Stent Fracture Resistance of a Cobalt Chromium Stent

D uring the past 10 to 15 years, fractures of implanted metallic stents in various vascular and nonvascular beds have been reported. deVries et al reported fracture of a stent graft placed in the carotid artery of a 59-year-old man to treat a traumatic pseudoaneurysm 7 months after implantation.1 Carrozza reported recurrence of symptoms due to the fracture of a balloon-expandable stent placed across an aortic coarctation.2 Similarly, fractures have been reported in the coronary, subclavian, iliac, aortic, pulmonary, esophageal, tracheal, biliary, and venous stents, leading to late complications. Although stent fractures have been observed in all of the anatomic territories mentioned above, those in the superficial femoral artery (SFA) have attracted the most attention and generated the most intense scientific investigations. This may be due to the higher incidence of this problem in the SFA, caused mainly by its unique changes during various activities and positions of the lower limb as well as stent characteristics. Fractures of various SFA stents and their frequencies have been reported previously.3,4 Smouse et al analyzed biomechanical forces in the femoropopliteal arterial segment that could cause axial and bending fatigue of nitinol stents.5 Based on these biomechanical forces leading to stent fracture, disruption of stent integrity in renal arteries should be an exceedingly rare event, or is it? A review of the literature reveals that stent fractures have also been observed in the renal arteries. Bessias et al reported stent thrombosis in a 47year-old patient with a single kidney and diseased renal artery who underwent placement of a balloon-expandable stent.6 The patient presented 25 days after the procedure with renal insufficiency and uncontrolled hypertension. Angiography showed a thrombosed stent necessitating an aortorenal bypass. The explanted renal artery revealed a fractured incompletely expanded stent. Similarly, Sahin et al observed a fractured stent in a patient with mobile kidney.7 The former case report underscores the possibility of “missed” fractures in renal stents that can lead to restenosis and/or thrombosis and the latter points to a possible mechanism. In this article, we analyze the features of renal arteries that expose stents to strains and stresses that may cause strut fatigue and fracture. These include aortic pulsations and kidney motion during respiration. Craniocaudal movement and partial rotation of the kidneys during breathing causes a bend in the renal artery at or close to its point of fixation to the aorta. The impact of this bending motion on renal stents has not been sufficiently studied. We examined the renal stent bending fatigue performance and resistance of a cobalt-chromium stent (Abbott Vascular, Santa Clara, CA). STENT FRACTURES