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Natsuki Akaike, Hiroyuki Ikeda, Mai Tanimura, Minami Uezato, Masanori Kinosada, Yoshitaka Kurosaki, Masaki Chin
  1. Department of Neurosurgery, Kurashiki Central Hospital, Okayama, Japan

Correspondence Address:
Natsuki Akaike, Department of Neurosurgery, Kurashiki Central Hospital, Okayama, Japan.

DOI:10.25259/SNI_366_2025

Copyright: © 2025 Surgical Neurology International This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-Share Alike 4.0 License, which allows others to remix, transform, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.

How to cite this article: Natsuki Akaike, Hiroyuki Ikeda, Mai Tanimura, Minami Uezato, Masanori Kinosada, Yoshitaka Kurosaki, Masaki Chin. Sticking after detachment procedure of coil with floating detachment link with ball joint due to excessively bent junction: A case report and a bench-top experiment. 13-Jun-2025;16:244

How to cite this URL: Natsuki Akaike, Hiroyuki Ikeda, Mai Tanimura, Minami Uezato, Masanori Kinosada, Yoshitaka Kurosaki, Masaki Chin. Sticking after detachment procedure of coil with floating detachment link with ball joint due to excessively bent junction: A case report and a bench-top experiment. 13-Jun-2025;16:244. Available from: https://surgicalneurologyint.com/?post_type=surgicalint_articles&p=13623

Date of Submission
14-Apr-2025

Date of Acceptance
16-May-2025

Date of Web Publication
13-Jun-2025

Abstract

Background: We present a case of coil sticking, likely caused by an excessively bent junction of the coil and the delivery pusher, with a bench-top experiment to determine the cause of coil sticking in this case.

Case Description: A coil embolization procedure was performed for an internal carotid artery aneurysm. During the framing with the Axium Prime Frame coil, the tip of the microcatheter was advanced to the center of the coil mass within the aneurysm to insert the coil. After detachment, the coil became stuck. Pulling the delivery pusher allowed the coil to detach from the delivery pusher within the microcatheter. After flushing the microcatheter with heparinized saline, the proximal end of the coil fortuitously settled within the aneurysm and the procedure was concluded without complications. A bench-top experiment suggested that an excessively bent junction of the coil and the delivery pusher causes the ball joint of the floating detachment link to hook into the circular opening.

Conclusion: When using coils with a floating detachment link that has a ball joint, forcibly advancing the microcatheter while the tip of the microcatheter is aligned with the junction may cause excessive bending of the junction, resulting in coil sticking.

Keywords: Axium coil, Coil sticking, Detachment, Embolization

INTRODUCTION

Coil-related problems such as sticking, knotting, fracturing, and unraveling have been reported during coil embolization of cerebral aneurysms.[ 3 , 6 , 8 - 10 , 13 , 14 ] We present a case of coil sticking during coil embolization of a cerebral aneurysm based on intraoperative imaging findings and bench-top experiments. Since coil sticking during coil embolization is rare,[ 3 , 14 ] to the best of our knowledge, there is no detailed literature elucidating the mechanism of coil sticking due to an excessively bent junction of the coil and the delivery pusher.

CASE REPORT

History and examination

A 79-year-old woman underwent emergency coil embolization under general anesthesia for a ruptured left internal carotid-posterior communicating artery aneurysm. After systemic heparinization, a 6-Fr Fubuki dilator kit (Asahi Intecc, Seto, Japan) was inserted through the right femoral artery and placed in the left cervical internal carotid artery. Cerebral angiography revealed a left internal carotid-posterior communicating artery aneurysm (neck: 2.7 mm, dome: 3.8 × 3.9 mm, height: 4.4 mm) [ Figures 1a and b ]. As a distal access catheter, a Vecta 71 (Stryker, Kalamazoo, MI, USA) was advanced to the cavernous portion of the internal carotid artery. From there, a Transform 4 mm × 7 mm (Stryker) was guided to the neck of the aneurysm, and a Phenom 17 (preshaped to 90°, Medtronic, Minneapolis, MN, USA) was placed within the aneurysm. Framing of the neck of the aneurysm was performed with an Axium Prime Frame 3 mm × 8 cm (Medtronic) from the Phenom 17 positioned at the neck of the aneurysm [ Figure 1c ]. Toward the end of framing, the tip of the Phenom 17 was advanced to the center of the coil mass within the aneurysm, and a coil was inserted, aligning the second marker on the Phenom 17 with the alignment marker on the delivery pusher of the coil in an inverted T shape [ Figure 1d ]. In this position, the release wire connector at the proximal end of the delivery pusher was attached to the instant detacher, and the slide knob was pulled back to perform the detachment procedure. When the delivery pusher was slowly pulled back, the coil started to move. The coil was reinserted into the aneurysm and the same detachment procedure was attempted, but pulling the delivery pusher caused the coil to move again. Since detachment with the instant detacher had failed, the proximal end of the delivery pusher was bent and the release wire was pulled to forcibly to release the engagement of the delivery pusher and the proximal end of the coil. However, when the delivery pusher was pulled back, the coil started to move again. Recognizing that coil sticking had occurred, the delivery pusher was pulled within the Phenom 17 while keeping the tip of the Phenom17 positioned within the aneurysm. There was no resistance when pulling the delivery pusher and the coil followed the delivery pusher [ Figure 1e ]. After the coil followed the delivery pusher by approximately 2 cm, it detached from the delivery pusher and advanced to the aneurysm due to the recoil [ Figure 1f ]. After completely retracting the delivery pusher from the Phenom 17, flushing the Phenom 17 with heparinized saline was performed under non-fluoroscopic guidance. Fluoroscopy showed that the coil had settled within the aneurysm [ Figure 1g ]. Filling was performed with an Axium Prime Helix 3 mm × 4 cm (Medtronic) and an Axium Prime Helix 2.5 mm × 3 cm (Medtronic), and treatment was concluded with a volume embolization ratio of 27.8%, with some contrast agent still filling into the aneurysm neck [ Figure 1h ]. No rebleeding from the aneurysm was observed postoperatively, and there were no adverse events associated with the coil sticking. However, the patient’s overall condition did not improve due to worsening cerebral edema from the initial subarachnoid hemorrhage, and she died on hospital day 13.


Figure 1:

Imaging findings from coil embolization (working angle, frontal view): (a) Pretreatment cerebral angiogram. (b) Pretreatment three-dimensional cerebral angiogram. (c) The Phenom 17 is positioned at the neck of the aneurysm (white arrow) and the coil is inserted into the aneurysm. The black arrow shows the second marker on the Phenom 17. (d) The tip of the Phenom 17 is advanced to the center of the aneurysm (white arrow) and the second marker on the Phenom 17 is advanced farther (black arrow). The alignment marker on the delivery pusher and the second marker on the Phenom 17 form an inverted T-shape. (e) Pulling the delivery pusher back into the Phenom 17 causes the coil to follow the delivery pusher (black arrowhead). (f) The coil detaches from the delivery pusher and the recoil causes the coil to advance (black arrowhead). (g) After the coil detachment, flushing the Phenom 17 with heparinized saline advances the coil into the aneurysm. (h) Post-treatment cerebral angiogram showing the residual neck of the aneurysm.

 

Bench-top experiment

Medtronic provided all Axium Prime coils and microcatheters free of charge for research purposes. All experiments were performed by a single operator (NA) with 6 years of clinical experience.

When the delivery pusher of a new Axium coil was fixed to the tabletop and the slide knob of the instant detacher was pulled, the proximal end of the coil detached from the delivery pusher [ Figures 2a and b ]. After detachment, the floating detachment link was not visible at the proximal end of the coil [ Figure 2c ]. The ball joint of the floating detachment link removed from the proximal end of the coil was straight [ Figure 2d ].


Figure 2:

Bench-top experiment using Axium coil: (a) a new Axium coil fixed to the tabletop. The delivery pusher (black bidirectional arrow) and the proximal end of the coil (white bidirectional arrow) are linearly engaged at the junction (black arrow). (b) With a straight junction, the proximal end of the coil immediately detaches from the delivery pusher in a detachment process. (c) The floating detachment link is not visible at the proximal end of the coil after detachment (black arrowhead). (d) The ball joint of the floating detachment link removed from the proximal end of the coil is straight. (e) A new Axium coil fixed to the tabletop with an excessively bent junction (white arrow). (f) The delivery pusher and the proximal end of the coil remain engaged after a detachment attempt. (g) After detachment, the floating detachment link is not retracted into the coil and remains visible at the proximal end of the coil (white arrowhead). (h) The ball joint of the floating detachment link removed from the proximal end of the coil is bent.

 

When the delivery pusher of a new Axium coil was fixed to the tabletop and the junction was excessively bent [ Figure 2e ], pulling the slide knob of the instant detacher did not disengage the delivery pusher and the proximal end of the coil [ Figure 2f ]. Pulling the delivery pusher allowed the coil to detach from the delivery pusher. After detachment, the floating detachment link is not retracted into the coil and remains visible at the proximal end of the coil [ Figure 2g ]. The ball joint of the floating detachment link removed from the proximal end of the coil was bent [ Figure 2h ].

A Phenom 17 was placed within an aneurysm model made of silicone and an Axium coil was inserted through the Phenom 17. The tip of the Phenom 17 was aligned with the junction and was compressed against the aneurysm wall, resulting in an excessively bent junction [ Figures 3a and b ]. When the slide knob of the instant detacher was pulled to initiate the detachment procedure, the delivery pusher and the proximal end of the coil remained engaged [ Figure 3c ]. Pulling the delivery pusher released the engagement, and the coil detached from the delivery pusher. After detachment, the floating detachment link was not retracted into the coil and remains visible at the proximal end of the coil [ Figure 3d ]. The ball joint of the floating detachment link removed from the proximal end of the coil was bent [ Figure 3e ].


Figure 3:

Bench-top experiment using aneurysm model: (a) Silicone aneurysm with Axium coil inserted through Phenom 17. The tip of the Phenom 17 is aligned with the junction (rectangle). The tip of the Phenom 17 tip is compressed against the aneurysm wall, resulting in an excessively bent junction. (b) Magnified view of the rectangle area in Figure 3a. (c) After a detachment attempt, the delivery pusher and the proximal end of the coil remain engaged. (d) Pulling the delivery pusher releases the engagement, and the coil detaches from the delivery pusher. The floating detachment link is not retracted into the coil and remains visible at the proximal end of the coil (white arrowhead). (e) The ball joint of the floating detachment link removed from the proximal end of the coil is bent.

 

Patient informed consent

The necessary patient informed consent was obtained in this study.

DISCUSSION

This case is a rare instance of coil-related complications similar to unraveling and knotting. This is the first report to elucidate the mechanism of coil sticking based on intraoperative imaging findings and bench-top experiments, which appears to be caused by an excessively bent junction of the coil and the delivery pusher.

The Axium coil is a mechanically detachable coil. According to the manufacturing data, it has a floating detachment link with a ball joint [ Figure 4a ]. There is a circular opening at the tip of the delivery pusher that holds the ball joint of the floating detachment link in place with a release wire because the diameter of the ball joint is slightly smaller than that of the circular opening. This ball joint allows the junction to bend to some degree and rotate 360 degrees. By attaching the release wire connector at the proximal end of the delivery pusher to an instant detacher and pulling the slide knob back, the release wire is retracted from the circular opening into the delivery pusher, causing the ball joint to detach from the circular opening [ Figure 4b ].


Figure 4:

Diagram of coil sticking mechanism: The tip of the delivery pusher tip (left) and the proximal end of the coil (right). (a) Axium coil before detachment. The floating detachment link has a ball joint (*) whose diameter (white bidirectional arrow) is slightly smaller than the diameter of the circular opening (red bidirectional arrow). A release wire (black arrow) located in the circular opening holds the ball joint in place. (b) Axium coil after detachment. The release wire is retracted into the delivery pusher and the ball joint of the floating detachment link detaches from the circular ring. The floating detachment link is then retracted into the proximal end of the coil. (c) Axium coil in this case before the detachment attempt. The ball joint of the floating detachment link is bent. (d) Axium coil in this case after the detachment attempt. The ball joint of the floating detachment link hooks into the circular opening, preventing the proximal end of the coil from disengaging from the delivery pusher.

 

Coil sticking within the microcatheter usually occurs when the tip of the delivery pusher and the proximal end of the coil overlap and engage within the microcatheter.[ 14 ] In this case, given the internal diameter of the microcatheter (0.017 inches) and the diameters of the coil (0.0115 inches) and the delivery pusher (0.014 inches), such a problem is unlikely to occur. If such a problem occurs, the operator may feel resistance during the push-pull movement of the delivery pusher. In this case, however, the operator felt no such resistance, suggesting that the coil sticking was caused by some other mechanism. Experiments demonstrated that (1) when the junction of the coil and the delivery pusher is excessively bent, detachment attempts may fail; (2) in such a case, the ball joint of the floating detachment link is also bent and is not retracted into the proximal end of the coil; and (3) forcibly advancing the microcatheter while the tip of the microcatheter is aligned with the junction may cause excessive bending of the junction. In this case, the Phenom 17 was compressed against the coil mass while aligned with the junction [ Figure 1d ], which appears to have caused excessively bending of the junction of the coil and the delivery pusher. Initially, it was thought that the coil sticking in this case was caused by a malfunction of the instant detacher, and several detachment attempts were made. It is likely that the floating detachment link became bent during coil insertion [ Figure 4c ]. Even after the release wire was retracted from the circular opening into the delivery pusher, the ball joint of the floating detachment link hooked into the circular opening and the coil and the delivery pusher remained engaged [ Figure 4d ]. When the delivery pusher was pulled, the coil followed the delivery pusher [ Figure 1e ]. The proximal end of the coil became dislodged within the Phenom 17 due to factors such as the degree of bending of the junction and the pulling force and speed. In aneurysm model experiments, similar movements of the coil following the delivery pusher were observed, but the coil was detached from the circular opening with minimal movement and the coil did not follow the delivery pusher into the microcatheter. In this case, however, there was concern that repeated detachment attempts could lead to thrombus formation and increased blood viscosity at the circular opening and continued coil sticking.

The mechanism of coil sticking in this case appears to be specific to the Axium coil that has a floating detachment link with a ball joint. When using Axium coils, the microcatheter tip against should not be pressed against the coil mass, as alignment with the junction may cause excessive bending of the junction. During the initial and final stages of coil insertion, the position of the second marker on the microcatheter should be monitored to ensure that the microcatheter is not advanced too far into the aneurysm. In this case, when the coil was suspected of being stuck, the coil retrieved by pulling the delivery pusher and the coil unexpectedly detached from the circular opening and became dislodged within the microcatheter. After retraction of the delivery pusher, flushing the microcatheter with heparinized saline was performed under non-fluoroscopic guidance. Subsequent fluoroscopy showed that the dislodged coil had settled within the aneurysm. In this case, the aneurysm neck was relatively narrow and the coil was inserted into the aneurysm by simply advancing it. The length of coil withdrawn from the aneurysm was 2 cm and most of the coil (6 cm) remained within the aneurysm. We therefore gently pushed the coil into the aneurysm with a microguidewire so that the coil could be advanced but not retracted into the microcatheter. If the shape of the aneurysm allows for simple advancement of a short coil into the aneurysm, pushing the coil with a microguidewire is considered a good approach; if the shape of the aneurysm shape does not allow for simple advancement of the coil or if the coil is relatively long, it is better to retrieve the coil. In such a case, applying suction to the microcatheter and gently pulling the microcatheter and coil together may hold them together. If the coil does not fully settle within the aneurysm and prolapses into the parent vessel, ischemic complications may occur.[ 2 , 7 , 15 ] If the degree of coil prolapse is less than half the diameter of the parent vessel, antiplatelet therapy alone may be sufficient to prevent thromboembolic events.[ 2 ] If the prolapsed coil is near the vessel wall, enhanced antiplatelet therapy with close monitoring should be administered.[ 4 , 5 , 12 ] However, it has been reported that even with enhanced antithrombotic therapy, diffusion-weighted magnetic resonance imaging showed abnormalities in 50% of cases with coil prolapse and symptomatic complications occurred in 29% of cases with coil prolapse.[ 15 ] Since the risk of thromboembolic events remains even with enhanced antiplatelet therapy, retrieval of the prolapsed coil is desirable. Reported retrieval methods include using a snare[ 6 ] or hooking the coil with a microguidewire bent into a pigtail shape.[ 11 ] In cases where coil retrieval is difficult, pressing the proximal end of the coil against the vessel wall with a stent may be useful.[ 1 ] Flushing the microcatheter with heparinized saline may cause the coil to prolapse into the parent vessel or even into more distal vessels, which may require coil retrieval or stent placement may be needed.

CONCLUSION

When using coils with a floating detachment link that has a ball joint, forcibly advancing the microcatheter while the tip of the microcatheter is aligned with the junction may cause excessive bending of the junction, resulting in coil sticking.

Ethical approval:

The Institutional Review Board approval is not required.

Declaration of patient consent:

The authors certify that they have obtained all appropriate patient consent

Financial support and sponsorship:

Nil.

Conflicts of interest:

Dr. Ikeda reports lecturer’s fees from Medtronic, DaiichiSankyo, Johnson and Johnson, Terumo, Stryker Japan.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation:

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.

Acknowledgments:

We would like to thank Ms. Miho Kobayashi for the English language review.

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