Stent deformations in the common iliac and iliofemoral veins as a result of hip flexion and extension.

OBJECTIVE: In the present study, we characterized deformations of venous stents implanted into common iliac veins for nonthrombotic iliac vein lesions and iliofemoral veins for deep vein thrombosis due to hip movements commensurate with everyday activities such as walking, sitting, and stair climbing. METHODS: Patients treated with iliofemoral venous stents were recruited from three centers and underwent imaging with two orthogonal two-dimensional projection radiographs. Stents in the common iliac veins and iliofemoral veins crossing the hip joint were imaged with the hip in 0°, 30°, 90° and -15°, 0°, and 30° positions, respectively. Using the radiographs, the three-dimensional geometries of the stents were constructed for each hip position, and the diametric and bending deformations between those positions were quantified. RESULTS: Twelve patients were included, and the findings showed that the common iliac vein stents experienced approximately twofold more local diametric compression with 90° hip flexion compared with 30° flexion. Also, iliofemoral vein stents crossing the hip joint experienced significant bending with hip hyperextension (-15°) but not with hip flexion. In both anatomic locations, maximum local diametric and bending deformations were in proximity with each other. CONCLUSIONS: Stents implanted in the common iliac and iliofemoral veins exhibit greater deformation during high hip flexion and hyperextension, respectively, and iliofemoral venous stents interact with the superior ramus of the pubis during hyperextension. These findings suggest that device fatigue could be influenced by the type and level of patient physical activity, in addition to anatomic positioning, opening up the potential benefit of activity modification and the use of a careful implantation strategy. The proximity of maximum diametric and bending deformations means that simultaneous multimodal deformations should be considered for device design and evaluation.

The biomechanical impact of hip movement on iliofemoral venous anatomy and stenting for deep venous thrombosis.

BACKGROUND: Stenting of the iliofemoral vein may be an effective treatment to improve post-thrombotic symptoms. Iliofemoral vein stents have requirements different from those of lower extremity artery stents, and there is a paucity of literature regarding the biomechanical motion of the iliofemoral vein. METHODS: In a novel cadaveric model, stents were bilaterally inserted into the veins in the iliofemoral region. The veins were pressurized and underwent computed tomography angiography at various hip angle positions. In addition, 21 patients with iliofemoral vein disease had supine computed tomography angiography before and after stenting. The stents and vasculature were reconstructed into three-dimensional geometric models to quantify stent deformations and the interaction between the iliofemoral vein, inguinal ligament, and pubis bone due to hip flexion-extension. RESULTS: In the cadavers, from supine to 30 to 45 degrees and 50 to 75 degrees of hip flexion, iliofemoral vein stents became less compressed (4.5% minor diameter expansion), and the inguinal ligament was separated from the iliofemoral veins by 1 to 3 cm in all hip positions. In the patients, the pubis compressed 47% of femoral veins; 78% were within 3 mm of the pubis. There was also evidence of contrast-enhanced flow disruption at the superior ramus. CONCLUSIONS: The cadaver and clinical evidence shows that contrary to widely accepted dogma, the common femoral vein is not compressed by the inguinal ligament during hip flexion but rather by the superior ramus of the pubis during hip extension, which may have an impact on future stent design and influence deep venous thrombosis treatment strategies.