Diagnosis and classification of DVT

DVT was diagnosed in accordance with the Guidelines for the Diagnosis and Treatment of Deep Vein Thrombosis proposed by Chinese Medical Association [13]. According to institutional policy, hip fracture patients are asked to receive duplex ultrasonography (DUS) examination for potential DVT of the bilateral extremities at admission, subsequently every 3–7 days and when any symptoms suggestive of DVT presented, and the veins involved may be any one or any combined (common femoral vein, superficial femoral vein, deep femoral vein, popliteal vein, anterior tibial vein, posterior tibial vein or peroneal vein). The criteria for DUS diagnosis of DVT are: loss of or non-compressibility, lumen obstruction or filling defect, lack of respiratory variation in above-knee vein segments and inadequate flow augmentation to veins of calf and foot with compression maneuvers. Based on DUS results, the patient would be given therapeutic or prophylactic thromboembolic agents, thereafter, second or further DUS scans are conducted until the operative procedure.

Depending on the location of the thrombus, we classified patients into two groups: distal DVT group where patients had any thrombus at anterior tibial vein, posterior tibial vein, peroneal vein solely or combined, and proximal DVT group where patients had any thrombus at popliteal or femoral vein, regardless of having co-existing distal DVTs. It is of note, isolated thrombosis solely located in the intramuscular veins (e.g. soleal or gastrocnemius vein) is excluded from this study, due to their less clinical significance [14].