THORACIC CAGE

THORACIC CAGEDr. Aunum Iqbal

COMPONENTS OF THORACIC CAGE:

SternumManubrium, Body (Gladiolus), Xiphoid process

Ribs7 True Ribs5 False Ribs (including 2 floating ribs)

Clavicle PectoralScapula girdle

12 Thoracic Vertebrae (T1 - T12)

Thoracic CageIt forms a conical enclosure for the lungs and heart and provides attachment for the pectoral girdle and upper limb.It has a broad base and a narrower superior apex; it is rhythmically expanded by the respiratory muscles to create a vacuum that draws air into the lungs.The inferior border of the thoracic cage is formed by a downward arc of the ribs called the costal margin.The ribs protect the thoracic organs and spleen, most of the liver, and to some extent the kidneys.

Sternum/Breast boneFlat bone, with 3 parts:

Manubrium sterniBody/GladiolusXiphoid process

PARTS OF STERNUM:Manubrium sterniJugular/suprasternal notchArticulates with Clavicles and Ribs 1 and 2Lies opposite to T3 and T4 vertebraeManubriosternal joint inferiorly called Sternal Angle/Angle of Louis opposite articulation with 2nd rib at the level of intervertbral disc between T4 and T5 vertebrae(imp. for counting the ribs)

PARTS OF STERNUM:

2. Body/GladiolusArticulates with Ribs 2-7Xiphisternal joint inferiorly- opposite to T9 vertebra

3. Xiphoid processCartilaginous - calcifies through timeAllows attachment of musclesTip of xiphoid at level of T10

Clinical AnatomyBone marrow biopsy (to take sample of bone marrow)

Median sternotomy (Sternum is split in half, longitudinally to gain access to thoracic organs for surgery)

Sternocostal joints

RibsTypical Ribs 2-7HeadNeckTubercleAngleShaftSubcostal groove

Atypical Ribs 1, 8 -10Rib 1 - short, flat and supports Subclavian vessels Ribs 1, 10-12 - articulate with only 1 vertebra Ribs 11 and 12 floating ribs do not articulate with Transverse processes of Vertebrae or Sternum

Typical ribs:1 7 pairs of ribs are attached anteriorly to the sternum by their costal cartilages.

Atypical ribs:8th, 9th and 10th pairs of ribs are attached anteriorly to each other and to the 7th rib by means of their costal cartilages and small synovial joints.

Floating ribs:The 11th and 12th pairs have no anterior attachment. They are embedded in the abdominal muscles.

Typical Ribs (2 -7)Long, twisted, flat boneThe anterior end of each rib is attached to the corresponding costal cartilage A rib has ahead, neck, tubercle, shaft, andangle Head located posteriorly -has 2 facets for articulation one for the numerically corresponding vertebral body and the other for the vertebral body immediately above it. Neckis a constricted portion - between the head and the tubercle. TheTubercleis a prominence on outer surface of the rib - at the junction of the neck with the shaft. It has a facet for articulation with the transverse process of the numerically corresponding vertebra. The Shaft is thin, flat and twisted on its long axis.It has a rounded, smooth superior border and a sharp, thin inferior border which hascostal groove (it accommodates the intercostal vessels and nerve (VAN ) The angle is where the shaft of the rib bends sharply forward.

Atypical Rib (1st Rib)The first rib has a close relationship to the lower nerves of the Brachial plexus, Subclavian artery and vein

This rib is small and flattened from above downward

Scalenus anterior muscle is attached to its upper surface and inner border

Anterior to the attachment of Scalenus anterior, the Subclavian vein crosses the rib

Posterior to the attachment of Scalenus anterior, the Subclavian artery and the lower trunk of the Brachial plexus cross the rib and lie in contact with the bone

Clinical AnatomyFracture of 1st rib may cause:Injury to lower trunk of Brachial plexus: Klumpkes paralysisInjury to Subclavian vessels: Hemorrhage/Ischemia

Thoracic outlet syndrome: Compression of Subclavian vessels/Brachial plexus between 1st Rib and Clavicle Klumpkes paralysis and ischemia.

JOINTS

JOINTS OF STERNUM1. MANUBRIOSTERNAL JOINT:cartilaginous joint, symphysisbetween Manubrium and body of Sternum

2. XIPHISTERNAL JOINTcartilaginous jointbetween Xiphoid process and body of SternumThe Xiphoid process usually fuses with the body of the Sternum during middle age

JOINTS OF RIBS1. COSTOVERTEBRAL JOINTS:2 joints between heads of the Ribs and bodies of Vertebrae (corresponding and upper)- Synovial joints1st, 10th, 11th and 12th rib has 1 synovial joint with the corresponding vertebra, the rest have 2 each; one for the corresponding vertebra and the other for the vertebra above it1 joint between tubercle of Ribs and transverse process of Vertebra (corresponding) - Synovial joint (1st-10th Rib)Intra articular ligament connects head of Rib to the intervertebral disc

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JOINTS OF RIBS2. COSTOCHONDRAL JOINTS:Joints of the Ribs with costal cartilagesCartilaginous joints

3. STERNOCOSTAL JOINTS:Joints between Sternum and costal cartilages1st : Cartilaginous joint2nd 10th : Synovial joints= 2nd-7th costal cartilages with Sternum8th-10th costal cartilages with each other(11th and 12th costal cartilages are embedded in muscles)

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MOVEMENTSCartilaginous joints are immobile (thus 1st rib and all costochondral joints do not move during respiration)

Synovial joints are slightly mobile (due to movements in both the joints between head, tubercle and vertebrae, necks of Ribs rotate along their axis, helping in raising and lowering of ribs during respiration)

Cervical Rib (Accessory Rib)Occurs in 0.5% populationThere is an extra pair of ribs just above the 1st ribThey arise from the transverse process of C7 vertebraeAnteriorly, they may be attached to 1st Rib or may be freeClinical Anatomy: Cervical Rib may compress Brachial plexus/Subclavian artery; causing Klumpkes paralysis/Ischemia