JACC: CARDIOVASCULAR INTERVENTIONS VOL. 17, NO.

20, 2024

ª 2024 BY THE AMERICAN COLLEGE OF CARDIOLOGY FOUNDATION

PUBLISHED BY ELSEVIER

STATE-OF-THE-ART REVIEW

Knuckle Guidewires to Create

Dissections in Chronic Total Occlusion
Percutaneous Coronary Intervention
Position Statement

Stéphane Rinfret, MD, SM,a Glen A. Henry, MD,a Jaikirshan J. Khatri, MD,b Kambis Mashayekhi, MD, PHD,c,d
Khaldoon Alaswad, MD,e Lorenzo Azzalini, MD, PHD, MSC,f Luiz F. Ybarra, MD, PHD, MBA,g
Ram Vijayaraghavan, MD,h,i Jarrod D. Frizzell, MD,j Alexandre Avran, MD,k Margaret B. McEntegart, MD,l
William L. Lombardi, MD,f J. Aaron Grantham, MD,m Emmanouil Brilakis, MDn

ABSTRACT

Dissection and re-entry techniques are essential to achieve safe and effective chronic total occlusion recanalization.
Several studies have demonstrated similar outcomes following extraplaque stenting compared with intraplaque stenting.
Dissection techniques most often involve the use of knuckled wires to progress within and beyond the chronic total
occlusion segment. In this expert consensus document, the authors compare the properties of different polymer-jacketed
wires for their use in dissection techniques. The authors also describe 2 principal knuckle wire behaviors, the rolling and
the traveling knuckles. Finally, several adjunctive techniques for safer dissection are described.
(JACC Cardiovasc Interv. 2024;17:2411–2424) © 2024 by the American College of Cardiology Foundation.

D issection and re-entry techniques (DARTs)

during percutaneous coronary intervention
(PCI) are key to achieving safe and effective
recanalization of chronic total occlusions (CTOs).1,2
with vessel exit and perforation, especially when the
exit points are subsequently enlarged with a micro-
catheter. The use of knuckled wires (often referred
to as “knuckles”) is advocated to prevent perforation,
Several studies have demonstrated similar outcomes improve efficiency, and achieve safe dissection.8,9
following extraplaque stenting compared with when Several wires are now available to perform either
the plaque is stented following intraplaque wir- antegrade or retrograde dissections, and their use
ing.1,3-7 The use of stiffer wires, especially when the increases the chance of remaining within the vessel
course of the vessel is ambiguous, may be associated architecture. Although dissections may be performed

From the aGeorgia Heart Institute, Northeast Georgia Health System, Gainesville, Georgia, USA; bHeart, Vascular, and Thoracic
Institute, Cleveland Clinic Foundation, Cleveland, Ohio, USA; cDivision of Cardiology and Angiology II, University Heart Center
Freiburg – Bad Krozingen, Bad Krozingen, Germany; dDivision of Internal Medicine and Cardiology, Heart Center Lahr, Lahr,
Germany; eHenry Ford Hospital, Detroit, Michigan, USA; fDivision of Cardiology, Department of Medicine, University of Wash-
ington, Seattle, Washington, USA; gLondon Health Sciences Centre, Division of Cardiology, Department of Medicine, Western
University, London, Ontario, Canada; hHeart Health Institute, Scarborough, Ontario, Canada; iUniversity of Toronto, Toronto,
Ontario, Canada; jThe Christ Hospital Heart and Vascular Institute, Cincinnati, Ohio, USA; kHôpital Valenciennes, Valenciennes,
France; lNewYork-Presbyterian Hospital, Columbia University, New York, New York, USA; m
Saint Luke’s Mid America Heart
Institute, Kansas City, Missouri, USA; and the nMinneapolis Heart Institute, Minneapolis, Minnesota, USA.
The authors attest they are in compliance with human studies committees and animal welfare regulations of the authors’
institutions and Food and Drug Administration guidelines, including patient consent where appropriate. For more information,
visit the Author Center.

Manuscript received June 21, 2024; revised manuscript received August 8, 2024, accepted September 3, 2024.

ISSN 1936-8798/$36.00 https://doi.org/10.1016/j.jcin.2024.09.066

2412 Rinfret et al JACC: CARDIOVASCULAR INTERVENTIONS VOL. 17, NO. 20, 2024

The Art of Knuckle Wire OCTOBER 28, 2024:2411–2424

ABBREVIATIONS within the plaque of the occlusion, it is

AND ACRONYMS HIGHLIGHTS
believed that most knuckled wires travel in
the medial layer of the vessel. 10
The type of  DARTs are advocated for long and calci-
BASE = balloon-assisted
subintimal entry
knuckle, the way it is formed, its size or fied CTO segments to avoid perforation.
width, and its behavior are among concepts
CART = controlled antegrade  We describe 2 fundamental knuckle be-
and retrograde re-entry that need accurate description to enhance
haviors, the rolling and traveling
technique communication and effectively teach these
knuckles, and their use.
CTO = chronic total occlusion techniques. Although antegrade and
DART = dissection and re-entry retrograde DARTs have been extensively  Better description of knuckle behavior
technique described in textbooks 11-13 and peer-reviewed should enhance communication and
PCI = percutaneous coronary papers, the details of safe dissection tech- knowledge transfer.
intervention
niques remain counterintuitive to many op-
STAR = subintimal tracking
erators. We introduce new concepts of microcatheter exchanges and subsequent maneuvers
and re-entry
knuckle dissections and present expert with its balloon-trapping capacity. In antegrade
consensus on best practices for performing coronary dissection and re-entry, the use of a TrapLiner helps
dissections during CTO PCI. plug the dissection plane to prevent hematoma for-
mation. Newer guide extensions, such as LiquID
GETTING READY TO CREATE (Seigla Medical), have a larger internal diameter,
DISSECTION PLANES allowing the easier use of trapping balloons inside the
guide extension, and can be an alternative to the
First, operators should understand that dissection TrapLiner. Although antegrade dissection can be
methods will have important consequences on sub- performed through a 6-F guide with a TrapLiner,
sequent re-entry techniques. DARTs may be appro- some techniques such as power knuckle (explained
priate only in cases in which large branches are not later) may not be possible without removing the
expected to be excluded with subsequent ballooning guide extension. As such, we recommend at least a
and stenting. Antegrade dissection can be performed 7-F antegrade guide.
after unintentional or intentional wiring of a plane Resistance feedback from a nonknuckled wire
within the vessel architecture, in either the intra- provides confidence that it is in the vessel architec-
plaque or the extraplaque space, but the wire does ture, especially if the wire “dances” with vessel
not track into the distal true lumen. 1,2 Intentional structures such as calcium or other wires already in
dissection techniques require appropriate guide sup- place. Starting the knuckle in this position will usu-
port and the use of a microcatheter, usually in its ally be the next step. The best wires to start a
shortest version available (130 or 135 cm). There are dissection plane are discussed in the next section.
several microcatheters on the market, with different Knuckles are a more efficient way to cross long le-
entry profiles (simple tip taper, polymeric nose cone, sions and should be started early when the lesion
metallic screwlike pattern, fully metallic, etc), and it length is >20 mm, especially when the course of the
is often from trial and error that an operator may coronary is ambiguous. 8 However, if the cap of the
choose to switch from one microcatheter to another. CTO is also ambiguous, defined as an uncertain
We discourage the default use of lower profile location at the presumed end of the visible coronary
microcatheters that are usually dedicated for the lumen, there are several already described strategies
retrograde approach, as their thinner construction to create a dissection plane safely, often referred to as
makes them more vulnerable to damage and less “move-the-cap techniques.” 10,14,15 One of these
supportive. Also, dilating the dissection track with a techniques is scratch and go. This involves the
larger microcatheter will be useful prior to delivering intentional puncture of a plaque or the wall proximal
a dedicated re-entry device. Using a guide extension, to the presumed proximal cap with a high-gram
especially the TrapLiner (Teleflex), can ease the nonjacketed tapered wire, typically bent with a 45 
initiation of the dissection and exchange of catheters. angle at least 2 to 3 mm from the tip for better reach.
Although other guide extensions may provide similar If the stiffer wire provides feedback of resistance and
support, the TrapLiner also offers the possibility to the tip dances with the coronary architecture, the
trap the microcatheter with its balloon inflated when microcatheter is advanced a few millimeters into the
forming the knuckle, augmenting the support and plane, and the stiff wire is exchanged for polymer-
reducing the risk that the microcatheter will back up jacketed wire. A short attempt to feel the same
from its position. Moreover, the TrapLiner facilitates resistance is warranted to confirm that the
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OCTOBER 28, 2024:2411–2424 The Art of Knuckle Wire

microcatheter is in the vessel structure. The balloon- without antegrade contrast injection with the idea
assisted subintimal entry (BASE) technique (and its that the more tissue (greater the distance) between
derivates) is another maneuver to manage an ambig- the new dissection plane and the perforation, the
uous proximal cap and may be safer than scratch and more likely sealing will occur. When a microcatheter
go when possible. It involves a workhorse wire in the has been advanced through the adventitia, the like-
true lumen of the proximal nonoccluded portion of lihood of a clinically relevant perforation becomes
the vessel (delivered at the cap or in a branch arising much higher. Evidence of contrast extravasation
proximal to the cap), a semicompliant or when pulling the microcatheter a few millimeters
noncompliant balloon sized to the vessel caliber back will confirm the operator’s doubts. Complete
delivered on the workhorse guidewire, and a micro- removal of the microcatheter will result in more
catheter tip placed either proximal to the balloon or bleeding, and antegrade contrast injections will
under the balloon body. Inflations are performed, enlarge the leak and facilitate the creation of a track
ideally on an intimal plaque, to create dissection from the vessel to the pericardial space; maintaining
planes. Following this, a polymer-jacketed wire, with the microcatheter position until proper management
a longer bend (2-3 mm) or a double bend, is advanced of the hole in the artery is key. If a retrograde
in the dissection plane. Subintimal tracking is approach is feasible, it should be considered
confirmed by the wire spiraling around the true promptly, as retrograde dissections and tracking are a
lumen wire with the balloon in place, while “dancing” highly effective way to seal a perforation. Therefore,
is phase with the other gear in place. Several varia- operators should be facile with all hybrid CTO PCI
tions of this technique have been described. When approaches to use these intentional dissection tech-
the balloon is advanced partially into a side branch niques. Only when additional dissections have pro-
and kept inflated when attempting to track the main gressed favorably should the operator consider
branch wall and create the knuckle, it is referred to as removing the microcatheter (while leaving a wire into
side-BASE.16 This technique is aimed at preventing the space for better subsequent access) and assess for
the wire from entering an occluded or patent sec- a perforation with a gentle contrast injection. If
ondary side branch instead of the body of the CTO. perforation is greater than Ellis grade 1, the micro-
“Power knuckle” involves using a balloon to “pin” the catheter should be readvanced to “plug the hole,” and
microcatheter while pushing the wire, already in proper management of the perforation should be
the extraplaque, to increase support for folding the done promptly, including coiling of the track, pro-
wire and creating the knuckle. Finally, BASE–power longed balloon inflation, creating additional dissec-
knuckle is a more aggressive but very effective tech- tion planes to exclude the exit point, different
nique following the BASE technique.10 It involves retrograde tracking of the occlusion when possible,
inflating the balloon to pin the tip of the micro- and aborting the procedure and reversing
catheter under the balloon, or leaving the micro- anticoagulation.
catheter tip proximal to the inflated balloon, and An alternative and safer technique is to avoid
pushing a polymer-jacketed wire to create the advancing the microcatheter over a higher gram
knuckle while the balloon is kept inflated, hoping that wire that was used to puncture the extraplaque
the displacement of the microcatheter toward the space and exchange the higher gram wire for a
vessel wall or the obstruction of the true lumen with polymer-jacketed wire with a similar CTO bend
the balloon, along with dissections from previous steered to track the same channel created by the
balloon inflations, will force the knuckle to track the stiffer tip wire. The behavior of the polymer-
wall, not the lumen. Operators should be ready to jacketed wire will confirm or refute tracking of a
alternate back and forth between move-the-cap safe extraplaque space. In case of wire exit beyond
techniques to initiate the dissection safely. the adventitial border, the situation will be much
If any wire behaves strangely and seems to easier to manage, as the track will only be limited
advance freely outside the presumed borders of the to a guidewire size, as opposed to a microcatheter
vessel, it has likely exited the vessel structure. At this enlarged one. Guidewire exits from the body of the
point, it is key not to advance the microcatheter, as CTO are usually benign events, as the hole created
this will expand the hole; creating a different is small, and plaque recoil will likely close it after
dissection plane can exclude the exit point most of the removal of the wire. However, guidewire exits
the time. If the microcatheter has already been proximal to the CTO body resulting from move-the-
advanced into that space, the operator should leave cap techniques may need to be managed as
the microcatheter in place, use a second micro- described earlier, as these exits are exposed to
catheter, and start a different dissection plane coronary perfusion pressure.
2414 Rinfret et al JACC: CARDIOVASCULAR INTERVENTIONS VOL. 17, NO. 20, 2024

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T A B L E 1 Polymer-Jacketed Wires Knuckling Properties

Tapered Soft Polymeric Nontapered Stiffer Polymeric Dedicated Wire for Knuckling

Most used Fielder XT (Asahi Intecc) Pilot 200 (Abbott) Gladius Mongo/MG (Asahi Intecc)
Alternatives Fighter (Boston Scientific), Bandit Gladius EX (Asahi Intecc), Raider None
(Teleflex) (Teleflex)
Rolling knuckle Excellent Very good, but more difficult to fold at the Good but will damage the wire and will
properties beginning; great for larger knuckles likely not be usable for traveling
Traveling knuckle Good, especially if in a smaller vessel; Not recommended, as its core is bigger, Excellent, primary role
properties tip of wire needs to detach from and the fold width will be larger
the proximal area of the plaque

Operators should exercise extreme caution when the risk for wire fracture, and some operators will
tracking a microcatheter on a high-gram tapered-tip prefer the Pilot 200 or the Raider in this family. The
wire believed to be in the subintimal space. Although Raider also has a distal radiopaque segment extend-
very experienced operators can more confidently ing to 10 cm, improving visualization of the dissecting
assess if a penetrative wire is not outside the vessel edge of the knuckle compared with the Pilot 200,
structure, less experienced operators should avoid which has a 3-cm distal radiopaque segment.
tracking a hard wire with a microcatheter in the
NONTAPERED (0.014-INCH) MEDIUM-TIP-LOAD
extraplaque space.
(3 G) DEDICATED KNUCKLING WIRE OR THE “DEDI-
CATED KNUCKLE WIRE”. The Gladius Mongo (or MG
TOOLS TO CREATE AND MANAGE
outside the United States; Asahi Intecc) has a com-
DISSECTION PLANES
posite core structure that creates a weaker point 6 to
7 mm proximal to the tip aimed at directing longitu-
Once the guidewire and microcatheter are confidently
dinal forces applied on the wire to turn into folding
placed into the vessel architecture, the operator is
forces at this level when the tip encounters resis-
ready to initiate the dissection. There are 3 families of
tance. The wire tip then folds on itself, creating
polymer-jacketed guidewires currently used for
a tight knuckle, which can be pushed against
knuckles (Table 1)—soft tapered polymeric wires,
resistance.
nontapered polymeric wires, and the dedicated
knuckle wire—and 1 dedicated device, the CrossBoss DEDICATED DISSECTION DEVICE (CrossBoss).
(Boston Scientific). In this section we focus on their Although popular at the introduction of antegrade
major properties, when to use them, and their dissection and re-entry techniques, the CrossBoss has
limitations. fallen out of favor with the advent of high-
performance microcatheters and the Gladius Mongo
TAPERED-TIP (0.009- OR 0.008-INCH) LOW-TIP-LOAD
(MG) wire. The device is a stiff braided metallic
(<1 G) FAMILY OR “SOFT TAPERED POLYMERIC”. This
catheter with a 1-mm blunt ball at the tip, tracking a
family includes the Fielder XT (with a 0.009-inch
0.014-inch guidewire. Once into the occlusion, the
tapered tip) and related wires with composite cores,
wire is retracted and the catheter spun fast without
the Fielder XT-A and XT-R (Asahi Intecc), the Bandit
the wire to extend a dissection plane in a less trau-
(with a 0.008-inch tapered tip) (Teleflex), and the
matic fashion. Because of its stiffness, the CrossBoss
Fighter (0.009-inch tip) (Boston Scientific). As com-
has a predilection for tracking branches arising from
posite cores can theoretically increase the risk for
the outer border of the vessel, especially in the right
wire fracture, with increased metallic components at
coronary artery. It was quickly identified as a “poor
bent wire points, we recommend the classic Fielder
starter” but remains an alternative to minimize the
XT, the Bandit, or the Fighter. For inventory pur-
size of the subintimal space and hematoma in the
poses, getting used to one of these guidewires for
distal segment of the dissection (often referred as
knuckling is enough.
“dry dissection”) prior to the introduction of a dedi-
NONTAPERED (0.014-INCH) MEDIUM-TIP-LOAD (3 TO 4 G) cated re-entry device.
FAMILY OR “STIFFER NONTAPERED POLYMERIC”. This
family includes the classic Pilot 200 (Abbott FUNDAMENTAL KNUCKLE BEHAVIORS
Vascular), the Gladius EX (Asahi Intecc), and the
Raider (Teleflex). More complex composite cores, Following an understanding of how to get appro-
such as those found in the Gladius EX, may increase priate support to enter a dissection plane and the
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OCTOBER 28, 2024:2411–2424 The Art of Knuckle Wire

F I G U R E 1 Rolling Knuckle (the “Catch, Coil, and Roll” Maneuver)

(A) Microcatheter at proximal cap. (B) Guidewire catching tissue. (C) Guidewire tip collapsing like a coil. (D) Guidewire pushed, rolling from its
entrapped tip and elongating. (E) Dissection forces from the rolling edge of the knuckle. (F) Larger wire core reaching the edge of dissection.

wires that are needed for the task, the operator will the vessel structure,” given its low gram and tapered
need to learn how knuckled wires from the afore- tip design. The operator pushes the wire to collapse
mentioned families behave and when to use them. the few distal millimeters segment of the wire into a
We divide knuckles into 2 types: the rolling knuckle tight bend into the wall, as one would want to do with
(Figures 1 and 2) and the traveling knuckle (Figures 3 a small coil. The sequence of forming the rolling
and 4). Understanding their behavior and when to knuckle is as follows. First, the wire is shaped with a
use them will increase an operator’s confidence in small distal J, or simply used straight in the case of a
using the extraplaque space (Central Illustration). Fielder XT. Second, it is drilled to engage a space,
hoping to see or feel the wire meet resistance and see
THE ROLLING KNUCKLE. Although it can be done the wire catching tissue, subsequently starting to
with nontapered polymeric guidewire, this action is collapse on itself in the manner of a small coil. This
typical of the tapered soft polymeric wires. The behavior indicates that the wire is confined to the
Fielder XT (or its equivalent) is the best wire to “feel coronary architecture, either within the plaque or
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F I G U R E 2 Rolling Knuckle Example

(A) Left circumflex coronary artery chronic total occlusion (CTO) with numerous bridging collateral vessels. (B) Tip injection at the proximal cap showing the bridging
collateral vessels and an ambiguous cap. (C) Scratch and go with a stiff guidewire, aiming at the plaque. (D) Fielder XT pushed into the wall, collapsing like a coil. (E)
Wire removed and “Carlino technique” performed to soften the tissues. (F) Fielder XT pushed again, catches the tissues and starts rolling into the CTO body. (G) The
rolling edge of the knuckled wire dissects the extraplaque space (white arrow), as the tip of the wire is trapped proximal in the plaque (black arrow). (H) Angiography
showing the front edge of the knuckled wire next to the true lumen distally (white arrow) while the tip of the wire is still into the proximal cap (black arrow).

within the extraplaque space. If the wire seems to forward, the dissection force will be created by a
extend beyond the borders, not tracking calcium or progressive increase in the internal core size of the
the presumed trajectory of the vessel, or forming an wire. Moving forward, the leading dissection edge
unusually large knuckle, it has likely exited the vessel will be created by a more proximal and stiffer body of
structure. If the microcatheter has not followed into the wire, opening the knuckle width or loop into a
that position, the microcatheter should be pulled larger one. When the fold width seems to have
back a few millimeters and a different dissection reached the presumed size of the vessel at its front
plane initiated with the techniques explained earlier. edge or even a larger size, it is likely because it was
Simple redirection of the dissection planes with a elongated or rolled enough. Subsequently, the tech-
nontapered polymeric wire (see wire redirection nique will involve advancing the microcatheter,
later) could be done. Third, if the wire tip collapses pulling the wire back into the microcatheter, and
like a coil, it is likely in a good position. Rolling the starting again the knuckle like a “coil” and, once the
knuckle is the step typically following the “coiling” or tip is trapped, rolling again to elongate the wire,
catching part. As the tip of the wire is entrapped into creating dissection forces, often referred as knuckle
the tissues, pushing the wire will create a bend, size management (Figure 5). Retracting the wire
forming a knuckle. The distal wire tip will remain completely sometimes results in the microcatheter tip
fixed or anchored in tissue while the more proximal forming a J when the dissection space is large.
knuckled body of the wire will “roll” forward into the Although it can be disconcerting with less experience,
dissection plane as it is elongated longitudinally, the tip will invariably straighten when readvancing
forming the knuckle structure. The dissection force the wire. Once the wire is rolling, it should be pushed
will start with the distal softer radiopaque part of the without spinning or steering the wire to avoid
wire, but as the wire is pushed to roll and elongate creating a knot or breaking the wire, especially when
JACC: CARDIOVASCULAR INTERVENTIONS VOL. 17, NO. 20, 2024 Rinfret et al 2417
OCTOBER 28, 2024:2411–2424 The Art of Knuckle Wire

F I G U R E 3 Traveling Knuckle (the “Catch, Fold, and Travel” Maneuver)

(A) Gladius Mongo tip catching tissue. (B) Longitudinal forces applied to wire. (C,D) Guidewire tip folding at the dedicated bending point. (E) Wire folded. (F) Dissection
forces from the front edge of the knuckle. (G-J) Whole knuckle and wire traveling forward.

performed in the retrograde direction. In summary, into a space created by a soft tapered polymeric one is
the sequence required for executing a rolling knuckle usually easy, with the wire bent at 45 , or even with
can be remembered as “catch, coil, and roll.” only a 1- to 2-mm bend from the tip. As the wire
The best knuckle wire family for this type of “catches” tissue and the tip starts collapsing, pushing
dissection technique is the soft tapered polymeric, as the wire will create a more “powerful” knuckle
the “coiling part” of its delivery is easier to achieve compared with the softer one, as the leading edge of
compared with a stiffer nontapered polymer-jacketed the dissection will be created from a larger wire core
guidewire such as the Pilot 200 or Raider. As its core size. Knuckles may also need redirection using the
is smaller distal, the fold that creates the dissection techniques explained later. Rolling knuckles are the
force on a soft polymeric tapered guidewire will be best starters but poor finishers of dissection planes, as
tighter, creating a “smaller knuckle.” However, they cause larger dissection planes that may impair
smaller knuckles (with soft tapered polymer-jacketed subsequent attempts at re-entry, especially in the
or dedicated knuckle wire) are more likely to track antegrade direction. Switching for a “traveling
occluded branches within the CTO body or more knuckle” is warranted, as described in the next
distally (Figure 6). Exchanging for a nontapered section.
stiffer polymeric wire will create a larger fold that will
not enter smaller side branches and stay in the main THE TRAVELING KNUCKLE. This behavior is typical
vessel. Folding a nontapered stiffer polymeric wire of the Gladius Mongo (MG) and sometimes of the
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F I G U R E 4 Traveling Knuckle Example

(A) Right coronary artery contrast-induced iatrogenic dissection due to malalignment of a guide catheter through a transcatheter aortic valve replacement. (B) Gladius
Mongo (MG) pushed to fold on itself. (C) Microcatheter advanced and guidewire pushed to travel into the dissection plane. (D) Guidewire encounters resistance.
(E) Guidewire pushed harder, which opens the fold width on the resistant area. (F) Knuckle collapses and becomes smaller in size. (G,H) Wire travels forward freely,
indicating successful re-entry.

Fielder XT, especially when the rolling maneuvers beyond the distal CTO cap to prepare for device-based
result into spontaneous re-entry (at a branch or if the re-entry, as it creates a relatively limited space in
knuckle moved to a more superficial dissection which the device, usually a Stingray balloon (Boston
plane), often referred as subintimal tracking and re- Scientific), is likely to have good contact with the
entry (STAR). 11 A traveling knuckle behaves very vessel wall. The Mongo (MG) is also the choice wire to
differently than a rolling knuckle. Unlike with a roll- perform STAR, especially when pushed against the
ing knuckle, the tip of the wire on a traveling knuckle carina of big branches such as in a distal right coro-
is not fixed in the plaque. Once the tip is folded, the nary artery. The knuckle may also navigate intra-
whole wire moves forward, with the fold remaining at plaque or superficially and re-enter into the vessel at
the same place on the wire. It can be remembered a weaker intimal segment, which is unfortunately
as the “catch, fold, and travel” knuckle maneuver. unpredictable. It can also behave the same way
For the Gladius Mongo (MG), the fold will remain 6 to retrogradely and re-enter as a “retrograde STAR.” It is
7 mm proximal to the tip, and the whole knuckled tip important to mention few nuances in behavior when
is therefore moved forward. The dissection force will using the Mongo (MG) to create dissections in the
be at the wire bend that moves into planes, dissecting proximal segment of a coronary: 1) initial folding of
them. The fold width should remain narrow during the Mongo (MG) is sometimes difficult, with a fold 6
these maneuvers (Figure 4). An unexpected enlarge- to 7 mm proximal to the tip, especially in smaller
ment of the fold width indicates a resistance to the vessels; 2) an attempt to fold the wire may result in
progression of the wire but can sometimes mean exiting straight outside the vessel structure; 3) once
vessel exit and warrants appropriate corrections, the knuckle is formed, longer travel with the Mongo
such as creating an alternative track and avoiding (MG) increases the chance to track side branches, as
advancing the microcatheter. The Mongo (MG) is the knuckle is small enough to collapse and take a
currently the choice wire to finish a dissection plane narrower route, increasing the risk for distal wire
JACC: CARDIOVASCULAR INTERVENTIONS VOL. 17, NO. 20, 2024 Rinfret et al 2419
OCTOBER 28, 2024:2411–2424 The Art of Knuckle Wire

C ENTR AL I LL U STRA T I O N Two Principal Knuckle Wire Behaviors When Using Dissection in
Chronic Total Occlusion Percutaneous Coronary Intervention

Rinfret S, et al. JACC Cardiovasc Interv. 2024;17(20):2411–2424.

perforation; and 4) if used as a rolling knuckle, its the knuckle abruptly collapses in size and leaps for-
design of longitudinal forces delivered on a tight ward in transitioning from the subintimal to luminal
distal knuckle is defeated. As such, the Mongo (MG) position. These characteristics make soft tapered
carries some of the disadvantages of the CrossBoss polymeric wires the preferred wires for initiating the
but offers many other advantages. Although it may STAR technique.
not be the best starter, especially in a proximal In contrast, traveling knuckles can turn into rolling
segment of a coronary, it is invariably the best wire to knuckles as well. Although the Gladius Mongo (MG)
progress into the vessel architecture and to finish a can travel long distances, it will sometimes meet
dissection maneuver, once the extraplaque space is resistance that will turn the knuckle into a rolling
well controlled. one. At this point, the wire will behave exactly like a
Rolling soft polymer-jacketed wires can convert stiffer nontapered polymeric wire, and its subsequent
into traveling knuckles if true-lumen re-entry is ability to travel as originally designed will be lost.
achieved. Separation of the distal wire tip from the
vessel wall followed by a longitudinal displacement NUANCES BETWEEN ANTEGRADE AND
of the folded wire toward the distal true lumen, RETROGRADE KNUCKLES
decrease in the knuckle width, and loss of resistance
indicate true-lumen re-entry. On fluoroscopy, these Although knuckle behavior is similar when pushed
rapid changes are manifest as a “shrink and pop” as in the retrograde vs antegrade direction, a few
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F I G U R E 5 Knuckle Size Management

(A) Knuckle has enlarged because of the larger core of the wire reaching the folded section (elongated to its maximum). (B) Microcatheter
advanced. (C,D) Guidewire pulled back. (E,F) Guidewire pushed again to roll forward.

differences must be highlighted. Retrograde track graft anastomosis remnants; to overcome this,
knuckles, especially rolling ones, rarely track the use of a larger, stiffer, polymeric wire rolling
branches, as their origins are directed in the opposite knuckle can be very effective, especially antegrade,
direction, except for branches arising close to 90 to track the main vessel instead of the graft remnant.
from the main vessel or for graft remnants. As such, a Also, when possible, delivering a balloon distally
traveling Mongo (MG) knuckle is less likely to track through the occluded graft can block the entrance of
branches retrogradely and can be pushed on a longer the graft, in a manner like the side-BASE technique,
distance, with the advantage that it can sometimes and help track the vessel proximal to the distal
re-enter spontaneously into the proximal true lumen anastomosis of the graft.
(retrograde STAR), something that seldom happens Although antegrade knuckles should usually be
with retrograde rolling knuckles. The use of the Car- kept small close to an antegrade re-entry site, it is
lino technique can be helpful retrograde, especially different when performing the controlled antegrade
when knuckles fail to progress. 17 The Carlino tech- and retrograde re-entry technique (CART) and reverse
nique may also be useful antegrade in the case of CART. Retrograde knuckles with a larger width, rolled
stalled knuckles. In post–coronary artery bypass and elongated up to the proximal cap, will facilitate
grafting patients, rolling or traveling knuckles can puncture toward the extraplaque space from the
JACC: CARDIOVASCULAR INTERVENTIONS VOL. 17, NO. 20, 2024 Rinfret et al 2421
OCTOBER 28, 2024:2411–2424 The Art of Knuckle Wire

F I G U R E 6 Side-Branch Management

(A) Gladius Mongo (MG) traveling. (B) Width of the knuckle is smaller than a branch. (C) Wire tracks the branch and gets off track with the main vessel. (D) Wire behavior
recognized and wire pulled back. Option 1: (E1) Wire with larger core pushed on resistance. (F1) Wire folds. (G1,H1) Knuckle is larger than the branch and therefore
tracks the main vessel. Option 2: (E2) Wire steered to track away from branch and aiming at resistance. (F2) Microcatheter advanced. (G2) Gladius Mongo (MG) knuckled.
(H2) Knuckled wire travels in a different plane.

antegrade side. Similarly, a retrograde puncture remains in the vessel structure. Indications of a po-
attempt toward a larger antegrade knuckle will be tential exit of the knuckle include an enlarged
easier. knuckle disproportional to the size of the vessel or a
wire not “dancing” with the distal true lumen or the
ADJUNCTIVE MANEUVERS FOR calcium, contrast extravasation, and visualization of
MORE EFFECTIVE AND SAFER an increasing distance from the wire and coronary
DISSECTION PROCEDURES structures such as calcifications, contrast stains, old
stents, or surgical clips. Frequent changes of the
THE “JACKHAMMER” MANEUVER. Starting a knuckle C-arm position in orthogonal views or the use of
is a counterintuitive maneuver for most operators. biplane views, when possible, will help ensure that
Although finesse and delicate push and rotation of the wire is tracking appropriately. If the knuckle does
wires are warranted when traversing a plaque in a not increase in size but fails to track the distal vessel,
patent true lumen or a collateral channel, more the knuckle has deviated toward a side branch, and
abrupt forces need to be applied on a wire to create a caution should be exerted to stop the dissection at
dissection, especially after it has started to behave as this point and redirect the knuckle as explained later.
a coil, to form the knuckle edge. It is often through
AVOIDING CONTRAST AND SALINE INJECTION.
jerky movements, in the fashion of a jackhammer,
Operators should never inject contrast or saline via
with repetitive longitudinal tapping forces applied on
the antegrade guide, as a controlled dissection can
the wire that the knuckle will form and progress.
turn into an uncontrolled one by hydraulic pressuri-
USE OF ORTHOGONAL VIEWS. When performing zation. Removing the antegrade syringe from
dissection in a CTO vessel, it is key to ensure that the the manifold is a simple tip to avoid inadvertent
wire components’ (tip, body, and fold) position antegrade injection and uncontrolled hydraulic
2422 Rinfret et al JACC: CARDIOVASCULAR INTERVENTIONS VOL. 17, NO. 20, 2024

The Art of Knuckle Wire OCTOBER 28, 2024:2411–2424

dissection. If operators are using automatic injectors, beyond the resistant point then be “de-escalated’ to
they should be used only on the retrograde catheter. polymer-jacketed wires to confirm their presence in
Also, blood for activated clotting time should be the vessel architecture with a proper “dance.”
aspirated from the retrograde guide, as a flush of the Rotating a knuckled wire should never be per-
catheter after blood withdrawal can extend formed retrogradely, as it can turn the wire tip into a
a dissection. knot, preventing retrieval of the guidewire into the
microcatheter and forcing the operator to pull the
AVOIDING “EXPLODING” KNUCKLE. An exploding
wire and retrograde microcatheter altogether and to
knuckle is one that starts in a compacted form but
start over. Although pulling all the retrograde gear
quickly becomes larger, often larger than the pre-
from a graft or a septal connection is usually benign,
sumed size of the vessel being dissected. Recognizing
it could have disastrous consequences through an
the behavior early is key, as it indicates an exit from
epicardial collateral. In contrast, steering a knuckle
the vessel architecture. With a traveling Gladius
antegrade is something that can be tried, especially to
Mongo (MG) knuckle, an exit will be evidenced by an
redirect a dissection plane; knotting the wire will be
awkward and unpredicted unfolding of the distal part
less consequential, as the antegrade gear can usually
of the knuckle, indicating that the wire is not con-
be pulled safely. Operators should be able to track the
tained anymore into a confined space. Although it
same antegrade planes already created with new
may rarely indicate re-entry when dissecting a very
wires.
large vessel, a retrograde injection will allow the
operator to confirm re-entry or a more likely wire exit. CARLINO TECHNIQUE. A small tip injection of
If a wire exit is suspected or confirmed, the micro- contrast from a microcatheter can help change tissue
catheter should be pulled back a bit and knuckling compliance and delineate the vessel structure. It is
reattempted with a soft tapered polymeric wire, especially useful after successful “coiling” with a soft
starting like a coil, and followed with a rolling tech- polymeric tapered guidewire that cannot progress
nique. Once resistance is felt, the wire is then pushed toward elongation or rolling (Figure 2). After the
and elongated. If the wire keeps repeating the same collapsing of a wire confirms the proper position in
behavior, a nontapered and stiffer polymeric wire can the vessel structure, the wire is removed, and injec-
be used if the vessel is presumed to be larger than tion of 0.5 to 1 mL of contrast in the area will help
3 mm. Otherwise, a wire redirection technique should confirm the position and initiate the dissection. 18
be considered (Figure 6). Taking the wire back or using a stiffer nontapered
one may subsequently succeed.
KNUCKLE REDIRECTION. If the knuckle is believed
to enter branches or go off track, or following the
ASPIRATION FROM THE TIP OF THE MICROCATHETER.
occurrence of an exploding knuckle, a knuckle redi-
Although this technique is often essential to mitigate
rection must be performed. The ambiguity of the
the expansion of a hematoma in the dissection planes
course of the vessel at this point will guide wire se-
prior to re-entry, it may also be helpful during
lection. When ambiguous, we prefer the use of a
dissection techniques, especially when the knuckle
stiffer nontapered jacketed wire, with a small CTO
wire seems to “float” into a coronary segment,
bend, drilled and directed toward a different segment
without progression. Reduction of the hematoma
of the vessel, like toward a clear calcified segment. If
space could provide less opportunity for the micro-
feeling resistance, the microcatheter is advanced, and
catheter to deflect backward, increasing the chance
the wire knuckled with a coil and rolling technique.
that the knuckle can continue moving forward. It will
Alternatively, a traveling knuckle technique with a
also improve the visualization of the distal vessel
Mongo (MG) can be subsequently performed
target with contralateral contrast injection, to ease
(Figure 6).
subsequent re-entry maneuvers.
Some operators will occasionally use a midgram or
stiffer wire to redirect a dissection track. The Gaia BALLOON ANCHORING. Balloon anchoring can be
Next 2 or 3 (Asahi Intecc), or the Judo 3 or 6 (Boston done in several ways. If support is lacking, an
Scientific) with their high steerability and intermedi- anchoring balloon can be inserted into a side branch
ate tip load can be effective, as they also provide good to increase support for the knuckle push or the
distal tip feedback, confirming that the wire remains microcatheter advancement. If a TrapLiner is used,
in the vessel structure prior to advancing the micro- inflating the balloon will trap the microcatheter in
catheter. Again, these wires should be used judi- place to facilitate the rolling of a knuckle. Otherwise,
ciously and allowed to advance only 2 to 3 mm a balloon can also be inserted into the proximal
JACC: CARDIOVASCULAR INTERVENTIONS VOL. 17, NO. 20, 2024 Rinfret et al 2423
OCTOBER 28, 2024:2411–2424 The Art of Knuckle Wire

patent part of the vessel (or in the distal tip of the confirm intra- or extraplaque location of the wire.
guide) to pin the microcatheter for the same purposes Although a large rolling knuckle will usually progress
(power knuckle). extraplaque, smaller ones and traveling knuckles can
progress intraplaque. The final dissection route can
ALTERNATING BETWEEN MICROCATHETERS. only be confirmed by intravascular ultrasound ex-
Although the same microcatheter can sometimes be amination.20 As such, bidirectional knuckles and
used from the proximal part of the vessel up to the re- dissection planes during a retrograde procedure do
entry site, poor progression despite good movement not ensure that both wires are in the same intraplaque
of the wire can indicate microcatheter “fatigue,” tip or extraplaque space. Intravascular ultrasound can
damage, or inadequate properties for the task and help identify their true location and solve difficult
should warrant a change of microcatheter. We reverse CART.21
discourage the use of thinner microcatheters, usually
dedicated for the retrograde approach, as they are CONCLUSIONS
less resistant to damage or overtorquing and do not
dilate the track as well as 3-F microcatheters. More liberal use of the extraplaque and subintimal
spaces has resulted in a higher success rate,
PLAQUE MODIFICATION DURING DISSECTION
improved efficiency, and likely reduced complica-
MANEUVERS. If microcatheters fail to progress into a
tions in complex CTO PCI cases over the past 15
dissection plane (as opposed to the plaque), the use of
years. Stenting of a subintimal space is associated
a small (#1.5 mm) balloon, especially one with an
with a similar risk for long-term major adverse
ultra-low profile, can help overcome resistant areas
cardiac events compared with intraplaque stenting,
after dilatation. However, we do not recommend
19 supporting the use of dissection as an efficient and
balloon-assisted microdissection, as intentionally
safe strategy in CTO PCI. 1,3-9 Although knuckled
bursting a small balloon can result in the perforation
wires have been incorporated into most operators’
of the adventitial border. With a retrograde approach,
technical portfolios, the various nuances had never
the operator can also trap a retrograde wire with an
been described. By better understanding knuckled
antegrade balloon to facilitate the progression of a
wire behavior and methods to achieve safe and
retrograde microcatheter. In the same fashion but
effective dissection planes, operators will gain a
only when feasible (large septal collateral or saphe-
deeper understanding of retrograde or antegrade
nous vein graft as a retrograde conduit), an antegrade
dissection technique nuances, which are paramount
wire can be trapped with a balloon delivered retro-
to achieving higher success while keeping the risk
grade. Creating an alternative dissection track is
for complications as low as possible.
sometimes the only solution that will result in prog-
ress of the microcatheter. Finally, the use of a small
rotational atherectomy burr (1.25 or 1.5 mm) to modify
FUNDING SUPPORT AND AUTHOR DISCLOSURES
the resistant area, especially if calcium is present, can
Dr Rinfret has received consulting, speaker, and proctoring honoraria
be performed by experienced operators. Of note, it is from Abiomed, Boston Scientific, Medtronic, and Teleflex. Dr Khatri
sometimes necessary to cut a few cm of the tip of the has received consulting, speaker, and proctoring honoraria from
Rotawire (Boston Scientific) to allow the burr to reach Abbott, Medtronic, Terumo, Boston Scientific, and Shockwave Medi-
cal. Dr Mashayekhi has received consulting, speaker, and proctoring
the area of resistance. Following this, the operator
honoraria from Abbott Vascular, Abiomed, Asahi Intecc, AstraZeneca,
will advance a microcatheter on the Rotawire, remove Biotronik, Boston Scientific, Cardinal Health, Daiichi-Sankyo, Med-
the Rotawire, and resume the dissection techniques, tronic, OrbusNeich, Shockwave Medical, Teleflex, and Terumo. Dr

expecting some progression at the site where they Alaswad has received consulting, speaker, and proctoring honoraria
from Boston Scientific and Teleflex. Dr Azzalini has received consul-
were stalled. Because of differential cutting or
ting fees from Teleflex, Abiomed, GE Healthcare, Abbott Vascular,
ablating properties, the Rotablator (Boston Scientific) Reflow Medical, and Cardiovascular Systems; serves on the advisory
burr is expected to shave the calcium while avoiding boards of Abiomed and GE Healthcare; and owns equity in Reflow
Medical. Dr Vijayaraghavan has received consulting and proctoring
trauma to the adventitial border. However, such
fees from Acist, Abbott, Asahi Intecc, Medtronic, and Biotronik. Dr
principles have their limit, and aggressive use or
Frizzell has received consulting and speaker honoraria from Asahi
bigger burrs can result in dramatic perforation and Intecc, Boston Scientific, Medtronic, Reflow Medical, and Shockwave
should be avoided. Medical. Dr Avran has received consulting, speaker, and proctoring
honoraria from Abbott Vascular, Asahi Intecc, Biotronik, Boston Sci-
INTRAVASCULAR ULTRASOUND. Despite the several entific, Medtronic, Shockwave Medical, Teleflex, and Terumo. Dr
McEntegart has received consulting, speaker, and proctoring hono-
characteristics of the shape and behavior of the
raria from Boston Scientific and Shockwave Medical. Dr Lombardi has
knuckle (tactile and/or visual feedback), there is no received consulting fees from Asahi Intecc, Abiomed, Boston Scien-
reliable real-time fluoroscopic finding to prove or tific, Medtronic, Siemens, and Teleflex and has received royalties
2424 Rinfret et al JACC: CARDIOVASCULAR INTERVENTIONS VOL. 17, NO. 20, 2024

The Art of Knuckle Wire OCTOBER 28, 2024:2411–2424

from Asahi Intecc; his spouse is a Philips employee. Dr Grantham has shareholder in MHI Ventures, Cleerly Health, and Stallion Medical. All
received speaking fees and honoraria from Boston Scientific, Med- other authors have reported that they have no relationships relevant
tronic, and Asahi Intecc; has received advisory board fees from Tel- to the contents of this paper to disclose.
eflex and Boston Scientific; and has received institutional research
grants from Asahi Intecc, Abiomed, and Boston Scientific. Dr Brilakis
has received consulting and speaker honoraria from Abbott Vascular,
the American Heart Association (associate editor, Circulation), ADDRESS FOR CORRESPONDENCE: Dr Stéphane
Amgen, Asahi Intecc, Biotronik, Boston Scientific, the Cardiovascular Rinfret, Georgia Heart Institute/Northeast Georgia
Innovations Foundation (Board of Directors), Cardiovascular Sys-
Health System, 200 S Enota Drive NE, Suite 200,
tems, Elsevier, GE Healthcare, IMDS, Medicure, Medtronic, Siemens,
Teleflex, and Terumo; has received research support from Boston Gainesville, Georgia 30501, USA. E-mail: stephane.
Scientific and GE Healthcare; is the owner or Hippocrates; and is a rinfret@nghs.com.

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