Boundaries and anatomical position
The lateral cervical triangle (trigonum colli laterale) is divided into two unequal parts by the inferior belly of the omohyoid muscle (m. omohyoideus). The upper, larger section forms the omotrapezoid triangle, and the lower, smaller area forms the omoclavicular triangle (trigonum omoclaviculare).
The anatomical boundaries of the omoclavicular triangle are extremely clear:
- Superiorly: inferior belly of the omohyoid muscle.
- Inferiorly: clavicle.
Visually on the body surface, this area projects as the greater supraclavicular fossa.
Layer-by-layer topography and fasciae
Surgical access in the omoclavicular triangle requires an understanding of its strict layer-by-layer structure:
- Skin: noted for its thinness and high mobility.
- Platysma (m. platysma): covers the area only partially, specifically in its anteroinferior section.
- Subcutaneous tissue: contains the supraclavicular nerves (nn. supraclaviculares mediales, intermedii et laterales). These branches of the cervical plexus provide sensory innervation to the skin of the neck and shoulder girdle. The lesser occipital nerve (n. occipitalis minor) also ascends along the posterior border of the sternocleidomastoid muscle. Superficial lymph nodes running along the external jugular vein may be found within the adipose tissue.
Features of the fascial apparatus: Below the level of m. omohyoideus, the topography of the fasciae is specific. Here lie the omoclavicular (3rd) fascia, and immediately deep to it, the prevertebral (5th) fascia. The fifth fascia plays a critical role in forming deep structures: it creates dense sheaths for the scalene muscles (mm. scaleni), attaches to the 1st and 2nd ribs, and forms a protective sheath for the subclavian artery and the trunks of the brachial plexus.
Topography of vessels and nerves
The main contents of the omoclavicular triangle include the third part of the subclavian artery (a. subclavia) and the supraclavicular part of the brachial plexus (plexus brachialis). The reciprocal arrangement (syntopy) of these structures is strictly defined: the nerve trunks of the brachial plexus lie superiorly and posteriorly to the artery.
Subclavian artery and its branches: The artery lies on the 1st rib. The primary landmark for isolating it is the scalene tubercle (tuberculum musculi scaleni anterioris): the vessel passes immediately lateral to it. Above the clavicle within the triangle, the following branches arise:
- a. suprascapularis (suprascapular artery);
- a. cervicalis superficialis (superficial cervical artery);
- a. transversa colli (transverse cervical artery).
The branches intertwine intricately with the trunks of the brachial plexus. The superficial cervical and suprascapular arteries run behind the upper border of the clavicle superficial to the nerve trunks. In contrast, the transverse cervical artery passes directly between the trunks of the plexus.
Subclavian vein (v. subclavia): The vein is located in the interscalene space, i.e., anterior to the anterior scalene muscle. It arches over the 1st rib medial to the corresponding artery, with its lower edge overlapping the artery. Clinically, it is crucial that between the clavicle and the 1st rib, the walls of the vein are firmly fused with the fascial sheath of the subclavius muscle and the cervical fasciae. Due to this fixation, the vein never collapses (gaping when injured). This anatomical property makes it an ideal target for puncture and percutaneous catheterization.
Briefly: answers to topical questions
What anatomical structures form the boundaries of the omoclavicular triangle?
The boundaries of the omoclavicular triangle (trigonum omoclaviculare) are formed by the clavicle and one of the neck muscles. This triangle is the smaller part of the lateral cervical triangle (trigonum colli laterale) and corresponds to the greater supraclavicular fossa (fossa supraclavicularis major).
Its anatomical boundaries include:
- Inferiorly — the clavicle.
- Superiorly — the inferior belly of the omohyoid muscle (m. omohyoideus).
In which topographical-anatomical space do the subclavian artery and brachial plexus run?
The subclavian artery and brachial plexus pass through the interscalene space (spatium interscalenum).
The following structures are located in this topographical-anatomical space:
- Subclavian artery (a. subclavia) — its second part is located here, lying on the 1st rib lateral to the scalene tubercle.
- Brachial plexus (plexus brachialis) — its trunks are located superiorly and posteriorly to the subclavian artery.
The interscalene space itself is bounded anteriorly by the anterior scalene muscle (m. scalenus anterior), posteriorly by the middle scalene muscle (m. scalenus medius), and inferiorly by the 1st rib.
To memorize the syntopy of the branches of the subclavian artery and the brachial plexus, use the "sandwich" analogy: the superficial cervical and suprascapular arteries lie on top (superficial to the trunks), while the transverse cervical artery acts as the filling, passing directly between the nerve trunks.
Class and exam questions
Where and how can a surgeon locate the subclavian artery in the omoclavicular triangle?
A reliable bony landmark is the scalene tubercle on the first rib. The subclavian artery lies on the rib immediately lateral to this formation.
Why is the subclavian vein preferred for central venous catheter placement?
Its walls are tightly fused with the fascial sheath of the subclavius muscle and the cervical fasciae. Because of this, the vein does not collapse and remains constantly patent, ensuring its easy accessibility for puncture.
Which fascia forms the sheath for the brachial plexus and subclavian artery?
The sheath for these structures, as well as the sheaths for the scalene muscles, is formed by the fifth (prevertebral) cervical fascia.
What else to study on this topic
- Boundaries and contents of the prescalene space
- Topography of the omotrapezoid triangle
- Formation of the brachial plexus trunks
- Clinical anatomy and branches of the cervical plexus
- Cervical fasciae according to Shevkunenko: a detailed review
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