- Patient selection
Approved by the institutional review board, from January 2006 to December 2017, PJI patients who underwent revision surgery in our center were enrolled. Inclusion criteria: 1) Tsukayama type IV PJI cases; 2) patients whose revision surgeries were performed with an antibiotic-impregnated cement spacer and who underwent regular follow-up; and 3) patients with complete medical data. Exclusion criteria: 1) patients without regular follow-up data (at least two years) or timely medication and with poor compliance; 2) patients whose clinical outcomes were affected by infectious diseases in other parts of the body and patients who had immunosuppressive disease or malignant tumors; and 3) patients with non-PJI-related death. A diagnosis of PJI was made according to the American Society for Musculoskeletal Infection (MSIS) criteria for PJI. With the approval of the Ethics Committee of our hospital, 62 PJI cases were included with an average age of 65.13 ±9.94 (39-88) years; there were 26 males and 36 females: 38 hips and 24 knees (summarized in Table 1). The mean follow-up time was 45.12 ±6.31 months.
- The process of revision surgery and preparation of joint spacers.
The revision surgeries were performed by the same medical team. Sufficient synovial fluid was obtained pre- and intraoperatively, and white blood cell (WBC) counts, polymorphonuclear (PMN) examinations, microbial cultures and drug sensitivity tests were routinely performed. At least 5 samples of periprosthetic tissues were obtained intraoperatively for microbial culture and intraoperative pathological examination. After removal of the prosthesis, debridement was performed using hydrogen peroxide, povidone iodine and saline, and then antibiotic-impregnated joint spacers were prepared.
For hips, two types of joint spacers were used 13,14. For type I, 1-2 Kirschner wires with a diameter of 5 mm that were bent to approximately 130° in advance were used as stents, which were placed in a silicone mold imitating the shape of the joint, embedded with antibiotic-impregnated cement and molded under pressure (Fig1AB). For type II, 105 mm femoral stem, 28 mm femoral head and 32 mm femoral neck (CM-CZ; AK Medical, Beijing, China) were used as scaffolds, which were embedded with antibiotic-impregnated cement and molded under pressure (Fig 1 CD). For knees, two types of spacers were also used 13-15: for type I, an aseptic silicone mold imitating the joint shape was used, and a joint-like spacer was made intraoperatively (Fig 1 EF); for type II, the removed femoral end prosthesis was washed, soaked in povidone iodine solution and resterilized, and the resterilized tibial prosthesis was used or replaced with a new polyethylene tibial component (Fig 1 GH). The choices of spacers were determined by patients’ wishes (for those with higher mobility needs, type Ⅱwas chosen), pathogenic microorganism (for those who infected with fungi or multi-drug resistant bacteria, type Ⅰwas chosen for higher local antibiotic concentration, sustained local antibiotics release) and surgeons’ judgements. The antibiotics used in the antibiotic-impregnated joint spacer were selected according to the microbial culture and drug sensitivity test results. For those who had negative microbial culture results, vancomycin + ceftazidime (4.0 g vancomycin + 4.0 g ceftazidime per 40 g bone cement) was empirically used.
After joint spacers were implanted, patients were followed up regularly. When infection was eliminated, prosthesis reimplantation was considered according to patients’ wishes, economic condition, and surgeons’ judgements. For those with multiple underlying disease, persistent infection, and large bone defects, the reimplantation was considered to be tough. Patients who did not undergo prosthesis reimplantation were grouped into "destination joint spacers" group.
For those who underwent prosthesis reimplantation, after infection elimination, the joint was incised along the original surgical incision, and joint spacers were thoroughly removed with necrotic granulation tissue, scar tissue and cement debris. After washing with a large amount of hydrogen peroxide, povidone iodine and saline, the new prosthesis was reimplanted. Those who have undergone prothesis reimplantation were grouped into "temporary spacers" or "two-stage revision" group.
- Follow-up postoperatively
The administration of antibiotics was based on the microbial culture and drug sensitivity test results, while those with negative microbial culture results were empirically treated with vancomycin. After receiving intravenous antibiotic treatment for 2 to 4 weeks, oral antibiotics were replaced. Patients were followed regularly postoperation. The patient's age, sex, BMI, laboratory test results (such as CRP, ESR, synovial fluid WBC, and PMN%), Charlson comorbidity index (CCI), reasons for joint spacer retention, etc., were recorded. The diagnosis of infection recurrence was based on the symptoms, signs, laboratory tests and images, which were judged by at least 2 orthopedic experts and 1 infectious disease expert. Harris hip score (HHS) and knee society score (KSS) were used for functional evaluation, a Doppler ultrasonography of the lower limb veins was performed for all patient in first three months post-operation and whenever thrombosis of lower extremities was suspicious for complication evaluation. The primary outcome was infection elimination, and complication was the second outcome.
- Statistical analysis.
All statistical analyses were performed using SPSS 20.0. The enumeration data were expressed as the mean ± standard deviation and compared by Student’s t-test, while measurement data were expressed by rate and compared by the chi-square test. And complications odds ratio of different type spacers was calculated. P ≤ 0.05 was considered statistically significant.