The anterior intermuscular approaches, which include AL, ALS, and DAA, allow for implantation without damage to muscles, and they were developed to reduce postoperative bleeding, accelerate patient recovery, and improve early clinical results. The potential effect of early recovery can be expected to reduce the incidence of VTE. In this study, the incidence of VTE was evaluated before ambulation and chemoprophylaxis. The present study is, to our knowledge, the largest reported series of THA at a single institution comparing different minimally invasive intermuscular approaches that focuses on the incidence of VTE. We found that the incidence of VTE in AL was significantly higher than that in ALS and DAA.
VTE is believed to be associated with local vessel damage, decreased venous flow, and surgical hypercoagulation. Previous studies of venous blood flow during THA using a standard posterior approach demonstrated that femoral vein occlusion occurred with flexion, adduction, and internal rotation (the position of posterior dislocation) and with placement of retractors around the acetabular rim 7,8. Some studies showed that external rotation and extension, the positioning used for acetabular and femoral preparation for the anterior intermuscular approach, had no effect on femoral vein flow, as the femoral vein moves anterolaterally, which protects against compression between the proximal femur and pubic bone 7,9. Therefore, we hypothesized that the femoral vein in THA performed via the anterior intermuscular approach, including AL, ALS, and DAA, would be at a low risk for occlusive events that could increase the risk for thrombosis.
We found that the incidence of VTE in ALS and DAA is comparable, and that in AL, especially on the non-operated side, the incidence of VTE was significantly higher than that in ALS and DAA. Patients were positioned in the supine position in ALS and DAA, whereas they were positioned in the lateral position in AL. Postural changes in venous diameter due to gravity have been reported; in other words, the diameters of the right femoral vein in the right lateral position and left femoral vein in the left lateral position were reported to be significantly larger than those in the supine position 10. Hence, there is a possibility that the femoral venous flow of the non-operated side in the lateral position may be slower than that in the supine position, resulting in a higher incidence of VTE.
There is a report that the right femoral vein may be at higher risk for VTE in the right lateral position than in the supine position 10. According to this report, there are two possible causes. First, the inferior vena cava may be compressed by abdominal viscera in the right lateral position, resulting in decreased blood return from the lower extremities. Second, sympathetic tone is lower in the right decubitus position 11, and peripheral venous dilatation may occur, which may decrease venous return and velocity. However, in the current study, a difference in the incidence of VTE between the right leg in the right decubitus position (11%: 5 of 44) and the left leg in the left decubitus position (11%: 6 of 56) was not seen in AL.
On the operated side, there was a tendency toward an increased incidence of VTE in AL compared to that in ALS and in DAA. The position itself, placed in approximately 10 degrees of flexion and 60 degrees of external rotation for the acetabular preparation and 120 degrees of external rotation and maximal extension for femoral preparation for the anterior intermuscular approach, is equivalent among these approaches, and it has been reported to be safe for femoral venous blood flow in 100% of patients during acetabular exposure and 80% of patients during femoral exposure (9). We speculate that decreased blood return from the lower leg, due to lowering the operated leg toward the floor in AL, may be a cause of the higher VTE incidence 12 compared to that in the supine position.
The placement of an anterior single-pronged Homan-like retractor over the anterior wall during acetabular preparation in the anterior approach is reported to be a cause of consistent occlusion of the femoral vein 9, whereas positioning the leg for acetabular and femoral preparation did not lead to occlusion of the femoral vein. In the present study, we did not measure retraction time. However, the operative time was not significantly different between the groups, and we believe the period of retractor placement was thus not significantly different between the approaches.