First Rib

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Original Editor - Adam Vallely Farrell

Top Contributors - Kim Jackson, Maram Salem, Adam Vallely Farrell, Lucinda hampton, Evan Thomas, Kirenga Bamurange Liliane, Kai A. Sigel, WikiSysop and Mahbubur Rahman

Description

The first rib is the most superior of the twelve ribs. It is considered an atypical rib. It is an important anatomical landmark and borders of the superior thoracic aperture. The ribs form the main structure of the thoracic cage that protects the thoracic organs. There are 12 pairs of ribs which are separated by intercostal spaces. The first seven ribs progressively increase in length, the lower five ribs begin to decrease in length.  Ribs are highly vascular and trabecular with a thin outer layer of compact bone. Similar to the first rib, the 11th and 12th ribs are considered atypical ribs due to their anatomical features.

Anatomy

When compared to a typical rib, the first rib is

• Wide and short, consisting of a single articular facet for the costovertebral joint.
• Has a head, neck and shaft but lacks a discrete angle.
• Has a shaft that is indented laterally which serves as the groove for the subclavian artery.
• Has another groove for the subclavian vein anterior to the scalene tubercle.
• Lacks a costal groove on its inferior surface.
• The only rib that articulates with one thoracic vertebra only (T1).

The first rib has two tubercles. The first tubercle is the transverse tubercle, which is located posterior and lateral to the neck and bears an articular facet for the transverse process of T1. The second tubercle is the scalene tubercle, where the anterior scalene muscle inserts (otherwise known as the Lisfranc tubercle).

Blood Supply

The ribs receive their blood supply anterior via the anterior intercostal arteries and posteriorly by the posterior intercostal arteries.The anterior intercostal arteries branch off of the internal thoracic artery, which supply blood for the first seven ribs. The 8th, 9th, and 10th ribs anterior blood supply branches off the musculophrenic artery. All arteries and veins run through the costal groove of each rib.

• The internal thoracic artery supplies the anterior body wall and its associated structures from the clavicles to the umbilicus. It originates from the first part of the subclavian artery in the base of the neck.
• The superior intercostal arteries are formed as a direct result of the embryological development of the intersegmental arteries.
• These arteries are paired structures of the upper thorax which normally form to provide blood flow to the first and second intercostal arteries.
• Venous drainage is to the intercostal veins.

Innervation

The first rib is innervated by the first intercostal nerve.

• The intercostal nerves are part of the somatic nervous system, and arise from the anterior rami of the  T1 to T11 thoracic spinal nerves
• The intercostal nerves are distributed chiefly to the thoracic pleura and abdominal peritoneum and differ from the anterior rami of the other spinal nerves in that each pursues an independent course without plexus formation.
• The first intercostal nerve is joined to the brachial plexus through a branch, which is equivalent to the lateral cutaneous branches of remaining intercostal nerves.
• Another exception with the first intercostal nerve is that there is no anterior cutaneous branch. It is also very small as compared to the remaining nerves.

Attachments

The first rib has several attachments which are listed below;

• Anterior scalene muscle: scalene tubercle
• Middle scalene muscle: between groove for the subclavian artery and transverse tubercle
• Intercostal muscles: from the outer border
• Subclavius muscle: arises from the distal shaft and first costal cartilage
• First digitation of the serratus anterior muscle
• Parietal pleura: from the inner border
• Costoclavicular ligament: anterior to the groove for the subclavian vein

Palpation

The first rib is often noted as the most difficult rib to palpate. To palpate the first rib, find the superior border of the upper trapezius muscle and then drop off it anteriorly and direct your palpatory pressure inferiorly against the first rib. Asking a patient to take in a deep breath will elevate the first rib up against your palpating fingers and make palpation easier

Examination

First Rib Assessment on hypomobility in Supine:

Assessing Rib Mobility - Lindgren's Test:

Pathology/Injury

The first rib, in particular is involved in thoracic outlet syndrome and Pancoast tumour.

Thoracic Outlet Syndrome

The term ‘thoracic outlet syndrome’ describes compression of the neurovascular structures as they exit through the thoracic outlet (cervicothoracobrachial region). The thoracic outlet is marked by the anterior scalene muscle anteriorly, the middle scalene posteriorly, and the first rib inferiorly. The term ‘TOS’ does not specify the structure being compressed. TOS affects approximately 8% of the population and is 3-4 times as frequent In woman as in men between the age of 20 and 50 years. Females have less-developed muscles, a greater tendency for drooping shoulders owing to additional breast tissue, a narrowed thoracic outlet and an anatomical lower sternum, these factors change the angle between the scalene muscles and consequently cause a higher prevalence in women. Signs and symptoms of thoracic outlet syndrome vary from patient to patient due to the location of nerve and/or vessel involvement. Symptoms range from mild pain and sensory changes to limb threatening complications in severe cases.

Pancoast tumour

Or otherwise known as superior sulcus tumour, refers to a relatively uncommon situation where a primary bronchogenic carcinoma arises in the lung apex at the superior pulmonary sulcus and invades the surrounding soft tissues. Although classically superior sulcus tumours present with Pancoast syndrome, this is only the case in approximately 25% of cases. The missing element is usually Horner syndrome. The most common symptoms at presentation are chest and/or shoulder pain, with arm pain being also common. Weight loss is frequently present.

The first rib os also affect by pathology common to all ribs;

• infection, e.g. septic arthritis, osteomyelitis
• malignancy, e.g. chondrosarcoma, enchondroma, metastases
• trauma, e.g. fracture
  • first rib fractures are often associated with clavicle fractures or damage to adjacent neurovascular structures