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# Subclavius

The subclavius is a small muscle under the collarbone; it steadies the collarbone against the breastbone and cushions the vessels below.

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## What it is

A small muscle under the collarbone.

## What it does

Steadies the collarbone against the breastbone.

## Key points

- Lies between the clavicle and the subclavian vein: in a midshaft clavicle fracture it partly cushions the subclavian vessels and the brachial plexus from the bone ends
- Its tendon, with the costoclavicular ligament and the first rib, can squeeze the subclavian vein in the costoclavicular space (venous thoracic outlet syndrome, effort thrombosis)
- Enclosed by the clavipectoral fascia, which continues down to the [pectoralis minor](https://durgical.com/en/anatomy/pectoralis-minor-muscle/)

## Key facts

**Origin**
Junction of the 1st rib and its cartilage

**Insertion**
Inferior surface of the middle third of the clavicle

**Action**
Anchors and depresses the clavicle

**Nerve**
[Nerve to subclavius](https://durgical.com/en/anatomy/subclavian-nerve/) (C5–C6)

**Blood supply**
[Thoracoacromial artery](https://durgical.com/en/anatomy/thoracoacromial-artery/) (clavicular branch)

## Relations

**Above**
The groove on the underside of the middle third of the [clavicle](https://durgical.com/en/anatomy/clavicle/)

**Below**
The [subclavian vein](https://durgical.com/en/anatomy/subclavian-veins/), with the [subclavian artery](https://durgical.com/en/anatomy/right-subclavian-artery/) and the [brachial plexus](https://durgical.com/en/anatomy/roots-of-brachial-plexus/) behind it, all crossing the [first rib](https://durgical.com/en/anatomy/first-rib/)

**In front**
The clavipectoral fascia and the clavicular head of the [pectoralis major](https://durgical.com/en/anatomy/pectoralis-major-muscle/)

**Medial**
The [costoclavicular ligament](https://durgical.com/en/anatomy/costoclavicular-ligament/), near its origin at the first rib and its cartilage

## How to find it

Not palpable: it hides in the groove under the clavicle. In dissection it appears on dividing the clavipectoral fascia below the clavicle; on ultrasound it is the thin band between the clavicle and the subclavian vein.

## Examination

- Costoclavicular (military brace) test: the shoulders are drawn back and down while the radial pulse is felt; loss of the pulse or reproduced symptoms suggests compression between the clavicle with the subclavius and the first rib, though many healthy people also lose the pulse

## On imaging

A small muscle under the clavicle, seen on CT or MRI between the bone and the subclavian vein. In venous thoracic outlet syndrome, studies with the arm raised (Doppler ultrasound, CT or MR venography) show the vein narrowed in the costoclavicular space; Doppler ultrasound is the first test for subclavian vein thrombosis.

## Clinical notes

- Drilling and plating the clavicle put the subclavian vessels at risk; the subclavius is the only soft tissue between the bone and the vein
- Surgery for venous thoracic outlet syndrome resects the first rib and divides the subclavius tendon and costoclavicular ligament to free the vein

## Anatomical variants

- An accessory [phrenic nerve](https://durgical.com/en/anatomy/phrenic-nerve/) often arises from the nerve to subclavius and joins the phrenic nerve in the [chest](https://durgical.com/en/anatomy/region/chest/) (frequency varies between studies)

## Related conditions

- [Thoracic outlet syndrome](https://durgical.com/en/conditions/thoracic-outlet-syndrome/)

## Test yourself

Think of the answer, then tap the question to see it.

## What does the subclavius do in a midshaft clavicle fracture?

Lying between the clavicle and the subclavian vein, it partly cushions the subclavian vessels and the brachial plexus from the bone ends.

## How can the subclavius cause venous thoracic outlet syndrome?

Its tendon, with the costoclavicular ligament and the first rib, can squeeze the subclavian vein in the costoclavicular space (effort thrombosis).

## What are the attachments and nerve supply of the subclavius?

From the junction of the 1st rib and its cartilage to the underside of the middle third of the clavicle; nerve to subclavius (C5–C6).

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Educational information, not medical advice. For any symptom, see a health professional.

## Its names

**Official Latin (TA2)**
musculus subclavius TA2 2306

**Official Spanish (DeCS)**
Músculo subclavio

**English (TA2)**
Subclavius

## Related

- [Nerve to subclavius](https://durgical.com/en/anatomy/subclavian-nerve/)
- [Thoracoacromial artery](https://durgical.com/en/anatomy/thoracoacromial-artery/)
- [Clavicle](https://durgical.com/en/anatomy/clavicle/)
- [First rib](https://durgical.com/en/anatomy/first-rib/)

Sources: Terminologia Anatomica (TA2); [Anatomy, Shoulder and Upper Limb, Pectoral Muscles](https://www.ncbi.nlm.nih.gov/books/NBK545241/).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/anatomy/subclavius/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/subclavius/