Total hip arthroplasty is one of the most successful surgical interventions in recent decades. With the technological advancement and their incorporation in medicine, potential complications from the procedure, such as early aseptic loosening, instability, joint dislocation, or component malpositioning, are increasingly rare. Periprosthetic joint infection (PJI), however, remains a problem for which a solution has yet to be found. This pathology not only compromises the success of treatment for advanced osteoarthritis but often worsens the overall patient condition, compared to the preoperative status.^[1] The incidence of periprosthetic infections in Bulgaria following primary hip replacement is estimated to be 1.5%–2%.^[2] According to relevant publications on the matter, infection is the third most common cause of revision hip replacement (14.7%) and the most common cause of knee revision surgery (25.2%).^[3-5] According to leading European centers, PJI after hip arthroplasty occurs in 0.5%–1.5% of cases.^[6] According to a publication by Phillips et al., infection is the most catastrophic complication in primary joint replacement.^[7] This finding is confirmed by a 2018 meta-analysis of 20,719 knee arthroplasty patients, treated via a two-stage revision protocol for PJI. The study shows that the mortality rate in the first year was 4.33%, rising to 21.64% by the fifth year.^[8] The costs incurred by healthcare systems for treating this pathology are also enormous. According to the Australian registry, annual costs for treating PJI almost doubled between 2005 and 2010, reaching 566 million dollars in the latter year.^[4] All of this underscores the social significance of the problem and the necessity of finding a solution.

Successful treatment of PJI is directly related to accurate microbiological diagnosis. Proper microbiological diagnosis and identification of antimicrobial susceptibility and resistance of isolated pathogens are crucial for the correct management of this condition. Optimization of antibiotic therapy is linked to reducing the likelihood of developing resistant microorganism strains—yet another healthcare issue, the importance of which is only likely to increase in upcoming years.

The gold standard for PJI treatment remains the two-stage revision protocol. The first stage consists of the removal of the primary arthroplasty components in conjunction with thorough soft-tissue and bony debridement and the implantation of an antibiotic-coated articulating spacer. The second stage is characterized by subsequent revision arthroplasty and is carried out once clinical and laboratory results show eradication of the pathogen. The aim of the one-stage protocol is to reduce the potential risks of higher morbidity and mortality associated with the two-stage surgical protocol. The one-stage protocol also strives to decrease the likelihood of complications during hospitalization (e.g., reduce blood loss, decrease the need for blood transfusion) and improve financial efficiency.^[9-12]

The objective of the present study is to profile the microbiological pathogens in the patient cohort under investigation and to emphasize the significance of the data for the successful treatment of periprosthetic joint infections with one-stage revision.

The definition of periprosthetic joint infection was derived from the 2013 International Consensus Meeting (ICM) on Orthopedic Infections criteria. After 2018 we adopted the ICM Philadelphia criteria (Table 1).^[13,14] The incorporated criteria in this study are divided into two main groups: primary and secondary. The primary criteria are: 1) two positive periprosthetic cultures obtained intraoperatively or via joint aspiration, and/or 2) a superficial sinus tract communicating with the joint cavity.

The diagnosis of PJI is established if any primary criterion is present. If no primary criteria are identified, secondary criteria are evaluated, and PJI is confirmed when at least three of the five secondary criteria are met. The presence of one primary criterion indicates the presence of a PJI. In the absence of these criteria, the diagnostic algorithm includes secondary criteria (see table below).

The study included 33 patients (15 men and 18 women), who underwent one-stage revision between October 2017 and July 2023. The average patient age was 66.7 years. Informed consent from the patients was obtained prior to their inclusion in the study. Approval for the study was obtained from the local ethics committee of the healthcare facility. Medical records for all patients were reviewed and compiled into a standardized database. All patients underwent preoperative diagnostic aspiration of the affected joint. A microbiological pathogen was identified in 31 patients. In two cases, preoperative aspiration yielded no results. Microbiological cultures were also obtained from periprosthetic tissues, which showed macroscopic signs of infection. During surgery, a total of five samples for microbiological investigation were collected from each patient. An isolated microorganism was considered as pathogenic if it was isolated in two or more of the five cultures. Preoperative CRP levels were elevated (>0.6 mg/dL) in 14 patients. ESR was elevated in 17 patients (>40 mm/H). Joint aspiration markers including neutrophil count >2000/mL, differential neutrophil count >70%, and leukocyte esterase (++) were analyzed in 17 patients, showing elevated values in 8 cases. Statistical analysis of the data was performed using SPSS 20.0, with a significance level set at p<0.05.

Patients without septic status, with adequate reparative potential, minimal bone and soft-tissue defects, and no fistula communicating with the joint underwent one-stage revision when the causative pathogen was identified and susceptible to effective bactericidal therapy; infections caused by atypical pathogens or fungi were excluded. A summary of the inclusion and exclusion criteria of the study is presented in Table 2.

Staphylococcus epidermidis was the most frequent cause of PJI, identified in 44.1% of cases. Staphylococcus aureus was found in 5 cases, accounting for 14.7% of the cases (a detailed percentage breakdown by isolated pathogen is presented in Fig. 1). No pathogen was isolated in two patients. No polymicrobial infection was identified in the patient cohort. A detailed breakdown of the isolated pathogens in the patient cohort is presented in Table 3. Antibiotic therapy continued intravenously for 14 days during the period of hospitalization. Upon discharge, each patient was prescribed oral antibiotic treatment for a duration of 4-8 weeks.

The application of the one-stage protocol took into account the preoperative overall status of the patient. Posterior approach to the hip was utilized in all cases. Global hip arthroplasty revision was carried out, using non-cemented revision components.

During an average follow-up of 33 months (range 2-66 months), no recurrence of infection was observed. The average Harris Hip Score (HHS) increased from 54.3 points preoperatively to 72.3 points postoperatively. No neurological injuries or loosening of the arthroplasty components were observed during the follow-up period. Two dislocations were observed at 2 and 4 months, respectively, treated with closed reduction, with no recurrence observed in subsequent follow-up. One lethal outcome was recorded, involving a patient who died from a pulmonary embolism two months postoperatively. Although no infection recurrence was observed during follow-up, the limited sample size and absence of a comparator group preclude definitive conclusions regarding eradication rates.

After the first study of the etiological structure of PJI in Bulgaria from 2019, we now focus on the importance of pathogen isolation for optimal treatment outcomes.^[15] The isolation of a microbiological pathogen is crucial for the success of this procedure. Gram-positive organisms predominated in this cohort, consistent with previously published series. Our data correlates with the relevant publications. In a systematic review from 2021, including 1,236 patients, Balato et al. state that methicillin-sensitive Staphylococcus aureus was isolated in up to 37% of cases.^[16] In another series by Wolff et al., which included younger patients up to 45 years old, Staphylococcus epidermidis was the most commonly isolated pathogen, found in 30.8% of cases.^[17] In our series, methicillin-sensitive Staphylococcus epidermidis was not detected. These differences could be attributed to the genetic diversity of Staphylococcus epidermidis and the specific characteristics of regional antimicrobial resistance, as well as the rise of highly resistant pathogens in recent years. The indications for the one-stage protocol were adhered to since vancomycin (a bacteriostatic antibiotic) was listed in the antibiogram for MRSE. Over a seven-year period, T. Rosteius et al. reported a progressive increase in MRSE, extended-spectrum beta-lactamase (ESBL) bacteria, ampicillin-resistant Enterococcus, Acinetobacter spp., and vancomycin-resistant Enterococcus (VRE). The authors noted a significantly higher frequency of MRSE in revision arthroplasty cases. The only trend showing a decrease was in the frequency of methicillin-resistant Staphylococcus aureus (MRSA), attributed to specific characteristics of this pathogen and adherence to MRSA carriage prevention guidelines through preoperative decolonization.^[18] In our experience, the availability of an effective bactericidal antibiotic was associated with successful outcomes following one-stage revision; however, these observations should be interpreted cautiously given the small cohort size. In a 2020 study by Ohlmeier et al., infection control was attained in 93.1% of cases involving 29 patients with MRSA-caused periprosthetic infections treated with a one-stage protocol. These results are comparable to those of the two-stage protocol.^[19]

Prolongation of antibiotic therapy, based on the antibiogram results, is crucial for the success of the intervention. One-stage treatment of PJI is indicated when a bactericidal, pathogen-sensitive antibiotic regimen is available, including biofilm-active agents such as rifampicin when required (e.g., for Staphylococcus spp. or Cutibacterium spp.). Difficult-to-treat pathogens, which lack sensitivity to biofilm-active antibiotics, can only be suppressed by extending systemic antibiotic therapy. In these cases, prolonged suppressive therapy may be a valid option.^[20] Gram-negative bacteria should be treated with fluoroquinolones during the post-hospitalization period and the use of rifampicin should be avoided.^[21]

Cessation of antibiotic therapy two weeks prior to joint aspiration is crucial for isolating the pathogen. According to Parvizi et al., this approach increases the likelihood of correct diagnosis and appropriate therapy. Contrarily, а recent study advises starting antibiotic therapy as soon as an infection is suspected. According to the authors, systemic antibiotic administration does not affect cultures and delaying therapy decreases the chances of successful treatment.^[22] In our cohort, six patients had infections caused by gram-negative bacteria. Implementing a one-stage protocol in this setting is a challenging task. No infection-related complications were observed in the small subgroup of patients with Gram-negative infections; however, the limited number of cases does not allow robust conclusions regarding efficacy in this setting. Our results correlate with the findings of Yicheng et al., who recommend intra-articular infusion of carbapenems when diagnosing a gram-negative organism, in combination with systemic antibiotics based on the antibiogram. The goal is to increase local concentration while avoiding systemic side effects.^[23] Concurrent use of fluoroquinolones in these cases is highly recommended. This treatment regimen provides two key benefits. It achieves good tissue penetration in bone and joint structures and exhibits anti-biofilm activity against Gram-negative bacteria.^[24]

Citak et al. identified risk factors for the failure of one-stage revision. According to their study, the isolation of Enterococcus and Streptococcus spp. significantly reduces the likelihood of a successful intervention.^[25] Similar results are observed with the two-stage protocol.^[26,27] In our series, we observed six patients with infections caused by these pathogens. No recurrence of infection was noted after eight weeks of antibiotic therapy in our cohort.

When comparing our results with contemporary two-stage revision series and registry-level analyses, several important points emerge. Recent systematic reviews and meta-analyses of one-stage versus two-stage revision report no consistent, clinically important difference in reinfection or reoperation rates when patients are selected appropriately, although study heterogeneity remains high.^[28] Large series and pooled analyses of two-stage exchange report infection eradication rates commonly in the ~74%–88% range, depending on joint type, follow-up duration, and whether repeat or complex cases are included.^[29,30] Registry-linked analyses and national registry studies have likewise documented meaningful rates of re-revision and mortality after two-stage exchange, and emphasize substantial interstudy variability driven by case mix and reporting differences.^[31]

Contemporary two-stage revision cohorts and registry studies most commonly report coagulase-negative staphylococci and Staphylococcus aureus as the predominant pathogens, with lower eradication rates observed in the presence of resistant organisms (MRSE/MRSA, vancomycin-resistant enterococci, extended-spectrum β-lactamase–producing bacteria) or multidrug-resistant gram-negative infections. Consequently, two-stage revision is often preferred for polymicrobial, fungal, or difficult-to-treat infections. In our cohort, the predominance of Staphylococcus epidermidis and the availability of targeted antimicrobial therapy are consistent with pathogen profiles in which one-stage exchange has most frequently been reported as feasible. Differences in microbiological distribution across regions and increasing antimicrobial resistance should be considered when interpreting outcomes.^[30,32]

One-stage revision may also be performed in culture-negative infections when indications are broadened or when an unexpected infection is identified during revision for presumed aseptic loosening. In our series, we performed two such procedures. Despite our good results, the difficulty in determining the correct antibiotic therapy required treatment with vancomycin and meropenem during hospitalization and extended oral therapy with rifampicin for three months, combined with levofloxacin for one month after hospital discharge. Despite favorable outcomes in two culture-negative cases, the small number and intensified antibiotic regimens preclude recommending routine extension of one-stage indications in this context. Supportive of this approach is a publication by Zanna et al., who found a failure rate of one-stage revision in undiagnosed PJI at only 9.1% of those followed. According to the author, the lack of a preoperatively isolated pathogen should not be a contraindication for the procedure.^[33]

A key contributor to outcome variability across studies is patient selection. Two-stage protocols are often reserved for polymicrobial or difficult-to-treat organisms, severe soft-tissue compromise, major bone loss, or unstable host physiology. Conversely, many one-stage cohorts (including ours) select hemodynamically stable patients with an identified pathogen and a favorable antibiogram—criteria that enrich for better outcomes. These selection differences lead to confounding by indication and make direct comparisons challenging unless case mix is carefully matched or adjusted. Recent reviews emphasize that selection criteria—not only surgical technique—explain much of the observed outcome variability between one- and two-stage approaches.^[28]

Direct comparison between revision strategies is further limited by heterogeneity in outcome definitions across studies. Recent studies variably report reinfection, reoperation for any cause, implant retention, or composite endpoints such as DOOR-PJI, with substantial differences in follow-up duration. Registry analyses commonly use re-revision as the primary endpoint, whereas clinical series often report infection-free survival, leading to meaningful variation in reported success rates. In the present study, outcomes were defined as the absence of clinical or microbiological recurrence and improvement in Harris Hip Score over a mean follow-up of 33 months; nevertheless, broader adoption of standardized outcome frameworks would improve comparability across studies.^[31,34]

The study’s retrospective design, small sample size, single-center setting, and lack of a control group limit statistical power and generalizability. Selection criteria for one-stage revision may have biased the cohort toward healthier patients and lower-complexity infections, restricting generalizability. Functional outcomes were evaluated using the Harris Hip Score, without the inclusion of quality-of-life assessments or patient-reported outcome measures. As such, the results should be viewed as hypothesis-generating rather than confirmatory. Considering the obtained outcomes with the implementation of the one-stage protocol, we believe that the presented epidemiological profile can be useful in guiding clinical decision-making for tackling the complex and important issue that is periprosthetic joint infection. Regional antimicrobial resistance patterns may limit extrapolation to other healthcare settings.

In this single-center cohort, one-stage revision for periprosthetic hip infection was associated with satisfactory clinical and functional outcomes when patients were carefully selected and treatment was guided by detailed microbiological diagnostics. While these findings are encouraging, larger comparative studies are required to determine the broader applicability and long-term effectiveness of this approach.