The study was reported in accordance with the STROCSS (Strengthening the Reporting of Cohort Studies in Surgery) guidelines. It was designed as a retrospective study and approved by the ethics committee of the 3rd Hospital of Hebei Medical University.
Inclusion and exclusion criteria
Between January 2016 to June 2019, patients who underwent surgical treatment for acute ankle fractures in our hospital were included. The baseline characteristics and complications during hospitalization were obtained from the patient's medical records. Inclusion criteria were: patients aged 18 years or older, definite diagnosis of ankle fracture, surgical treatment (osteosynthesis) and complete data available in medical records. Exclusion criteria were: pathological (metastatic) or old fracture (> 3 weeks since occurrence), open fracture, concurrent fractures in other locations, conservative treatment, incomplete medical records, current use of heparin, low molecular weight heparin (LMWH) or other anticoagulants due to chronic comorbidities, and preoperative diagnosis of DVT.
After admission, all patients received basic thromboprophylaxis, consisting of chemical (low molecular weight heparin (LMWH), 2500-4100 IU once daily, subcutaneous injection) and elevation of the injured lower extremity for each patient.
Diagnosis of DVT
DVT was diagnosed in accordance with the Guideline for the Diagnosis and Treatment of Deep Vein Thrombosis (3rd edition) proposed by Chinese Medical Association . Ultrasound report was used to obtain the diagnostic information of DVT. During the postoperative hospitalization stay, in patients with lower limb swelling, pain, tenderness in the rear and/or inner thighs, DVT was confirmed by duplex ultrasound: deep venous lumen obstruction or filling defect. Routine scanning was performed for the femoral common vein, superficial and deep femoral vein, popliteal vein, posterior and anterior tibial vein, and peroneal vein of bilateral lower extremities. Superficial or intermuscular vein thrombosis (soleal or gastrocnemius vein thrombosis) was excluded, due to their relatively less clinical significance [16, 17].
Electronic medical records (EMR), picture archiving and communication system (PACS), operation reports were inquired for relevant data. The demographic data included age, gender, residence (urban or rural), body mass index (BMI), cigarette smoking and alcohol consumption. The co-morbidities included hypertension, diabetes, ischemic heart disease, previous history of any surgery and history of allergies to any medications, all of which were self-reported by patients. Fracture and surgery-related data included: fracture location (uni-, bi-or trimalleolar fracture), injury mechanism (low- or high-energy trauma), accompanied dislocation, concurrent fracture, preoperative interval (between fracture occurrence and operation), American Society of Anesthesiologists (ASA) classification, anesthesia type, type of fracture reduction (open or closed), prophylactic use of antibiotics, surgical duration, bone graft, fixation type, intraoperative blood loss, perioperative blood transfusion, and postoperative use of drainge. The BMI (kg/m) was divided using the criteria recommended by the Chinese working group on obesity: normal (18.5-23.9), underweight (<18.5), overweight (24.0-27.9) and obesity (>=28.0). Low-energy injury was defined as an injury caused by a fall from a standing height, and others such as fall from a height, motor accidents were high-energy injury.
The biomarkers from preoperative laboratory tests included total protein (TP) level, albumin (ALB) level, fasting blood glucose (FBG) level, preoperative red blood cell (RBC) count, white blood cell (WBC) count, neutrophile (NEUT) count, lymphocyte (LYM) count, neutrophile/lymphocyte rate (NLR), hemoglobin (HGB) level, haematocrit (HCT), platelet (PLT), red blood cell distribution width (RDW), serum total cholesterol (TC) level, triglyceride (TG) level, low density lipoprotein (LDL-C) level, high density lipoprotein (HDL-C) level, very low-density lipoprotein (VLDL) level and D-dimer level. If patients had multiple laboratory tests before when DVT was diagnosed, laboratory tests closest to the diagnostic time point were chosen for data analysis.
Continuous variables were expressed by mean and standard deviation (SD), and were evaluated by student-t test or Mann Whitney-U test. The categorical data were expressed as number and percentage (%), and were evaluated by chi-square or Fisher's exact test. Multivariate logistics regression model was used to identify the independent risk factors associated with occurrence of DVT, using the stepwise backward elimination method. Variables with p<0.10 were retained in the final model, and the correlation strength is indicated by odd ratio (OR) and 95% confidence interval (95%CI).The statistical test level was set as p<0.05. Hosmer-lemeshow (H-L) test was used to evaluate the fitting degree of the final model, and p>0.05 represented the acceptable result. SPSS23.0 was used to perform all the tests (IBM, armonk, New York, USA).