Kruskal-Wallis test was used to compare continuous, nonparametric variables, including the WOMAC, SF-36, KSS, and ADLs, and operative times between the three treatment groups. The Mann-Whitney rank-sum test was used to compare the two treatment groups when all infections were grouped together.
We observed no differences between the three treatment groups at final followup for the following indices: WOMAC, ADLs, SF-6, or KSS (Table 3). When all infections were grouped together and compared with the aseptic group, no differences were found.
Intraoperatively, the average operative times were 166 minutes for the MRSA septic group, 149 minutes for the non-MRSA septic group, and 121 minutes for the aseptic group. The MRSA-septic group had operative times that were longer (p = 0.001). Likewise, the non-MRSA-septic group had operative times that were longer (p = 0.012) than the aseptic group. There was no difference between operative times in the MRSA-infected and non-MRSA-infected groups.
Among 10 knees infected with MRSA, no knees had MRSA reinfection after revision. One knee (10%) did become infected with coagulase-negative S. aureus, and this patient underwent an above-knee amputation. Among the 37 non-MRSA septic knees, seven knees had reinfection after revision (18.9%). Irrigation and débridement was used for treatment in five of these knees, and one of these went on to require tibiofemoral arthrodesis. Two of these reinfected knees had superficial infections, and they were managed medically. No amputations were necessary in this group. Of the 56 knees revised for aseptic reasons, two knees had superficial infections (3.6%). Both of these infected knees were managed medically. No irrigation and débridement, amputation, or arthrodesis was used to manage these infections.
Methicillin-resistant S. aureus is a growing problem in health care with deleterious effects on patient mortality and morbidity as well as healthcare economics [1, 5, 12, 25]. The field of orthopaedic surgery has not been spared this problem, and efforts to reduce infection are in use throughout the United States and the world [18, 22]. Total joint reconstruction is no exception. Concerns regarding the decreased retention of the total joint after infection with antibiotic resistant organisms have been studied, with demonstration that such infections can be difficult to manage . In our own experience, these infections can be both difficult to manage and be associated with increased scarring intraoperatively. This led us to ask the question whether these infections might be associated with decreased functional outcome scoring, in addition to presenting difficult infection management issues. We also explored issues related to study limitations as well as reinfection concerns.
We recognize several limitations. First, we included only 43 patients (with 45 of the 103 knees) in our functional assessments. Another 27 patients (27 knees) were ineligible for inclusion because they had met end points, and 31 patients were lost to followup or refused to participate in the study. For many of these patients, a study visit was viewed as an “extra” visit, and many chose not to participate, perhaps as a result of difficulties with driving distances and expense or perhaps as a result of general discontent with their outcomes. Although it is possible patients did not participate as a result of dissatisfaction with their outcomes, we found no indication from the record and 6-month followup that there was a difference between patients with and without final followup. The second major limitation was that we had a low number of patients. A post hoc power analysis for the functional scores revealed that for greater than 80% power to detect differences, assuming an alpha level of 0.05 and an effect size equal to the difference in the outcome measure between the groups, a cohort composed of between 35 (KSS) and 1000 (ADLs) MRSA subjects would be required. Given the lack of power for functional scoring, the risk of accepting the null hypothesis (that there is no difference in functional scores between the MRSA group and other groups) when the null hypothesis is not true (a type II error) is large. Therefore, in terms of functional scoring, this study does not allow definite conclusions to be made.
Barrack et al. reported patients undergoing revision TKA for septic indications had lower Knee Society clinical scores, lower function score, and had more trouble returning to daily activities than patients who had revision for aseptic reasons . We presumed patients with MRSA infections would have diminished functional scores owing to what we qualitatively perceived as an increased scar response to MRSA infections. Contrary to what we presumed, however, we found no differences in functional scores, and a post hoc power analysis revealed that our study was underpowered to detect these differences. Therefore, with the numbers available, we can make no clear conclusions based on the results of this study. In a comparative study to Barrack et al. , Ghanem et al. found patients with knees revised for infections achieved functional, pain, and mental health scores similar to those achieved by patients revised for aseptic reasons . In our study, when all infections were grouped together, we did not observe any difference in outcome score measures. The results of our study were compared to these and other studies (Table 4).
In regard to operative times, we found a longer surgical time for MRSA replantations and non-MRSA replantations than for one-stage revisions for aseptic loosening. While this does demonstrate increased time needed for the operation, we believe this increased time may reflect increased irrigation times, and not necessarily increased time due to hypertrophic scarring.
We found similar rates of reinfection with non-MRSA-infected knees and the MRSA knees. The percentage of recurrence for MRSA-infected knees was lower than, although similar to, that reported in 2007 by Mittal et al. , which included antibiotic-resistant organisms. The reason for these similar rates is unclear. Although non-antibiotic resistant infections may present fewer challenges for eradication, the MRSA infections may have been eradicated at a similar rate due to more aggressive irrigation and débridement, and proper use of antibiotics. However, as stated previously, operative times were not different for MRSA septic and non-MRSA septic knees, perhaps indicating that the aggressiveness of the irrigation and débridement was similar.
The treatment of prosthetic joint sepsis, especially from MRSA, is a difficult, time-consuming, exacting process. This study was underpowered to detect differences in functional outcome scores. However, it did demonstrate numerical score values that add to the existing literature (Table 4). It also suggested that operative times for revisions performed for infections tend to be longer than revisions performed for aseptic indications, although the specific reason for this increased time is still unclear. Furthermore, it suggests that aggressive and appropriate treatment of MRSA septic knees and non-MRSA septic knees may lead to similar rates of infection eradication.
We thank Dr. Brian Klatt and Dr. Lawrence Crossett for their contributions to this project.
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