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

ABSTRACT

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.