Analyses for the primary outcome
VTE
PULMONARY EMBOLISM, REGRESSION, DEEP VENOUS THROMBOSIS
The rate of symptomatic VTE for the entire cohort was described overall and categorized via type (pulmonary embolism or deep venous thrombosis) for each prophylaxis group. The median time to VTE diagnosis for each group was also described. Univariate analyses were used to identify predictors of VTE. Fisher’s exact test was used for categorical, dichotomous variables and logistic regression for categorical non-dichotomous variables and for continuous variables, with the outcomes reported using a point estimate (odds ratio – OR) and a 95% confidence interval.Factors identified on univariate analysis with a p-value < 0.25 were entered into a backwards, stepwise multivariable logistic regression model (using the Akaike information criterion – AIC) to identify independent predictors of symptomatic VTE. As the exposure of interest, type of VTE prophylaxis was forced into the multivariable regression model. Known potential confounders of VTE (age, sex, BMI, smoking status, joint replaced and prior history of VTE) were forced into the model regardless of whether they produced a p-value of < 0.25 on univariate analyses.Multiple imputation using chained equations was used to address missing values and model averaging from each individual imputed dataset, with pooled results was used for the multivariable analysis. As the objective of the study was to investigate symptomatic VTE only, routine DUS was omitted from the multivariable regression model.