Reliability of Sedillot’s triangle as a potential anatomical landmark for central venous catheter insertion: insights from cadaveric study

Abstract

Sedillot’s triangle (ST), formed between the sternal and clavicular heads of sternocleidomastoid (SCM) muscle, is often used as an anatomical landmark for internal jugular vein (IJV) cannulation, but its reliability has been questioned. This cadaveric study aimed to evaluate the effectiveness of ST in locating IJV. Dissections were performed on 23 adult cadavers (46 sides). ST was exposed, and a pin was inserted at its apex to assess its relationship with IJV. Dimensions of ST and distance between apex and IJV were measured (only in cases with unsuccessful puncture), along with IJV diameter at the apex. Showed that 92.00% of sides had a fully formed ST, while 8.00% (all left-sided) lacked a gap between the SCM heads. On right side, the needle corresponded directly with IJV in 19 (82.60%) cases, but missed laterally and medially in two (8.69%) cases each. On left side, successful IJV puncture occurred in 11 (61.11%) cases, with lateral and medial misses in five (27.77%) and two (11.11%) respectively. The mean height and width of ST was 64.30±7.86 mm and 20.08±6.26 mm on right side and 63.95±7.28 mm and 15.56±9.91 mm on left side. IJV diameter at the apex was significantly higher in male and on right side. Overall, right ST proved to be a reasonably reliable landmark for successful central venous catheter. However, anatomical variability, particularly on left side, suggests that caution should be exercised, and additional methods such as ultrasound guidance may improve the accuracy and safety of IJV cannulation using this approach.

Introduction

Central venous catheter (CVC) insertion is a crucial procedure in various medical settings, such as intensive care units, emergency departments, and surgical suites, as it provides direct access to the central venous circulation for administering medications, fluids, and hemodynamic monitoring. Despite its widespread use, CVC insertion poses risks, including arterial puncture, pneumothorax, and nerve damage, due to the proximity of critical structures [1]. Therefore, identifying reliable anatomical landmarks is essential to minimize these risks and ensure accurate catheter placement. Commonly used insertion sites include the internal jugular vein (IJV), subclavian vein, and femoral vein, each offering specific advantages [2]. Cannulating the IJV reduces the likelihood of catheter misplacement and the risk of injury to nearby neurovascular structures, with arterial puncture being a key concern due to the proximity of the common carotid artery. The IJV’s anatomy allows for easy pressure application in such cases and is also associated with a lower risk of infection [3, 4]. Han et al. [5] found higher success rates with IJV cannulation (89.7% for the right IJV, 79.4% for the left) compared to the subclavian veins. However, CVC insertion carries inherent risks, highlighting the need for thorough knowledge of the venous system and surrounding anatomy.

Historically, surface landmarks like the clavicle and sternocleidomastoid (SCM) muscle have been used to guide CVC placement, especially for the IJV and subclavian vein approaches. However, these landmarks can be unreliable in patients with anatomical variations or obesity. The central approach to IJV cannulation involves using Sedillot’s triangle (ST), defined by the sternal and clavicular heads of the SCM and the clavicle’s superior border [6]. Within the ST, successful identification of the IJV relies on multiple anatomical factors. These can be systematically categorized as follows: landmark visibility (clear identification of ST and neighbouring structures), variations in IJV anatomy (size, shape, and position of the vein within the triangle), depth of the IJV under the skin, side-specific differences, the right IJV is typically larger and straighter compared to the left, making it easier to identify and presence of prominent valves at the venous junction can occasionally complicate needle access. In this approach, a needle is inserted at the apex of ST at a 40°–45° angle, directed towards the ipsilateral nipple [7]. The patient is placed supine with shoulders supported and the head turned contralaterally.

Although ultrasound guidance has significantly improved the accuracy and safety of IJV cannulation, reducing complication rates [8], its availability and the need for specialized training limit its widespread use, particularly in low- and middle-income countries. Therefore, anatomical landmark techniques remain vital in many settings.

Different approaches to IJV cannulation, such as anterior, central, and posterior, have their own success rates and risks. While some studies reported similar outcomes between anterior and posterior approaches [9], recent findings indicate that the anterior approach, including ST-guided cannulation, may involve more attempts, longer procedure times, and higher complication rates. This raises concerns about whether the anterior approach should continue to be used.

Several cadaveric studies have investigated the use of ST as a landmark for CVC insertion, noting variations in success rates and complications [9, 10]. These studies have shown that ST provides a fairly reliable landmark, but the position and morphology of the IJV within the triangle are critical to the procedure’s success. Given these findings, further cadaveric research is needed to assess the reliability of ST as a guide for IJV cannulation in clinical practice. Our study focuses on evaluating the position and morphology of the IJV relative to ST, measuring the triangle’s dimensions, and mapping the IJV’s position and diameter within it.

Materials and Methods

The study sample consisted of 23 formalin-fixed adult cadavers (17 male and 6 female), aged between 55 and 75 years, with a mean age of 65 years. These cadavers, donated to the Department of Anatomy for research and teaching purposes, were selected after excluding those with any visible deformities, previous surgical procedures, or pathological conditions affecting the neck, thorax, or vascular structures. In the supine position, the anterior surface of each cadaver’s neck was carefully exposed. The skin, superficial fascia, and platysma muscle were reflected laterally to reveal the SCM muscle, including its sternal and clavicular heads. The SCM heads were then cleaned using blunt dissection to define the ST, which is bordered inferiorly by the clavicle and by the two heads of the SCM. The triangle was then outlined (Fig. 1).

Fig. 1.

Boundary of the Sedillot’s triangle (lined triangular area). Blue arrow, location of the internal jugular vein; SCM, sternocleidomastoid; c, clavicular head; s, sternal head; IBO, inferior belly of omohyoid; BP, underlying brachial plexus (supraclavicular part); EJV, external jugular vein; R, right; L, left; S, superior; I, inferior.

The dimensions of ST were measured using a sliding vernier caliper with 0.01 mm accuracy. The width was taken between the medial border of the clavicular head of the SCM (point A) and the lateral border of the sternal head of the SCM (point B). The height was measured from the midpoint of the triangle’s width (point C) to the apex where the two heads of the SCM meet (point D) (Fig. 2) [11].

Fig. 2.

Measurement of the dimensions of the Sedillot’s triangle. The width was taken between the medial border of the clavicular head of the SCM (C) (point A) and the lateral border of the sternal head of the SCM (S) (point B). The height was measured from the midpoint of the triangle’s width (point C) to the apex where the two heads of the SCM meet (point D). SCM, sternocleidomastoid; c, clavicular head; s, sternal head; R, right; L, left; S, superior; I, inferior.

Following this, the SCM was reflected while maintaining the position of the needles, allowing the IJV’s location relative to the needle at the ST apex to be observed and recorded. If the needle missed the IJV and was positioned either medially or laterally, the distance between the needle and the IJV midpoint was measured (Apex-IJV measurement). Additionally, the diameter of the IJV at the ST apex was measured, ensuring no compression of the vein walls. Two independent investigators recorded all measurements, and the mean of the two was calculated for further analysis.

Data were analyzed using IBM SPSS Statistics version 24 (IBM Co.). Descriptive statistics, including means, standard deviations, and ranges, were used to summarize the measurements. Variability in the distance from the triangle’s apex to the IJV was assessed to determine the landmark’s reliability. Sex differences in measurements were analyzed using independent t-tests, with significance set at P<0.05.

This study was done retrospectively on cadavers obtained through institutional body donation gramme for teaching and research purpose body in compliance with the institutional ethical standards.

Results

Among the 23 cadavers (46 sides), 41 sides showed (92.00%) fully formed STs with three clear borders, while five sides (8.00%) (all belongs to left) showed no gap between the two heads of the SCM and presented with a longitudinal groove that only had a height measurement (Fig. 3). The mean height and width of ST was 64.30±7.86 mm (range: 50.86–80.56 mm) and 20.08±6.26 mm (range: 12.35–35.66 mm) on right side and 63.95±7.28 mm (range: 50.23–78.37 mm) and 15.56±9.91 mm (range: 0.00–35.78 mm) on left side. Diameter of the IJV at the apex of the triangle showed significant differences both between male and female and sides, whereas, height of ST showed significant differences between male and female only (Table 1).

Fig. 3.

Showing no gap between the two heads of the SCM and presented with a shallow groove. Tip of red arrows are directed towards the shallow longitudinal groove thus formed. SCM, sternocleidomastoid; c, clavicular head; s, sternal head; R, right; L, left; S, superior; I, inferior.

Table 1.

Morphometric measurements of the Sedillot’s triangle

Parameter	Sample size (n)	Right side	Left side	P-value	Male	Female	P-value
ST height (mm)	46	64.30±7.86	63.95±7.28	0.582	66.14±6.56	58.41±7.25	0.007
ST width (mm)	41	20.08±6.26	15.56±9.91	0.212	17.44±8.09	18.91±9.90	1.000
Diameter of IJV (mm)	46	7.34±1.00	6.39±0.76	<0.001	7.17±0.92	6.00±0.67	<0.001
Apex-IJV distance (mm)a)	11	4.17±5.51	5.69±6.54	0.395	4.97±5.98	4.83±6.45	0.978

Values are presented as mean±SD. ST, Sedillot’s triangle; IJV, internal jugular vein. ^a)Cases where IJV did not correspond to the apex of the ST.

The needle corresponded to the IJV in 30 (73.17%) cases (Fig. 4). However, the topographic location of the IJV in terms of the needle inserted in the apex of the ST varies widely with sides of the neck. On the right side (23 cases), the needle corresponded directly with the IJV in 19 (82.60%) cases while the needle missed the IJV laterally and medially in 2 (8.69%) cases each. On the left side (18 cases with fully formed ST), the needle corresponded directly with the IJV in 11 (61.11%) cases while the needle missed the vein laterally in 5 (27.77%) and medially in 2 (11.11%). In terms of the location of the IJV relative to the apex of ST, chances of successful placement of needle were significantly higher on right side than the left.

Fig. 4.

Showing that the needle directly corresponded to the right internal jugular vein (IJV) at the level of the apex of the Sedillot’s triangle (yellow needle head). Blue arrow, location of the IJV; SCM, sternocleidomastoid; c, clavicular head; s, sternal head; IBO, inferior belly of omohyoid; SCV, subclavian vein; R, right; L, left; S, superior; I, inferior.

Discussion

This study explored the anatomical structure of the ST in relation to CVC insertion into the IJV, focusing on the efficacy of using the apex of ST as a guide for needle insertion. Numerous studies [9, 12, 13] have examined the use of the ST apex for successful CVC placement, with varying success depending on the side (right or left) and the type of approach. Consistent with the literature, the right IJV is typically preferred for catheterization [14]. Studies by Han et al. [5], Dunne et al. [12], and Botha et al. [15] have shown that the right IJV offers a more direct route to the superior vena cava. Han et al. [5] reported success rates of 89.7% on the right side and 79.4% on the left, while Botha et al. [15] reported rates of 97.14% on the right and 78.79% on the left. Dunne and colleagues [12] found a 71.4% success rate on the right compared to 52.5% on the left. In this study, we observed an 82.60% success rate for the right IJV and 61.11% for the left when using the ST apex as a landmark.

Contrary to these findings, Ayres et al. [11] found similar accuracy between the right and left sides, reporting ST alignment with the IJV in only 63% and 69% of cases, respectively. This difference may be due to their sample being neonatal cadavers, as most studies, including this one, were conducted on adult populations, potentially explaining the discrepancy. Age-related anatomical variations might account for the differences in success rates between studies.

In a comparison of landmark-based and ultrasound-guided approaches, over 90% of procedures favored the right side, regardless of technique [16]. The right IJV has several advantages over the left, including a more superficial location, easier ultrasound visualization, and a straighter path to the superior vena cava [6]. Additionally, cannulating the left IJV is associated with increased procedure time, more attempts, and higher risks of complications, such as injury to the thoracic duct or left common carotid artery [14, 16]. However, the improper formation or absence of ST on the left side has rarely been mentioned as a cause for left-sided CVC failure. In this study, we found five cases where the two heads of the SCM were not separated, instead presenting with a longitudinal groove, all of which occurred on the left side. This suggests that the central approach may not be the most reliable for blindly cannulating the left IJV, as difficulty locating the ST apex (or groove) contributed to needle mispositioning and inadvertent punctures.

Ayres et al. [11] localized ST only in 3 out of 38 sides of neonates (8%) which is slightly lower than observed in present study (11%) could be due to sample variation. They observed a groove in neonates rather than a well-formed ST due to developmental differentiation. They speculated that the outward growth of the clavicle, which could cause the muscle heads to separate and differentiated like adult as the infant matures. We did not examine the neonatal cadaver due to unavailability. Dunne et al. [12] later reported an absence of a fully formed ST in adult populations, which we also observed. Future research could investigate when the muscle heads separate to form the ST in living populations.

Of the landmark-based percutaneous techniques (anterior, posterior, and central) for IJV cannulation, the central approach—relying on ST anatomy—has the highest success rates [6]. This technique assumes the IJV runs anterolateral to the common carotid artery and beneath the ST apex, but variations in the IJV’s course can lead to unsuccessful punctures. In our study, we found that the IJV was not located at the ST apex in 18 cases (39.13%), with 12 lying lateral and 6 medial to the apex. In such cases, precise vein localization is crucial to avoid complications during CVC. Previous studies [11, 12, 17] have also reported instances where the IJV was outside the ST. We measured the distance between the ST apex and the IJV, and although most data on this are limited to neonatal populations [12], our findings provide valuable insights into the IJV’s topography at the apex.

The IJV’s diameter also plays a role in successful CVC placement, as a narrow vein decreases the chances of success even when correctly located. In this study, we found that the IJV was significantly wider on the right side in all the cases (Fig. 5), supporting the preference for the right IJV for manual CVC.

Fig. 5.

Box plot showing that the right internal jugular vein (IJV) was significantly wider on the right side in all the cases. Dot, represents outliner.

Denys and Uretsky (1991) [17] used ultrasound to assess anatomical variations and found that in 5.5% of 200 patients, the IJV deviated from the expected path based on external landmarks. Since the IJV is the most superficial structure within the carotid sheath, with the vagus nerve laterally and the common carotid artery medially, such misalignment increases the risk of accidental carotid artery puncture and severe complications.

In recent years, there has been increasing support for real-time ultrasound guidance in CVC procedures, as it reduces the number of attempts and shortens procedure time [18, 19]. While ultrasound is generally more successful than anatomical landmarks but, still a significant number of complications observed. Therefore, this landmark-based approach could be valuable not only in limited resource settings but also it will improve the success rate and reduce complication rate in ultrasound guided CVC cannulation.

Limitations

The small sample size restricts the generalizability of the findings, as anatomical variations may not be fully represented. Additionally, the cadaveric nature of the study limits its applicability to live patients, as the anatomy in preserved specimens may differ from that in living tissue due to changes in muscle tone, vascular filling, and tissue elasticity. The inability to palpate the common carotid artery before needle insertion further complicates the assessment of real-world procedural accuracy. Another limitation is the lack of investigation into the use of real-time ultrasound, which has become a standard tool for CVC placement in modern clinical practice.

In conclusion, this cadaveric study demonstrates that right ST is a reasonably effective anatomical landmark for locating the IJV, with successful IJV puncture achieved in 82.60% of cases. However, variability in IJV position was observed, with the vein being lateral to the apex of the triangle in 36.46% of cases and medial in 19.80%. Additionally, the absence of a gap between the sternal and clavicular heads of the SCM muscle in the left side further complicates the reliability of this approach. These findings suggest that while ST can serve as a useful guide, the inherent anatomical variations require caution during central venous catheterization to minimize complications. Further research, possibly involving ultrasound guidance, may be needed to improve the accuracy and safety of IJV cannulation using this method.

Funding Statement

Funding None.