A recent multicentre, prospective study has found that stent deformations are greater in the common iliac vein with higher levels of hip flexion, as well as in iliofemoral veins with hyperextension at the superior ramus of the pubis.
Their results suggest anatomic positioning and physical activity type/level can cause device fatigue which must be considered for “careful” anatomic placement, activity modification and future device design and evaluation.
Central to their investigation, lead study author Christopher P Cheng (Stanford University, Stanford, USA) and colleagues set about characterising deformations of venous stents implanted into common iliac veins (for non-thrombotic 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.
Patients who were treated with iliofemoral venous stents were recruited from three centres and imaged with two orthogonal two-dimensional (2D) projection X-rays. Stents in the common iliac veins and iliofemoral veins crossing the hip joint were imaged in 0°/30°/90° and -15°/0°/30° hip positions. Subsequently, using the X-ray images, the researchers constructed three-dimensional (3D) geometries of the stents for each hip position and diametric, employing these to quantify bending deformations between those positions.
Of their results, Cheng et al note that 12 patients who received iliac vein stents experienced approximately two-fold more local diametric compression with 90° hip flexion, compared to 30° flexion. Continuing, they state those with iliofemoral vein stents crossing the hip joint experienced “significant” bending in the hip hyperextension (-15°) but not with hip flexion. Furthermore, Cheng and colleagues observed that in both anatomic locations, maximum local diametric and bending deformations were in proximity to one another.
The researchers’ observations conclude that 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.
Reflecting on this correlation, Cheng et al believe that device fatigue may be influenced by the type and extent of patient physical activity, alongside anatomic positioning. To this end, they underscore the potential benefits of activity modification and invite caution when planning an implantation strategy on a case-by-case basis. Additionally, they posit that the proximity of maximum diametric and bending deformations means that simultaneous multimodal deformations need to be considered for device design and evaluation.
