Although pharmacological prophylaxis is recommended in hip fracture patients, the incidence of DVT remains high. The incidences of postoperative DVT and PNO-DVT in inpatients after intertrochanteric fracture surgery were 11.5% (202 of 1751 patients) and 7.4% (123 of 1672 patients), respectively. Patients with PNO-DVT accounted for 60.9% of those with postoperative DVT. and 82.1% of DVTs were diagnosed within 8 days after surgery. While, the diagnosis of the DVT might be delayed for the examinations were performed every 3 to 5 days after surgery. In addition, the results of multivariate logistic regression analyses demonstrated that age > 70 years, duration of surgery > 197 mins, general anesthesia and number of comorbidities > 3 were independent risk factors for the development of PNO-DVT.
The 11.5% incidence of postoperative DVT was similar to that of DVT in previous studies. In their study of DVT in hip fractures, Eriksson et al 19 found that the prevalence of DVT after hip fractures was 14% within postoperative day 11. Wang et al 20 detected the incidence of postoperative DVT in patients with intertrochanteric fractures. They found that the prevalence of DVT after intertrochanteric fracture surgery was 9.94% in 311 patients.
Patients with postoperative DVT could be divided into those with preoperative DVT and those without preoperative DVT, and those without preoperative DVT were defined as PNO-DVT in this study. In the present study, the incidence of PNO-DVT was 7.4% (123 of 1672 patients), which accounted for 60.9% of postoperative DVT. In addition, 39.1% of those patients had preoperative DVT, which was excluded from the statistical analysis. For patients with preoperative DVT, the dosage of LMWH and physical prophylaxis might be different from those of patients without preoperative DVT. In addition, their coagulation function might vary. All of the above might result in possible differences in risk factors for postoperative DVT between patients with PNO-DVT and patients with preoperative DVT. Moreover, a better understanding of the risk factors for PNO-DVT is conducive to taking more measures to prevent the development of PNO-DVT.
Four independent predictive factors for PNO-DVT in inpatients after intertrochanteric fracture surgery were identified in this study. As an independent risk factor for DVT, advanced age has been reported in previous studies. In this study, age > 70 years was a cut-off value for the development of PNO-DVT detected by ROC curve analysis. Shahi et al reported a risk factor for the development of in-hospital VET after hip surgery21. These researchers demonstrated that age > 70 years (OR: 1.3, 95%, CI: 1.1–1.4) was an independent factor for increasing the risk of developing in-hospital VET, which was consistent with our study. Park et al also reported that age > 60 was an independent risk factor for the development of DVT12. Advanced age has always been associated with frailty and additional comorbidities. Frailty is a common status in patients with intertrochanteric fractures, especially in patients with advanced age, and can seriously affect their quality of life22. Anemia is a common condition in patients with advanced age that has been demonstrated to increase the risk of DVT23. In addition, immobilization tends to be longer in patients with advanced age, which is one of the primary reasons for the development of DVT24.
The hypercoagulation state is well known as a main factor promoting thrombosis2. Surgery is a significant factor for the formation of DVT after acute trauma in terms of the introduction of the hypercoagulability state5,25. It has been reported that approximately 15% of all VETs are surgery-related26.
The surgery duration was 197 mins according to the results of the ROC curve analysis.
Multivariate logistic regression analyses revealed that a duration of surgery > 197 mins was an independent factor for the risk of PNO-DVT. Blood loss increasesd with a prolonged duration of surgery. Riha et al found that blood loss was an important factor in promoting the hypercoagulability state in their study27
. Their study showed that blood loss was associated with an increase in the risk of DVT. Zhang et al studied the incidences of DVT before and after surgery in in-hospital patients with hip fractures and found that blood loss was correlated with the formation of postoperative DVT6
. Therefore, a longer duration of surgery might be associated with the developing of DVT for leading to a higher level of coagulation.
The optimal anesthetic modality in hip fracture surgery remains controversial. The choice of anesthesia modality in hip fracture surgery often depends on the preference of the surgeon or the anesthesiologist28. Previous studies have reported that the anesthesia modality in hip fracture surgery plays an important role in the occurrence of postoperative complications29,30. Some studies have demonstrated that spinal anesthesia is superior to general anesthesia in preventing DVT, urinary tract infection, blood loss, superficial wound infection and overall complications13,31. The results of this study were the same as those of a previous study on the association between anesthesia and DVT. The percentage of patients with general anesthesia was 53.7% (66 of 123 patients) in the DVT group, whereas the percentage of patients in the without-DVT group was 41.8%. Significant differences in anesthesia modality were found between the two groups (p = 0.011). In addition, the present study demonstrated that the risk for developing DVT in patients with general anesthesia after intertrochanter fracture surgery was increased 1.558-fold compared with that in patients with spinal anesthesia. The explanations for this phenomenon might be that general anesthesia increases the length of hospital stay32. Further studies should be conducted to explore the specific mechanism of anesthesia and DVT.
There were some strengths in our study. Few studies investigated the risk factors for PON-DVT, and this study excluded the patients with preoperative DVT. What’s more, the data of this study were based on a prospective database, and approximately 80 factors were analyzed in this study. All above would help increase the reliability and accuracy of the results in present study. however, our study did have some limitations. First, all the data were extracted from one hospital. Additionally, this study was a single-center study, which was limited by its inherent defects. Further multicenter randomized controlled trials are warranted. Second, some comorbidities, such as varicose veins and defects of the coagulation system, were not discussed in our study.