Covered vs Bare Metal Stents for Iliac Disease: What the Evidence Shows

The question of whether a covered stent is worth its extra cost over a bare metal stent for iliac artery occlusive disease has been asked, tested, and revisited for well over a decade. It’s a fair question. Covered stents cost more, require a larger delivery profile in most cases, and add a graft material that bare stents don’t need. The clinical case for using one anyway rests on a fairly small number of trials, so it’s worth setting out what they actually found rather than relying on general impressions of “covered is better”.

The COBEST trial: still the primary evidence base

The Covered Versus Balloon Expandable Stent Trial, generally known as COBEST, remains the only randomised controlled trial directly comparing covered and bare metal stents in iliac occlusive disease, which is worth keeping in mind whenever a confident claim is made in either direction. The trial randomised 168 iliac arteries in 125 patients with severe aortoiliac occlusive disease to receive either a covered balloon-expandable stent or a bare metal stent, with outcomes assessed by TASC classification, a system that grades lesion severity and complexity from A (simple, focal) through to D (extensive, complex, often bilateral or occlusive).

The headline finding at 18 months was that aortoiliac lesions treated with a covered stent were significantly more likely to remain free from binary restenosis than those treated with a bare metal stent. But the more clinically useful finding sits in the subgroup analysis: covered stents showed a significant advantage specifically in TASC C and D lesions, the more extensive and complex end of the classification, while TASC B lesions showed no significant difference between the two. In other words, the trial doesn’t support “covered stents are simply better”, it supports “covered stents earn their advantage in more complex disease, and for straightforward TASC B lesions, a bare metal stent performs comparably”.

The five-year follow-up: does the advantage hold?

A retrospective analysis of the COBEST cohort at five years addressed the obvious next question: does an 18-month advantage actually last? It found that covered stents maintained significantly higher patency than bare metal stents at 18, 24, 48 and 60 months, with covered stent patency at 74.7% versus 62.5% for bare metal stents at the five-year mark. Patients who received a covered stent also required fewer repeat revascularisation procedures over the follow-up period. Notably, the choice of stent type didn’t affect the rate of major limb amputation, an important caveat against overstating the clinical stakes of the decision.

What more recent trials have added

COBEST isn’t the only word on the subject, and the picture has become more nuanced since. The DISCOVER trial, a more recent randomised comparison focused specifically on the common iliac artery, didn’t find an overall significant difference between covered and bare metal stents at two years. However, its subgroup analysis showed a trend toward better outcomes with covered stents in TASC C and D lesions specifically, consistent with the COBEST pattern, even though the subgroup was too small (46 limbs) to reach statistical significance on its own. Separately, real-world registry data, including the BOLSTER multicentre study looking at balloon-expandable covered stents specifically, has broadly supported the safety and patency profile seen in the trial data, in a less controlled but larger and more representative patient population.

Put together, the evidence base currently points in a consistent direction without being definitive: covered stents appear to offer a genuine, durable patency advantage in more complex TASC C and D iliac disease, where the vessel involvement, calcification, or bilateral extent makes durability harder to achieve with a bare metal stent alone. For simpler TASC B lesions, the case for paying the premium for a covered stent is considerably weaker, and a bare metal stent remains a reasonable, well-supported choice.

Why the covered stent might still be worth it even where the difference isn’t dramatic

Beyond raw patency figures, covered stents carry a practical advantage that trial endpoints don’t always capture well: they provide a degree of protection against vessel wall injury during the procedure itself, including the ability to manage a perforation or dissection immediately with the device already in place, rather than needing to escalate to a separate covered stent as a rescue measure. For operators working on more complex, calcified, or previously treated iliac anatomy, that margin of safety during the case itself is often as relevant to the stent choice as the published patency curves.

What this means in practice

The decision in most departments comes down to lesion complexity rather than a blanket policy either way:

• TASC B lesions: the evidence doesn’t show a significant advantage for covered stents. A bare metal stent is a reasonable, cost-effective first choice.
• TASC C and D lesions: the evidence, across both COBEST and the DISCOVER subgroup analysis, consistently favours covered stents for durability and freedom from restenosis.
• Complex or heavily calcified anatomy where perforation risk is a real procedural concern: the covered stent’s ability to manage a vessel injury in situ is a practical factor worth weighing alongside the trial data.

Our iCover balloon-expandable covered stent range and Restorer peripheral stent range from iVascular cover both ends of this decision, and our team can talk through sizing and case-specific considerations for iliac procedures. For a broader look at how covered stents are used across iliac disease more generally, see our earlier article on the role of covered stents in treating iliac disease. Get in touch with any procurement or case-specific questions.

Frequently asked questions

Are covered stents better than bare metal stents for iliac disease?

It depends on lesion complexity. The COBEST trial found covered stents offer a significant patency advantage in TASC C and D lesions, but showed no significant difference from bare metal stents in less complex TASC B lesions.

What is the COBEST trial?

COBEST (the Covered Versus Balloon Expandable Stent Trial) is a randomised controlled trial that compared covered and bare metal balloon-expandable stents in 168 iliac arteries across 125 patients with aortoiliac occlusive disease, with outcomes reported at 18 months and again at five years.

Does the covered stent advantage last long term?

Yes. A five-year follow-up of the COBEST cohort found covered stents maintained significantly higher patency than bare metal stents throughout the follow-up period, and patients with covered stents required fewer repeat revascularisation procedures.

Do covered stents reduce amputation risk compared with bare metal stents?

The COBEST five-year data found no significant difference in major limb amputation rates between covered and bare metal stents, despite the patency advantage seen with covered stents. The clinical benefit is primarily in restenosis and reintervention rates rather than limb salvage.

What does TASC classification mean for stent choice?

TASC (TransAtlantic Inter-Society Consensus) classification grades iliac lesion complexity from A to D. The trial evidence for covered stents is strongest for TASC C and D lesions; for simpler TASC B lesions, bare metal stents perform comparably.