Data used in this study were extracted from the database of Surgical Site Infection in Orthopaedic Surgery (SSIOS), in which a prospective method was used to collect data on patients who underwent orthopaedic surgeries between October 1 2014 and December 31 2018. In SSIOS study, surveillance of surgical site during hospitalization and telephone follow-up after discharge were conducted to identify surgical site infections.
In this study, the inclusion criteria were all adult patients (≥ 18 years) with closed tibial plateau fractures treated with ORIF. Multiple trauma patients were also included. Exclusion criteria were under 18 years of age, open fractures, pathological fractures caused by other diseases, treatment with external fixation or conservative method, incomplete medical data, patients lost to follow-up, and fractures around the prosthesis after knee replacement.
In order to accurately analyze the factors of postoperative infection, from the beginning we collected as much information as possible about the patient, including patients’ demographics information, the preoperative evaluation, and the various indicators during the operation. We set up a well-trained team to collect the detailed information of each patient every day. Investigators visited the ward regularly, followed the patients closely, questioned them, looked at their medical records and charts, recorded the variables of interest, and examined the suture site for signs of infection since the day after the surgery. After discharge, all patients underwent regular telephone follow-up at postoperative 3, 6, 12 months to determine the presence of SSI.
Data Collection Of Variables
Patients’ demographics information including age, gender, height, weight, chronic diseases (diabetes mellitus, hypertension, cerebrovascular disease, chronic heart disease), living places (rural or urban), history of any surgery, allergy to any medications, smoking status, alcohol consumption were extracted and documented.
Body Mass Index (BMI) was divided into four groups using Chinese standards: normal, 18.5–23.9; underweight, < 18.5; overweight, 24-27.9; obesity and morbid obesity, ≥ 28.
Characteristics of fractures included injury mechanism (low or high-energy), side involved, combined injuries and fracture classification (Schatzker classification system). Fall from a standing height was defined as a low-energy injury, and fall from a height, traffic accident, and a sports injury was defined as a high-energy injury.
Surgery-related variables included ASA grade (American Society of Anesthesiologists), preoperative duration, anesthesia pattern, operative duration, fixation type, intraoperative blood loss, intraoperative blood transfusion, bone grafting, intraoperative and postoperative intravenous use of antibiotic. Preoperative duration was defined as time from injury to surgery, and was divided into two groups: 1, ≤ 7 days and 2,༞7 days. Anesthesia pattern was divided into regional anesthesia and general anesthesia. Operative duration was also divided into two groups: 1, ≤ 120 minutes and 2,༞120 minutes. Intraoperative blood loss was divided into two groups: 1, ≤ 400 ml and 2,༞400 ml. Bone grafting pattern was divided into autograft and allograft. Prophylactic antibiotics were administered intravenously 30 minutes before surgery according to guidelines.
We recorded the values of pre-operative laboratory examinations and divided them into normal, higher or lower than normal. These variables included platelet (PLT), albumin/globulin (A/G), alanine transaminase (ALT), neutrophils (NEUT), white blood cells (WBC), red blood cell (RBC), albumin (ALB), total cholesterol (TC), aspartate aminotransferase (AST), low density lipoprotein (LDL-C), hematatocrit (HCT), lactate dehydrogenase (LDH), monocytes (MON), mean corpuscular hemoglobin (MCH), lymphocytes (LYM), hydroxybutyrate dehydrogenase (HBDH), triglyceride (TG), high density lipoprotein (HDL-C), very low-density lipoprotein (VLDL), γ-glutamyl transpeptidase (GGT), mean corpuscular volume (MCV), osmotic pressure (OSM), indirect bilirubin (IBIL), serum urea (UREA), uric acid (UA), hemoglobin (HGB), red cell distribution width (RDW), hypersensitive c-reactive protein (HCRP), platelet distribution width (PDW), glucose (GLU), mean corpuscular hemoglobin concentration (MCHC), total protein (TP), globulin (GLOB), anion gap (AG), aspartate total bilirubin (TBIL), direct bilirubin (DBIL), alkaline phosphatase (ALP), cholinesterase (CHE), total bile acid (TBA).
Definition Of SSI
SSI was defined based on the standards of Center for Disease Control (CDC). Fascia or muscle infections, skin dehiscence or persistent wound secretions, visible abscesses or gangrene requiring surgical debridement and implant exchange or removal were considered deep SSI. Infections limited to the skin of the surgical site, not exceeding the depth of the subcutaneous tissue, with common surgical incision problems (redness, swelling, pain) that could be cured by oral or intravenous antibiotics are considered superficial infections.
For continuous variables, Student t-test and Mann-Whitney U-test were used (depending on whether the value of the variable is normally distributed), and the significance was p < 0.05. First, a univariate logic analysis was used to evaluate the relationship between each categorical variable and SSI. Then the variables that were tested as significant in the univariate analyses to predict SSI were included in the multivariate logistic regression analysis model, and the independent predictors of SSI were finally determined. The goodness of fit of the model was tested using Hosmer-Lemeshow. p > 0.05 was an acceptable goodness of fit.