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M01.04.002 Posterior Triangle
The posterior triangle of the neck is a clinically significant area located on the posterolateral aspect of the neck. It contains essential structures such as muscles, veins, arteries, and nerves. This article provides a comprehensive overview of its borders, contents, and clinical relevance for medical students.
Borders of the Posterior Triangle
The posterior triangle of the neck is defined by three primary borders:
| Border | Description |
|---|---|
| Anterior | Posterior border of the sternocleidomastoid (SCM) |
| Posterior | Anterior border of the trapezius muscle |
| Inferior | Middle 1/3 of the clavicle |
- Roof: Formed by the investing layer of fascia.
- Floor: Formed by the prevertebral fascia, which covers various muscles.
Contents of the Posterior Triangle
Muscles
Several muscles are found within the posterior triangle, contributing to its borders and floor:
| Muscle | Description |
|---|---|
| Omohyoid | Divided into superior and inferior bellies, crossing the posterior triangle. |
| Splenius Capitis | Part of the floor, covered by prevertebral fascia. |
| Levator Scapulae | Forms part of the floor, covered by prevertebral fascia. |
| Scalenes (Anterior, Middle, Posterior) | These muscles form the floor, covered by prevertebral fascia. |
Vasculature
The following vessels are located in the posterior triangle:
| Vessel | Description |
|---|---|
| External Jugular Vein | Formed by the retromandibular and posterior auricular veins, entering the posterior triangle. |
| Subclavian Vein | Often accessed for central venous catheterization. |
| Subclavian Artery | The distal part is located between the anterior and middle scalene muscles, becoming the axillary artery. |
| Transverse Cervical Vein | Located in the posterior triangle alongside their respective arteries. |
| Suprascapular Vein | Found in the posterior triangle, accompanying its respective artery. |
Clinical Relevance
External Jugular Vein
- Risk of Injury: The external jugular vein runs superficially and is vulnerable to damage in neck trauma.
- Medical Emergency: If severed, air can enter the vein due to the investing fascia, leading to cyanosis and disruption of blood flow. Immediate pressure must be applied to stop bleeding and prevent air embolism.
Nerves
The posterior triangle contains several vital nerves, including:
| Nerve | Function/Path |
|---|---|
| Accessory Nerve (CN XI) | Innervates the sternocleidomastoid and trapezius, traverses the posterior triangle, vulnerable to injury. |
| Cervical Plexus | Provides cutaneous and motor innervation to the neck, including the phrenic nerve, which innervates the diaphragm. |
| Brachial Plexus Trunks | Cross the floor of the posterior triangle, providing innervation to the upper limb. |
Cervical Plexus Block
- Application: A cervical plexus block can be used for anesthesia in neck procedures.
- Technique: Local anesthetic is injected at the junction of the superior and middle thirds of the SCM, known as the nerve point of the neck.
Subdivisions of the Posterior Triangle
The posterior triangle is divided into two sub-triangles by the omohyoid muscle:
| Sub-Triangle | Description |
|---|---|
| Occipital Triangle | Superior to the omohyoid, contains important nerves and vessels. |
| Subclavian Triangle | Inferior to the omohyoid, contains the distal part of the subclavian artery. |
Points to Remember
- The posterior triangle of the neck is an important anatomical area with a variety of structures.
- The external jugular vein and accessory nerve are particularly vulnerable to injury.
- The omohyoid muscle divides the posterior triangle into two sub-triangles: Occipital and subclavian.
- A cervical plexus block is a common technique for anesthesia in neck surgeries.