Participants and randomization
This prospective, randomized, controlled study was registered in the public Clinical Trial Registry (ChiCTR-INR-17014162) and approval was obtained from the Clinical Trials and Biomedical Ethics Committee of our institution (S2017-085-02). The present study adhered to CONSORT guidelines. All participants were enrolled after written informed consent was obtained before randomization.
Patients with chronic PJI of the hips and scheduled for two-stage exchange arthroplasty were included. PJI diagnosis was made using the Musculoskeletal Infection Society (MSIS) criteria. Patients were excluded from the study if they had a previous allergic history to the listed antibiotics (vancomycin, meropenem, ceftriaxone, linezolid, or bone cement), preoperative hepatic or renal dysfunction, a malignant tumor, ongoing immunosuppressive agents, refusal to participate this study or participation in another clinical study. From January 2018 and November 2018, 35 patients with chronic PJI following primary THA were eligible for study enrollment. Three patients were excluded because of ineligibility. The remaining 32 patients were randomly assigned by means of a computer-generated randomization method to either the study group (non-CSD group, 16 patients) or the control group (CSD group, 16 patients) (Figure 1). The study population included 22 women and 10 men, with a mean age of 60.7 ± 12.3 years (range, 25.0 to 81.0 years). The surgeons and participants who evaluated the concentration and bioassays of the antibiotics were all blinded to group assignment.
An institutional standard protocol of two-stage exchange arthroplasty was performed in all patients. Patients had their implanted components removed followed by thorough and radical debridement of the unvital bone and soft tissue. A minimum of three sets of cultures were obtained. After irrigation, a cement spacer loaded with two combined antibiotics was then implanted. All bone cement spacers were made intra-operatively by hand-mixing 4 g of vancomycin powder (VIANEX S.A., Athens, Greece) and 2 g of meropenem powder (Sumitomo Dainippon Pharma Co. Ltd, Osaka, Japan) per 40 g of methyl-methacrylate cement polymer (Heraeus Medical GmbH, Wehrheim/Ts., Germany). Then, liquid monomer was added and mixed for polymerization. The weight of the implanted cement spacer was recorded intra-operatively. A disposable, closed-suction drainage system (BDA-YS 400 ml; Branden, Shandong, China) was placed in all patients for at least five days. The drains were inserted under the fascia and connected to an evacuator via connector tube. A CSD was placed in all patients after the first-stage surgery to collect drainage for detection of antibiotic concentration. For the study group, the drainage tube remained clamped postoperatively during the study period, which was considered non-use of a CSD. For the control group, the drainage tube was clamped for only 2 hours postoperatively and then remained open until removal of the drain. All patients received ceftriaxone (2 g IV) at the induction of anesthesia preoperatively. Intravenous (IV) linezolid (0.6 g IV q 12 hour) and ceftriaxone (2 g IV q 24 hour) were used in the first five days following spacer implantation. After the study period (5 days following spacer implantation), the antibiotic regimen was decided based on the intraoperative culture sensitivity reports and institutional guidelines.
After implantation of the cement spacer, 5-mL fresh aliquots of drainage were collected under sterile conditions every 24 hours for the first five days, and the drainage container was changed at the time of drainage collection. After the given study period, the drain was removed if the daily drainage amount was less than 50 mL. Additionally, 10 mL of peripheral venous blood was collected during the first 24 hours following implantation of the spacer. All samples were stored and frozen at -80°C for no more than three months. The reimplantation was performed after 2-4 weeks of antibiotic holiday and the soft tissue was free of local heat, erythema, swelling, and any infection-related symptoms.
Determination of antibiotic concentrations
The concentrations of vancomycin and meropenem in the drainage were measured daily for 5 days by using high-performance liquid chromatography (HPLC) assay carried out on an Agilent 1260 Infinity chromatograph with a Thermo Hypersil C18 column (150 mm by 4.6 mm; 5 μm particle size). The standard calibration curve consisted of eleven different standard concentrations (0.625, 1.25, 2.5, 5, 10, 20, 40, 80, 160, 320, 640 and 1280 μg/mL). The mobile phase consisted of acetonitrile-10.53 mm ammonium acetate (composite ratio, 95/5, pH 4) for meropenem and monopotassium phosphate (25 mmol/L)-methanol (86/14, pH 2.4) for vancomycin. The flow-rate was 1.0 mL/min, and the detection wavelengths were 298 nm and 236 nm for meropenem and vancomycin, respectively. The injection volume was 20 μL, and the temperature of the column was 30°C. The HPLC system had sensitivities of 0.5 μg/mL for vancomycin and 0.6 μg/mL for meropenem. The concentrations of antibiotics in the drainage samples were determined by comparison with the peak areas of standard curves prepared daily.
Bioassay of Antibiotic Activity
The bioactivity of the drainage and peripheral venous blood were assessed using an agar disk diffusion bioassay, conducted as described by Hsu et al. Discs containing 35 μL of joint fluid were placed on agar seeded with methicillin-sensitive Staphylococcus aureus (MSSA) (ATCC 25923), methicillin-resistant Staphylococcus aureus (MRSA) (ATCC 43300), and E. coli (ATCC 25922). Inhibitory activity of the disks was determined after 24-hour incubation at 37°C. The diameters of the inhibition zones were measured using a caliper. All samples were tested three times.
Sample size calculation
A noninferiority test was conducted to determine the sample size. Prior study data have indicated 100% antibacterial activity of joint drainage in patients with a CSD in the first week following spacer implantation,[2, 12, 13] so we planned for a minimum expected antibacterial activity rate of 95%. We used a difference (delta value) of 20%, a power of 80%, and an alpha error of 0.05; a sample size of at least 14 for each group was determined. Totally, the present study included 32 patients with 160 drainage samples.
Categorical variables were presented as frequencies and percentages and continuous variables as the means and standard deviation (M±SD). The clinical characteristics between groups were compared with the use of the independent t-test or Mann-Whitney test for continuous variables and the chi-square test for categorical variables. Patients in the control group were further divided into two subgroups based on the median of total drainage volume (400 mL). Univariate linear regression analysis was used to examine the association between drainage volume (as both continuous and categorical variables) and antibiotic concentrations in the joint fluid. β-coefficient and 95% confidence intervals (CIs) were reported. A p value less than 0.05 was considered significant. All of the analyses were performed with the statistical software packages R (http://www.R-project.org, The R Foundation).