Original Editor - Adam Vallely Farrell
The first rib is the most superior of the twelve ribs. It is an atypical rib and is an important anatomical landmark. It is one of the 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 then 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. The remaining ribs are typical.
Anatomy. The shaft is indented laterally, the groove for the subclavian artery, which contains the lowest brachial plexus trunk as well as the subclavian artery. Anterior to the scalene tubercle is another groove for the subclavian vein. There is no costal groove on its inferior surface. It has two tubercles:
- transverse tubercle: posterior and lateral to the neck; bears an articular facet for the transverse process of T1
- scalene tubercle: anteriorly between the grooves for the subclavian artery and vein; anterior scalene muscle inserts here
- it is also known as the Lisfranc tubercle, described by Lisfranc in 1815
Arterial blood supply arises from the internal thoracic and superior intercostal arteries. 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.
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 thoracic spinal nerves from T1 to T11. 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.
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
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
First Rib Assessment on hypomobility in Supine:
Assessing Rib Mobility - Lindgren's Test:
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.
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
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- First Rib Palpation Available from: https://www.youtube.com/watch?v=zwDO_VXOItM
- Assessment of Rib Mobility - Lindgren's Test Available from: https://www.youtube.com/watch?v=PrDZD1erucI
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