SH Thorax anatomy

Costovertebral joints

synovial plane joint between the heads of ribs and the superior/inferior costocapitular facets and intervening intervertebral disk A double synovial compartment, one for each demifacet. The compartments are separated by an intra-articular ligament which extends from the crest of the head of the rib to the intervertebral disk. Radiate ligaments also support this joint, attaching the head of the rib to the adjacent vertebral bodies.

Costotransverse joints

A synovial plane joint between the costotubercular facet of the transverse process and the articular facet of the tubercle of the corresponding rib. Strengthened by costotransverse ligaments.

Pectus excavatum

sunken sternum and adjacent cartilages An anomaly where the sternum is pressed inwards, widening the cardic shadow on X-ray.

Diaphragm innervation

Phrenic nerve c345 keeps the diaphragm alive Motor to diaphragm, sensory to central diaphragm, pericardium and mediastinal pleura

Structure of the diaphragm

Composed of a right dome, left dome and non-muscular central tendon where the IVC passes through The oesophagus and aorta pass behind the central tendon Left and right crura Medial and lateral arcuate ligaments on either side, and a median arcuate ligament which goes over the aorta

Diaphragm paralysis

Damage to phrenic nerve, can result from surgery Results in usually unilateral injury Diaphragm may be displaced on CXR, e.g. higher than normal Patient may present with SOB

Variations in ribs

12 paired ribs Rib 3-9 are typical, others are atypical. Ribs 1-7 are true ribs and directly connected to the sternum by their costal cartilages. Ribs 8-10 are false ribs and indirectly are connected to sternum by the costal cartilages of ribs above them. Ribs 11-12 are not connecting to the sternum and are called floating ribs. The costal margin is formed by ribs 7-10 and their associated costal cartilages.

Accessing the thorax

Aim needle above the rib to avoid damaging the main intercostal VAN bundles since they tend to run along the lower border of ribs

Diaphragm boundaries

Anterior - the back of the xiphoid process Posterior - lumbar vertebra via crura and arcuate ligaments Lateral - lower 6 costal cartilages

Blood drainage of the thorax

Follows arteries 1st posterior intercostal veins drain into the brachiocephalic trunk on both sides Right side - posterior intercostal veins to the azygous vein Left side - posterior intercostal veins into the brachiocephalic trunk and hemiazygous or azygous if hemiazygous veins are not present Anterior intercostal veins drain into the internal thoracic and musculophrenic veins

Diaphragm - blood supply

Has its own blood supply The phrenic arteries and more

Atypical rib 10-12

Like T1, only have one facet on their heads and articulates with a single vertebra Ribs 11-12 are short and have no tubercles or necks, grooves, or angles.

Atypical rib 2

Like rib 1, but is thinner and longer than rib 1. Head has 2 facets for articulation with bodies of T1 and T2. Has a rough tuberosity on its superior surface for the serratus anterior, for which part of the muscle originates

Innervation of the thoracic wall

Mainly T2-T12 Segmental inntervation Fibres of the anterior rami of each spinal nerve innervates their respective dermatomes and myotomes. T10 includes the umbilicus T4 includes the nipple There is substantial overlap in between segments

Features of the sternum

Manubrium - has a jugular notch superiorly, 2 clavicular facets for articulation with the clavicle and facets for the 1st and (partially) 2nd costal cartilages. Body - formed from fusion of 4 sternebrae and may have 3 lines of fusion. On its lateral border are 4 costal facets for articulation with the 3-6th costal cartilages. The inferior angle has a sternal angle which, with the xiphoid process, receives the 7th costal cartilage. Xiphoid process jointed to the body by the xiphisternal joint The sternum forms from segments. Joints are cartilaginous and springy. Ossification later in life can lead to bony fusion and rigidity. The sternal angle is the joint between the manubrium and the body. It creates a little ridge, is palpable and is an important landmark for T4/5. It is where the 2nd costal cartilge articulates with the sternum.

Flail chest

Occurs with car collisions fracture of two or more adjacent ribs in two or more places that allows for free movement of the fractured segment When diaphragm contracts and creates negative pressure for inhalation, the broken segments will be drawn in, and then pushed out when exhaling. A paradoxical movement.

Blood supply of the thorax

Paired posterior intercostal arteries - 1st and 2nd from superior intercostal trunk - 3rd - 11th from aorta directly Paired anterior intercostal arteries - 6 from internal thoracic A - 7-9th from musculophrenic A

Typical ribs

Ribs 3-9 Has a shaft with anterior and posterior ends Anterior or sternal end has a pit for the costal cartilage's lateral head The posterior or vertebral end has a head with 2 articular facets separated by an interarticular crest. The lower, larger facet articulates with the superior costocapitular demifacets of the corresponding vertebra, and the upper, smaller facet articulates with the inferior costocapitular demifacets of the supradjacent vertebra. There is a neck, which is flattened and behind the head Just past the neck is a tubercle, posterior and external. It has an articular area for the costotubercular facet on the corresponding transverse process, and a rough non-articular area for attachment of ligaments. There is a costal angle past the tubercle, which is a sharp change in direction of the shaft. The shaft has a external convexity and is grooved internally near its lower border, the costal groove. This protects the intercostal VANs (sup-inf).

Structures that pass through the diaphragm

T8 IVC T10 Oesophagus T12 Aorta Also the phrenic nerves, splanchnic nerves, vagus nerves, and thoracic duct

Surface anatomy correlations: T4/T5 intervertebral disc (7)

Sternal angle (2nd costal cartilage) Inferior border of superior mediastinum End of aortic arch Point of entry of SVC into pericardium Azygous vein entry into SVC Bifurcation of trachea Superior limit of the pulmonary trunk *** these correlations vary depending on gender, postural position (gravity), body composition. The correlations above are obtained from CTs in a supine position.

Atypical thoracic vertebrae

T1, T9-T12 T1 has a single, circular costocapitular facet (as opposed to 2 demifacets), an inferior demifacet (?) and a thick, prominent horizontal spinous process T9-T12 have single costocapitular facets T11-T12 have no costotubercular facets

Variations in thoracic vertebra

T1-T4 - some features of C vertebrae T5-T8 - consistent T9-T12 - some features of L vertebrae T1, T9-T12 are considered atypical vertebrae

Lymphatics of the thoracic wall and diaphragm

TBC

Atypical rib 1

The broadest, shortest and most sharply curved of the 7 true ribs. The head is round with a single facet for articulation with the T1 vertebra only The tubercle is flat and large and articulates with the T1 transverse process. Sits at the thoracic inlet, so there are 2 grooves on its superior surface for the subclavian artery ( laterally) and vein (medially), separated by a palpable scalene tubercle for attachment of the scalenus anterior muscle. There are other points for the attachment of muscles and ligaments.

Intercostal muscles

The external intercostals do not occupy the anterior intercostal space, replaced by a membrane Vice versa for internal intercostals which do not occupy the posterior space VAN travel between the internal and external intercostals Transversus thoracis muscles lies internal to the thoracic cage, behind the internal intercostals

Components & boundaries of the thorax

The thoracic cavity forms a truncated cone with an elliptical cross section 12 thoracic vertebrae 12 ribs and their hyaline costal cartilages The sternum Superior margin is the thoracic inlet, composed of 1st thoracic vertebra posteriorly, 1st rib and costal cartilage laterally, and the manubrium anteriorly. Inferior margin is the thoracic outlet composed of 12th thoracic vertebra posteriorly, 12th rib and the costal margin (7-12 costal cartilages) laterally, the xiphisternal joint anteriorly and closed off by the diaphragm inferiorly

Features of typical thoracic vertebrae

Typical vertebrae (2-8): - 2 demifacets on the body, superior articulates with the head of the corresponding rib and the inferior with the rib below. - small vertebral foramen - heart-shaped body, forming the anterior part of the vertebral foramen - vertebral arch, forming the posterior part of the vertebral foramen, with 2 short, thick laminae that overlap from above downwards - superior articular processes on the laminae, which articulate with the inferior articular processes of above vertebrae - spinous processes which projects posteriorly and inferiorly between the laminae - transverse processes with anteriorly facing oval costotubercular facets for articulation with the tubercles of the corresponding ribs

Features of CXRs

X-ray beams are absorbed by hard tissues and not by soft tissues, like skin and organs. As a result, when the beams hit the detector, hard tissues like bones are white while soft tissues are black. Costal cartilages are not visible Lung fields are black but vascular features can be seen The diaphragm is generally uneven - right side is higher than left due to liver Gastric bubble - air collecting at fundus of stomach A bubble at the hilum may indicate a collapsed lung Posterior-anterior xrays are preferred. The cardiac shadow may appear larger in an AP x-ray.

Chondrosternal joints

between the costal cartilages and and the lateral facets of the sternum

Costochondral joints

joints between each bony rib and its respective costal cartilage