Patients
This study retrospectively collected information on patients with patellar fracture treated in our hospital from January 2013 to December 2019. This study was approved by the Ethics Committee of the Third Hospital of Hebei Medical University. The inclusion criteria were age > 18 years with an isolated patellar fracture requiring surgical treatment. The exclusion criteria were bilateral patellar fractures, multiple fractures, open fractures, old fractures and pathological fractures, use of blood circulation pumps, autoimmune diseases, anticoagulant use within 3 months of admission, and incomplete medical records.
After admission, all patients received routine basic prophylaxis (e.g. lower limb elevation and deep breath) and chemoprophylaxis (subcutaneous injection of low molecular weight heparin, 2500-4100 IU, once daily). All patients routinely received Intermittent Pneumatic Compression Devices(IPCD)to prevent thrombosis [14, 15]. For patients allergic to LMWH, oral rivaroxaban was administered at a dosage of 10 mg once daily. Owing to the simplicity of these prophylactic measures, patients had good compliance overall.
As per our policy, all patients were not allowed to perform any weight-bearing exercises during the preoperative period and were only allowed to perform ankle pump exercises and hook-toe exercises on the bed [16]. As from the first postoperative day, patients were encouraged to do equal-length exercise and straight leg tension exercises; and depending on the tolerance, non- or partial-weight-bearing mobilization with the help of crutches was performed. At 6–8 weeks, the brace was removed after radiograph findings show no evidence of bone union. Resistance exercise was started, and complete weight-bearing mobilization was allowed.
Data collection
The data covered demographics, chronic comorbidities, and laboratory biomarkers. These include age, gender, body mass index (BMI), smoking, hypertension, diabetes, cerebrovascular disease, chronic heart disease, lung disease, any surgery history, time from injury to Doppler Ultrasound (DUS) examination, the American Society of Anesthesiologist (ASA) score; Laboratory tests included measurements of levels of total protein (TP), albumin (ALB), alanine transaminase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), high-sensitivity C-reactive protein (HCRP), creatine kinase (CK), lactic dehydrogenases (LDH), total cholesterol (TC), triglycerides (TG), glucose (GLU), D-dimer, fibrinogen (FIB), fibrinogen degradation product (FDP), and routine blood examinations included: white blood cells (WBC), neutrophils (NEU), lymphocytes (LYM), red blood cell (RBC), hemoglobin (HGB) level, hematocrit (HCT), platelets (PLT), prothrombin time (PT), prothrombin activity (PTA), international normalized ratio (INR), activated partial thromboplastin time (APTT), and thrombin time (TT).
Diagnosis criteria of thrombosis
After admission and before surgery, the patients were tested for DUS every 3 days, and if the surgery date was less than 3 days, DUS was performed a day before surgery. The "Guidelines for the Diagnosis and Treatment of Deep Vein Thrombosis (2016 3rd Edition)" issued by the Chinese Medical Association was used to diagnose and treat DVTs. Positive diagnostic criteria for DVT included (a) loss or incompressibility of the vein, (b) lumen obstruction or filling defects, (c) lack of respiratory variability in the vein segments above the knee, and (d) insufficient increase in blood flow during compression of the leg and foot. The common femoral vein, femoral vein, deep femoral vein, popliteal vein, posterior tibial vein, anterior tibial vein, and peroneal vein were assessed.
According to the thrombotic test criteria, the medical sonographer examined and reported the findings of the femoral vein trunk and the femoral deep, superficial, popliteal, tibial, and peroneal veins of both lower extremities. For patients with deep vein thrombosis, we only perform temporary fracture fixation after the thrombosis is first found, and then transfer the fracture to vascular surgery for diagnosis and treatment by professional vascular surgeons. After the condition is stable, orthopedic and vascular surgeons will evaluate the timing of surgery. Proximal DVT was defined as thrombi in the popliteal vein and above. The DVTs below the popliteal vein were considered as distal DVT. The clinical significance of thrombi in the intermuscular vein, small saphenous vein, and the great saphenous vein was relatively small; therefore, they were excluded from this study [17].
Statistical analysis
SPSS 25.0 software (IBM, Armonk, New York, USA) was used for statistical analysis. The measurement data were first explored using the Shapiro–Wilk test for their distribution status (normal or non-normal). Normal distribution data were expressed as mean ± standard deviation (Sd), and an independent sample t-test was used to compare the differences between groups. The Mann–Whitney U test was used for non-normally distributed data. Categorical variables were assessed using the chi-square or Fisher's exact tests. P values < 0.10 in the univariate analyses were further analyzed by multivariate logistic regression. P values < 0.05 were considered statistically significant for all analyses.