The management of acute PJI presents great challenge to orthopaedic surgeons. To extract the implant and perform a one-stage or two-stage revision may be a hard choice for both the patients and surgeons. Thus DAIR, which retains the protheses, remains the mainstay treatment for acute PJI. However, its efficacy has been debated during the past few decades. Several studies have reported an overall success rate of lower than 50% [11, 12, 14–17, 21–23]. (Table 2)
A systematic review by Silva, which included 30 articles with 530 DAIR for PJI following TKA, revealed the success rate of only 32.6% after a mean 4-year follow-up . A similar research by Romano at 9 years later including 14 article and 710 acute PJI cases found the success rate was still not high, standing at 46% . DAIR was therefore concerned because a failed DAIR would increase the likelihood of failure of the subsequent two-stage revision [32, 33]. From the recent 2018 international concensus meeting (ICM), 96% of delegates agree that the effectiveness of DAIR is still unclear due to lack of comparative data among the treatment options, and limited evidence to suggest superiority of any one treatment. The treatment decision must be made on a case-by-case basis and account for underlying medical conditions, infection history, organism characteristics, and surgical history. DAIR is most appropriate for acute PJI without complicating factors, such as extensive and pervasive infection by a high virulence or resistant organism .
This is a single-surgeon series reporting the outcome of standardized DAIR procedure for acute PJI. The main finding is DAIR has an overall high success rate for acute PJI. Despite the general not high success rate, however, after a deep review of the literature we found great heterogeneity of the included population. In some reports, the polyethylene inserts/femoral heads were not exchanged during DAIR. This may lead to incomplete debridement as the surgeon would have no access to the posterior joint capsule and bilateral gutters. Along with the bioﬁlm adhered to the insert/femoral head, keeping it would definitely increase the bioburden of infection. Also, surgeons would have the chance to clean the tibial/femoral component once the insert or head is removed. Second, in some other reports, surgeries were performed by different surgeons with various experience and surgical skills. DAIR is an urgent surgery which requires a radical debridement of all the infected tissues and a standardized operating procedure should be set up. Finally, for most research reported, the culture positive rate was not high. This may increase the likelihood of failure because no pathogen-specific antibiotics could be used. In our case series, all the DAIR procedures were performed by the single experienced senior surgeon using standardized surgical procedure. The culture positive rate was as high as 90% following a strictly standardized culture protocol, and with the help of mNGS technique, we were able to identify pathogens in over 90% of patients and chose pathogen-specific antibiotics according to the drug-resistant results.
NGS, especially mNGS, is an evolving technology widely applied in clinical diagnosis . mNGS sequences all nucleic acid fragments in a clinical sample, enabling the use of bioinformatics method to obtain microbial sequences and species information and therefore identifies the pathogen. Recently, owing to the substantial cost reduction, mNGS has also been increasingly applied to the diagnosis of bone and joint infection . Our previous reports have shown that mNGS has potential in identifying pathogens even in cases with antibiotic treatment and in cases with rarely-seen pathogens [37, 38]. In this limited cohort of patients, mNGS also identified additional microorganisms in 2 cases, which added another evidence that mNGS may serve as a potential fast tool to diagnose PJI. However, more studies are warranted to prove its true efficacy. In our current practice, mNGS has been used as a routine diagnostic tool for suspected bone and joint infections.
Our second finding was DAIR could be considered even in patients whose symptoms were sustained for over 1 month.In our series, five cases were presented with symptom onset between 4 weeks to 8 weeks. These patients were all managed with DAIR and we saw no infection relapse during a minimum one-year follow up. A similar study was reported by Ottesen et al, which showed a high success rate of 88% in patients within 42 days . Nonetheless, we have no experience in managing cases whose symptoms have been for over 3 months. Ottesen reported 10 such patients with DAIR with success rate of 60%, which was encouraging . However, it merits further evaluation to see if DAIR could be performed to treat delayed or chronic PJI.
The third finding of our study was that we showed DAIR had high success rate for Staphylococcal infections. All the 3 cases with staphylococcus aureus infections were successfully treated, and even for the methicillin-resistant staphylococcus, as was seen in our 9 MRSE infections, DAIR completely eradicated infection. Staphylococcal infection has been viewed as a risk factor for failed DAIR, as literature reported high failure rate ranging from 45% to 76% (Table 3). One possible explanation is that Staphylococcus is more easier to form biofilm on the surface of implants, as well as its drug-resistance to antibiotics . Thus several researchers have proposed staphylococcal infection to be a surgical contradiction to DAIR, especially for methicillin-resistant staphylococcus [39, 40] . For streptococcal infection, our limited data demonstrated a general satisfactory success rate of 71.4%(5/7), which was still higher than the data from a multi-center study (35%, 11/31) .
Another finding of this study is on the antibiotics regime. In our series, IV antibiotics were generally used for 2 weeks followed by 4 weeks of oral antibiotics, regardless of hip or knee infection. The 2013 guideline of Infectious Diseases Society of America (IDSA) has recommended IV antibiotics for 2–6 weeks followed by oral antibiotics for 3 months for hip infections, and 6 months for knee infections for treating acute PJI . Nonetheless, the optimal duration of antibiotics has been controversial. Various studies have shown a similar infection eradication rate between short-term antibiotics and long-term antibiotics regime . And a recent multi-center randomized trails did show that oral antibiotic therapy was noninferior to intravenous antibiotic therapy when used during the first 6 weeks for complex orthopedic infection . Long-term antibiotics regime brings several adverse effects to the patients, and our study suggest a short-term antibiotics (2 weeks IV plus 4 weeks of oral) can be considered for acute PJI. More randomized controlled trials are warranted to address this issue.
There are several limitations of this study that need to be acknowledged. First, same as other reports, this is a retrospective study without comparative controls and with limited sample size. Second, the follow-up period is relatively short, and it’s possible that some slow, low-virulence infections might present itself later than our mean 2-year follow-up period. The long-term treatment outcome remains to be evaluated.