Location and Formation of the Interscalene Triangle
The space is situated between the anterior and middle scalene muscles.
Borders:
- Anterior: Anterior scalene muscle (m. scalenus anterior).
- Posterior: Middle scalene muscle (m. scalenus medius).
Fascial Cover: The space is covered by the prevertebral fascia. This fascia forms sheaths for the scalene muscles, which originate from the transverse processes of the cervical vertebrae. Extensions of the prevertebral fascia extend onto the nerve plexus trunks and the subclavian artery, forming their fascial sheaths.
Structures Passing Through the Interscalene Triangle
The space contains the following neurovascular structures:
- Subclavian artery (a. subclavia) — enters the space at the level of the first rib. Its second anatomical part lies within this space. As it passes here, the artery creates the subclavian groove (sulcus a. subclaviae) on the superior surface of the first rib.
- Costocervical trunk (truncus costocervicalis) — a branch of the second part of the subclavian artery.
- Cervical plexus (plexus cervicalis) — its structures are formed within this space.
- Brachial plexus (plexus brachialis) — also formed within this space.
Topography and Adjacent Structures
The interscalene triangle is related to several other topographic regions of the neck:
- Scalene hiatus / anterior scalene space (spatium antescalenum) — located anterior to the anterior scalene muscle.
- First part of the subclavian artery — the segment of the vessel from its origin to the entrance into the interscalene space. At this stage, the thyrocervical trunk (truncus thyrocervicalis) branches off — a short vessel (1–1.5 cm) originating from the anterosuperior wall of the artery before it enters the space.
- Third part of the subclavian artery — begins at the lateral border of the anterior scalene muscle and extends to the clavicle. The combined length of the second, third, and fourth parts of the artery is 5–7 cm on both the right and left sides.
- Prevertebral space — a closed space located posterior to the prevertebral fascia. It is filled with the longus colli and longus capitis muscles and is bounded laterally by the transverse processes of the cervical vertebrae.