This single-center retrospective cohort study was conducted based on Strengthening the Reporting of Observational Studies in Epidemiology statement.

Our study was approved by the institution’s ethics committee, and the requirement for informed consent was waived due to the retrospective nature of the study.

We included 1119 cases of hip fractures treated between October 2010 and December 2020. The exclusion criteria were as follows: (1) patients ≤ 65 years of age; (2) no postoperative duplex ultrasonography; (3) no body mass index (BMI) data; and (4) simultaneous bilateral hip fractures.

Preoperative: Patients were encouraged to wear elastic stockings on both lower limbs. Automatic ankle joint movement was encouraged to the maximum extent possible.

Intraoperative: Intermittent pneumatic compression device worn on the healthy side.

Postoperative: Intermittent pneumatic compression device worn on both sides.

Patients without contraindications were treated with anticoagulants. On postoperative day 5, DVT of both the lower extremities was evaluated using duplex ultrasonography.

Distal DVT was defined as a thrombus in the tibial, peroneal, soleus, or gastrocnemius vein. Proximal DVT was defined as a thrombus in the popliteal vein or a vein proximal to the popliteal vein [15]. If distal and proximal DVT occurred together, we classified it as proximal DVT [16]. Based on medical records, we examined factors that might influence the development of DVT. Factors influencing DVT were age at injury, sex, BMI, fracture type, operative technique, time from injury to surgery, time from surgery to echo, and postoperative anticoagulation therapy, based on previous reports [17].

It has been reported that surgery within 48 h of admission improves outcomes [17]. However, there are cases where this time elapses between injury and hospitalization. We examined patients who underwent surgery within 48 h of injury and those who underwent surgery after this duration.

Patients with and without VTE were classified into the V and NV groups, respectively. Patients with and without proximal DVT were classified into the PD and NPD groups, respectively.

Factors that may influence the development of DVT were compared in univariate and multivariate analyses between the V and NV groups and between the PD and NPD groups.

In univariate analysis, the Mann–Whitney test was used for numerical data and Fisher's exact test for categorical data. Additionally, the risk factors for the development of VTE and proximal DVT were analyzed using logistic regression analysis to test whether the duration of the surgical waiting period was a risk factor.

All p values were two-sided, and results were considered statistically significant at p values < 0.05. All statistical analyses were performed using EZR (Saitama Medical Center, Jichi Medical University, Saitama, Japan), a graphical user interface for R (The R Foundation for Statistical Computing, Vienna, Austria). It is a modified version of the R software focusing on statistical functions frequently used in biostatistics.