European Journal of Translational and Clinical Medicine


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Late postoperative slippage of the cerebral aneurysm clip. A systematic review and meta-analysis

Tomasz Szmuda, Paweł Słoniewski

DOI: 10.31373/ejtcm/103442
Eur J Transl Clin Med 2019 (vol. 2), No. 1: 56-69
Publication date: 2019-06-04
e-ISSN: 2657-3156
Language: en


A late clip slippage from the previously properly secured cerebral aneurysm is rarely observed. To date these complications have not pooled and evaluated using systematic review methodology. The objective was to report factors attributed to the late slippage of the aneurysm clip in the postoperative period.

Material and methods
All causes of postoperative clip slippage were systematically reviewed and analysed according to PRISMA Individual Patient Data protocol. Medline (PubMed), Embase, Cochrane, ISI Web of Knowledge and Google Scholar were searched for all relevant cases.

Systematic review of the literature yielded 105 original cases proving slipped clip in the postoperative period. The slipped clip caused bleeding in 53.8% of patients. The putative cause of clip slippage was provided in only 34.7% of the published cases. If a single clip was used, then complete clip slippage was noted more often (p=0.04). Multiple clipping and clip-wrapping techniques were postulated as ways to prevent postoperative clip slippage.

The reason for late slippage of the aneurysm clip remains unexplained by most authors. Based on systematic reviewing, the use of tandem of clips prevents their late migration off the aneurysm. Clipping with wrapping or use of a single clip reinforced by any wrapping material seems a more durable solution.

intracranial aneurysm; clip slippage; neurosurgical clipping; systematic review


Postoperative clip slippage is a rarely observed complication. Authors attributed this complication to the application of a short clip, some alloy features or clip closing pressure [1,2]. Repetitive opening of the clip further reduces its closing forces [3–5]. Another factor is the so-called scissoring effect [6–9]. Various authors demonstrated the examples of late clip migration following seemingly successful operations [10–13]. Less than 1% of the postoperative angiograms show an insufficiently secured aneurysm or a rotated clip [14]. Authors demonstrated various techniques in order to avoid clip slippage, although their interests were focused on the particular operative environment. Hundreds of case reports that were never critically appraised. To date, cases of clip slippage have not been pooled and analysed using a validated systematic review methodology. We aimed to collect and summarize the existing literature about clip slippage phenomena using the reproducible and widely accepted PRISMA Statement methodology [15].

Methods and materials

After reaching consensus, the authors developed a detailed protocol [16]. One author searched (November 2017), selected the articles and extracted data. Online Medline, Embase, Web of Knowledge, Cochrane and Google Scholar engines were queried for phrase: ‘aneurysm’ AND (‘clip’ OR ‘clipping’) AND (‘slip’ OR ‘slippage’). Duplicating records were removed using Mendeley Software (ver.1.17.10). Screening was based on titles and abstracts. We accepted original case reports, reviews, commentaries, expert opinions including animal, technical studies, PhD dissertations and patents. No limits in time of publication or language were applied. Google Translate website was used in case of abstracts and articles not in English. Following eligibility assessment, extensive searches for relevant references followed data extraction. Two types of data were deemed valid for further narrative synthesis of evidence: (1) descriptions of postoperative clip slippage and (2) intraoperative manoeuvres intended for prevention of a late slip-off phenomena. Raw data from each patient (Individual Participant Data method, IPD) were analysed as if all slippage occurrences belonged to an assumed single cohort. The evaluation was performed in accordance to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement for IPD systematic reviews, which included search, eligibility, extraction, and reporting [17]. Publication bias was not assessed.

We used typical statistical methods for relevant comparisons: chi-square, t-test or Mann-Whitney U test. Probability value less than 0.05 was considered significant. Statistica v. 13.1 (StatSoft Co, Tulsa, OK; USA) and Prism (GraphPad Software, La Jolla, CA; USA) were used. IRB Committee in the institution of systematic reviews is exempt.


The literature search yielded 3034 records, mostly identified via Google Scholar which explores full-texts for keywords. ‘Slip’ unrelated to cerebral aneurysm was the main exclusion criterion. Finally, 139 studies were included for the synthesis. 

(Figure 1)


Fig. 1. Flowchart depicting the strategy for literature search. Cumulative number of cases involving aneurysm clip slippage. The graph demonstrates the constantly increasing publication rate on this subject. 

From: Moher D, Liberati A, Tetzlaff J, Altman DG, The PRISMA Group (2009). Preferred Reporting Items for Systematic Reviews and Meta-Analyses: The PRISMA Statement. PLoS Med 6(7): e1000097.


We found 105 original cases reporting late clip migration. In a half of the cases the slipped clip caused bleeding (53.8%; 43/80), half of which were fatal (23/43). A routine postoperative angiography revealed the incidental clip displacement in 32.5% of cases (26/80). Anterior communicating artery (n=15), internal carotid artery (n=21, including 2 blister-like), middle cerebral artery (n=12) and basilar artery (n=7) were commonly encountered locations. In majority of cases (65.3%; 62/95) the authors were not able to provide any reason for clip slippage. Others blamed the defect of clip material in 15 patients (16.0%) and persistent arterial pulsation in 6 (6.4%). Surprisingly, specific features of the particular aneurysm were attributed to only 5 cases of slipped clips (5.3%). 


(Supplementary Table 1)

Download file with the Supplementary Table 1


The published reports rarely included aneurysm size, usually only if the aneurysm was giant (85.0%; 8/10). In a quarter of the slippage cases more than one clip was applied (23.3%; 10/43). In 82.9% of cases (68/80) a clip completely slipped off the aneurysm dome. Aneurysm location (p=0.65), size (p=0.26), rebleeding as the first symptom (p=0.65), fatal rebleeding (p=0.89) and occurrence in postoperative DSA (p=0.52) were not related to the degree (complete or incomplete) of clip migration. On the other hand, complete clip slip-off was significantly more often encountered if a single clip was used (82.1% vs. 44.4%, p=0.04). Regarding the direction of slip, in 87.5% of reports the clip migrated off the aneurysm (87.5%; 70/80), whereas in 8 cases (11.4%) the clip was displaced down onto the parent vessel, causing cerebral ischemia in 3 patents (37.5%). 

Out of the 139 studies, 78 (56.1%) provided at least one suggestion on how to avoid late clip migration. The most commonly suggested method was placing several clips instead of one (15.8%; 24/139), followed by applying of clip-wrapping technique (7.2%p; 10/139) and performing DSA shortly after clipping (4.3%; 6/139). The suggested preventive methods were location-specific, e.g. in case of blood blister-like aneurysm authors postulated placing clips parallel to ICA or clip-wrapping. 


Our systematic review was divided into two stages: we pooled all valid cases in which an aneurysm clip slid off and collected all studies addressing prevention of clip slippage. By including every type of study into the systematic review, we intended to reveal case reports and authors’ own experiences. However, most authors (65.3%) did not provide any reason why the clip slipped off. The incomplete clipping and insufficient amount of used clips were the most commonly stated reasons. On the other hand, tandem clipping seems more durable option proposed by 15.8% of authors in our systematic review [9,18–20]. 

The prevention of clip slippage depended on aneurysm location. Specifically, reinforcing with any wrapping material, clip-wrapping methods and placing blades parallel to carotid were proposed in blood blister-like aneurysms [21–25]. Whereas in cases of a clip slipped from ACoA aneurysm, the authors did not provide any suggestions for repair. 

Our systematic review pooled reports of slipped cerebral aneurysm clips. Based on this cohort we concluded that by using a single clip the surgeon should consider aneurysm recurrence. It was often speculated in the literature that multiple clipping more seems to be a more durable solution. Plenty of valuable hints on how to avoid postoperative clip slippage were suggested in the literature and we listed all of them based on the specific aneurysm location.

Ethical approval

Formal consent is not required for this type of stud.

Informed consent 

Informed consent was obtained from all individual participants included in the study.