What is the axillary portion of ribs?

The axillary region (also known as the arm pit) is a pyramid-shaped area located between the shoulder girdle and thorax. It serves as a space for neurovascular and lymphatic structures to travel through to reach the upper extremity from the neck[1].

Structure/Borders[edit | edit source]

The structure of the axilla is dependent upon the position of the upper extremity - an expansive region when the arm is elevated and minimized when adducted[2].

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Contents[edit | edit source]

The axillary artery is an extension of the subclavian artery, and is called so after passing the first rib. It is renamed and considered the brachial artery after passing the teres major and exiting the axilla. The artery is encompassed by the axillary sheath and the brachial plexus cords and branches. The axillary artery is divided into three parts with arterial branches associated with each section. The branches of the axillary artery include the superior thoracic, thoracoacromial, lateral thoracic, subscapular, anterior humeral circumflex and posterior humeral circumflex arteries. The scapular and humeral anastomoses created by these branches are important factors to compensate if there are any occlusions of the axillary artery[3].

The brachial plexus' cords and branches surround the axillary artery and are named in reference to their position relative to the artery. The nerves of the brachial plexus course past the first rib, inferior to the clavicle and through the axilla from its cervical and thoracic roots (C5-T1) towards its peripheral innervation destinations. Within the axillary region, the brachial plexus gives rise to peripheral nerves, including the medial and lateral pectoral, medial cutaneous of arm and forearm, upper and lower subscapular, and thoracodorsal nerves, supplying muscles of the shoulder girdle and chest as well as sensation to certain areas of the upper extremity[2].

Medial to the axillary artery lies the axillary vein, receiving deoxygenated blood from the cephalic vein, basilic vein, and other tributaries correlating with branches of the axillary artery, ultimately serving as the major vessel of drainage for the upper extremity[1][2]. The axillary vein becomes the subclavian vein after exiting the apex of the axilla. Like the axillary artery, the axillary vein features anastomoses to compensate for any blockages that may form[2].

Axillary lymph vessels and nodes process lymph from the upper extremity and chest. The superficial vessels drain the skin while the deep vessels drain the bones and muscles. There are five groups of axillary nodes present in the axilla including pectoral, lateral, posterior (subscapular), central, and apical[3].

In addition to the neurovascular bundle, the axillary region also contains the short head of the Biceps Brachii muscle, coracobrachialis muscle, fascia and adipose tissue. Mammary tissue is also possibly present[2].

Clinical Relevance[edit | edit source]

• Thoracic Outlet Syndrome (TOS) results from the compression of nerves and/or vessels at or around the apex of the axilla. The clinical presentation and distribution of TOS is dependent upon the structures compressed. A patient with TOS may complain of ipsilateral upper extremity pain, parasthesia, paresis, discoloration, and/or cold sensitivity[3]. See the content page on TOS for more information.

• The breast is mostly drained through the axillary lymph vessels and nodes. Breast cancer can spread to the surrounding lymphatic system as well as the pectoralis major muscle and it's fascia. Decreased filtration of the axillary lymph nodes from cancerous infiltration, damage, or surgical removal as a form of treatment can result in swollen axillary lymph nodes or upper extremity lymphedema[3]. An additional risk of surgical removal is the damage of the long thoracic nerve, which would clinically present as scapular winging due to the resulting denervation of the serratus anterior muscle[1].

• If the neck or upper extremity is forcefully stretched or trauma is inflicted upon the axillary region a brachial plexus injury may result. The clinical presentation of a brachial plexus injury is dependent upon the specific nerves and nerve roots damaged. It results in loss or diminishment of sensation and motor control of the associated innervation of the nerve(s) damaged. Upper trunk injuries (C4-C6) are more common than lower trunk injuries (C7-T1). Brachial plexus injuries may also be a result of a cervical rib or apical lung cancer growth[3]. See the content page on brachial plexus injuries, Erb's palsy, and Klumpke's palsy for more information.

• If not properly fit, positioned and trained, axillary crutches can cause unnecessary pressures and damage to the contents of the axilla[3]. A clinician should also consider which type of crutch (axillary, forearm, gutter) or assistive device is most appropriate for the patient. See the content page on crutches for more information of proper fitting.

Related Pages[edit | edit source]

References[edit | edit source]

The ribs are a set of twelve paired bones which form the protective 'cage' of the thorax. They articulate with the vertebral column posteriorly, and terminate anteriorly as cartilage (known as costal cartilage).

As part of the bony thorax, the ribs protect the internal thoracic organs. They also have a role in ventilation; moving during chest expansion to enable lung inflation.

In this article, we shall look at the anatomy of the ribs  - their bony landmarks, articulations and clinical correlations.

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Rib Structure

There are two classifications of ribs - atypical and typical. The typical ribs have a generalised structure, while the atypical ribs have variations on this structure.

Typical Ribs

The typical rib consists of a head, neck and body:

The head is wedge shaped, and has two articular facets separated by a wedge of bone. One facet articulates with the numerically corresponding vertebra, and the other articulates with the vertebra above.

The neck contains no bony prominences, but simply connects the head with the body. Where the neck meets the body there is a roughed tubercle, with a facet for articulation with the transverse process of the corresponding vertebra.

The body, or shaft of the rib is flat and curved. The internal surface of the shaft has a groove for the neurovascular supply of the thorax, protecting the vessels and nerves from damage.

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Atypical Ribs

Ribs 1, 2, 10 11 and 12 can be described as 'atypical' - they have features that are not common to all the ribs.

Rib 1 is shorter and wider than the other ribs. It only has one facet on its head for articulation with its corresponding vertebra (there isn't a thoracic vertebra above it). The superior surface is marked by two grooves, which make way for the subclavian vessels.

Rib 2 is thinner and longer than rib 1, and has two articular facets on the head as normal. It has a roughened area on its upper surface, from which the serratus anterior muscle originates.

Rib 10 only has one facet - for articulation with its numerically corresponding vertebra.

Ribs 11 and 12 have no neck, and only contain one facet, which is for articulation with their corresponding vertebra.

Articulations

The majority of the ribs have an anterior and posterior articulation.

Posterior

All the twelve ribs articulate posteriorly with the vertebra of the spine. Each rib forms two joints:

• Costotransverse joint - Between the tubercle of the rib, and the transverse costal facet of the corresponding vertebra.

• Costovertebral joint - Between the head of the rib, superior costal facet of the corresponding vertebra, and the inferior costal facet of the vertebra above.

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  Fig 3 - Posterior articulations between a typical rib and its numerically corresponding vertebra.[/caption]

Anterior

The anterior attachment of the ribs vary:

• Ribs 1-7 attach independently to the sternum.
• Ribs 8 - 10 attach to the costal cartilages superior to them.
• Ribs 11 and 12 do not have an anterior attachment and end in the abdominal musculature. Because of this, they are sometimes called 'floating ribs'.

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Clinical Relevance: Rib Fractures

Rib fractures most commonly occur in the middle ribs, as a consequence of crushing injuries or direct trauma. A common complication of a rib fracture is further soft tissue injury from the broken fragments. Structures most at risk of damage are the lungs, spleen or diaphragm.

If two or more fractures occur in two or more adjacent ribs, the affected area is no longer under control of the thoracic muscles. It displays a paradoxical movement during lung inflation and deflation. This condition is known as flail chest. It impairs full expansion of the ribcage, thus affecting the oxygen content of the blood. Flail chest is treated by fixing the affected ribs, preventing their paradoxical movement.

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