Thorax Osteology

Contents Overview Sternum Ribs Clavicle Thoracic Vertebrae

Overview Thorax is region of body contained within ribcage bony thoracic wall, the sternum helps protect the internal thoracic viscera – such as the heart, lungs and oesophagus

Overview Superior thoracic aperture Manubrium Ribs 1 Body of T1 vertebrae Inferior thoracic aperture Costal margin Ribs 11 and 12 Xiphoid Process Body of T12 vertebrae

Sternum Split into 3 parts

Sternum Manubrium Trapezoid shape, superior to sternum Articulation point for: Clavicle Rib 1 Half of rib 2 Jugular notch (T2) Sternal angle (T4/5) - These fossae articulate with the medial ends of the clavicles, forming the sternoclavicular joints. - On the lateral edges of the manubrium, there is a facet (cartilage lined depression in the bone), for articulation with the costal cartilage of the 1st rib, and a demifacet (half-facet) for articulation with part of the costal cartilage of the 2nd rib. - The sternal angle is commonly used as an aid to count ribs, as it marks the level of the 2nd costal cartilage and same level as aortic arch and carina (bifurication of trachea)

Sternum Body ‘’Chest Bone’’ Articulation with costal cartilages of ribs 3-6 The lateral edges of the body are marked by numerous articular facets (cartilage lined depressions in the bone). These articular facets articulate with the costal cartilages of ribs 3-6. There are smaller facets for articulation with parts of the second and seventh ribs – known as demifacets

Sternum Xiphoid Process Inferior to the body of sternum Found at T10 Marks central tendon of diaphragm, inferior border of heart and superior border of liver The xiphoid process is largely cartilaginous in structure, and completely ossifies late in life – around the age of 40 Xiphesternal joint at T9

Ribs Form the protective cage of the thorax 12 ribs Typical or atypical True, false or floating As part of the bony thorax, the ribs protect the internal thoracic organs. They also have a role in breathing – during chest expansion the ribcage moves to permit lung inflation Atypical – features not typical with other rribs

Ribs True Ribs 1-7 (attach to sternum via costal cartilage) False Ribs 8-10 (attach indirectly to sternum via costal cartilage of superior rib) Floating Ribs 11 & 12 (not attached to sternum)

Typical Ribs Ribs 3-9 Consists of head, neck and body Tubercle Angle Costal Groove Angle Crest - One facet articulates with the numerically corresponding vertebrae, and the other articulates with the vertebrae above - groove for the neurovascular supply of the thorax, protecting the vessels and nerves from damage - The smooth part of the tubercle is the articulates with transverse process of corresponding vertebrae. - The rough part of the tubercle is for attachment of the costotransverse ligament. - Costochondral joint attaches the rib to the costal cartilages.

Atypical Ribs Rib 1 Shorter Only one articular facet (T1) Grooves for SCA/SCV Tubercle for anterior scalene Rib 2 Thinner and longer than rib 1 Rough surface where posterior scalene attaches

Atypical Ribs Rib 10 Only one facet on head Rib 11 & 12 No neck

Clavicle ‘’Collar Bone’’ ‘S’ shaped Extends from manubrium to scapula 2 ends – acromial and sterna Midclavicular line Forms part of pectoral girdle Subclavian groove for attachment of subclavius muscle Attach the upper limb to the trunk Transmits forces from the limb to the axial skeleton The pectoral girdle is made of the clavicle and the scapula. It helps fix and hold the 1st rib in place so that the rest of the rib cage can expand and compress when taking a breath.

Thoracic Vertebrae 12 thoracic vertebrae forming thoracic spine Heart shaped Circular vertebral foramen L-P rule: Lamina are Posterior Pedicles are Lateral Laminae form the posterior walls of the vertebral foramen and connect the transverse process to spinous process. Pedicles form the lateral walls of the vertebral foramen and connect the body to the transverse process.

Thoracic Vertebrae 12 thoracic vertebrae forming thoracic spine Heart shaped Circular vertebral foramen L-P rule: Lamina are Posterior Pedicles are Lateral Ribs articulate with same level TV but also with superior one too Bilateral facets for ribs characteristic of thoracic Costal facets on T1-10 only

Clinical Relevance Flail Chest Rib breaks in two places Causes detachment from chest Prevents proper ventilation During inhalation, broken rib moves inwards Prevents proper ventilation thus oxygenation of blood Vice versa

Quiz What is the arrow pointing to? Xiphoid process What vertebral level does it sit? T10 What articulates with the manubrium? Clavicle, and costal cartilage of Rib 1 & 2

Summary Had a look into the bones that make up the thorax – Sternum, ribs, clavicle and thoracic vertebra Also looked at some clinical relevance towards the osteology of the thorax