Anatomy of Thoracic Cage PDF

ANATOMY OF THORACIC WALL STRUCTURE ASSOCIATED LAB/ LECTURE Made up of − sternum − 12 pairs of ribs − 12 thoracic vertebrae NB: Sternum – manubrium, body, xiphoid process 12 pairs of ribs – − 1 – 7 are true ribs (vertebrosternal ribs) − 8 – 10 are fa...

ANATOMY OF THORACIC WALL STRUCTURE ASSOCIATED LAB/ LECTURE Made up of − sternum − 12 pairs of ribs − 12 thoracic vertebrae NB: Sternum – manubrium, body, xiphoid process 12 pairs of ribs – − 1 – 7 are true ribs (vertebrosternal ribs) − 8 – 10 are false ribs (vertebrochondral ribs) − 11 – 12 are floating ribs (vertebral ribs) FUNCTIONS OF THORACIC CAGE - Protects the upper abdominal viscera, heart, lungs, thymus, nerves and blood vessels - Serves for the attachment of muscles involved in respiration - Movements of pectoral girdle and upper limb THORACIC INLET & OUTLET - STERNUM STERNAL ANGLE - Sternal angle can be felt as a transverse ridge on sternum around 5cm below the suprasternal notch - Second costal cartilage articulates, on either side with the sternum at this level, hence this level is used for counting the ribs below - Sternal angle lies at the level of intervertebral disc between T4 and T5 - Horizontal plane passing through this level separates superior mediastinum from inferior mediastinum - Ascending aorta ends, arch aorta begins and ends, and descending aorta begins at this level - Trachea bifurcates into right and left principal bronchi at this level - Pulmonary trunk divides into right and left pulmonary arteries at this level - Azygos vein arches over the root of right lung to open into the superior vena cava ATTACHMENT OF STERNUM OSSIFICATION OF STERNUM THORACIC VERTEBRAE - Presence of articular facets on each side of the body and on front of transverse process for articulation with the ribs - Upper larger costal facet articulates with the head of numerically corresponding rib and lower costal facet with the rib below - Body is heart shaped, vertebral foramen is circular - Spinous process is long, slender and directed downwards - Pedicle is attached to the upper part of the body, thus making the inferior vertebral notch deeper - T2-T8 are typical - T1, T9-T12 are atypical JOINTS OF THE VERTEBRAL COLUMN All the joints from C2 – S1 articulate by: - Secondary cartilaginous joint (symphysis) – between adjacent bodies of vertebrae - Synovial joints – between their articular processes - Fibrous joints – between their laminae, transverse process and spinous process - Interlaminar or Zygapophysial joints – plane variety of synovial joint Nerve supply – branch from dorsal rami of spinal nerve at the level of the joint INTERVERTEBRAL JOINTS - Joints btw the adjacent vertebral bodies are symphysis or secondary cartilaginous joint - The vertebral bodies are connected by anterior and posterior longitudinal ligaments - Between the bodies is the intervertebral disc, which is made up of outer annulus fibrosus and inner nucleus pulposus LIGAMENTS OF THE VERTEBRAL COLUMN - Ligamentum nuchae - Anterior and posterior longitudinal ligament - Ligamentum flava - Interspinous ligament - Supraspinous ligament - Inter-transverse ligament RIBS (COSTAE) - Flat, ribbon-like, elastic bony arches which extend from thoracic vertebrae posteriorly to the lateral border of the sternum anteriorly Normally 12 pairs of ribs Classification of ribs: 1. According to features I. Typical ribs: 3rd – 9th; typical ribs have same general features (CAT : Curved, Angulated and Twisted) II. Atypical ribs: 1st, 2nd, 10th, 11th, 12th ; have special features, therefore differ from typical ribs and other atypical ribs 2. According to articulation w/the sternum I. True ribs: 1st – 7th ribs; articulate with the sternum anteriorly II. False Ribs: 8th – 12th ribs; do not articulate directly with the sternum anteriorly 3. According to articulation I. Vertebrosternal ribs: 1st – 7th ribs II. Vertebrochondral ribs: 8th – 10th ribs III. Vertebral Ribs or Floating Ribs – 11th & 12th ribs 4. 3rd – 9th ribs are typical FEATURES OF TYPICAL RIBS: - Anterior end, posterior end and shaft - Anterior end: articulates with the corresponding costal cartilage to form costochondral joint – primary cartilaginous variety of joint - Posterior end presents head, neck and tubercle Head Presents two articular demi-facets (upper and lower), which are separated by intra- articular crest. - The upper smaller demi-facet articulates with the lower demi-facet present on the body of the thoracic vertebra above - The lower larger demi-facet articulates with the body of the numerally corresponding thoracic vertebra (with the upper demi-facet present on the body) - The intra-articular crest lies opposite the intervertebral disc Neck - Lies in front of the transverse process of the corresponding vertebra - It shows sharp crest like superior border and rounded inferior border, and anterior & rough posterior surface Tubercle - It is situated on the outer surface of the rib at the junction of neck and shaft It is divided into: - Medial articular part – presents a small facet for the transverse process of corresponding vertebra - Lateral non-articular part is rough for attachment of ligaments Shaft It is thin and flat and it presents: - Two borders – upper and lower - Two surfaces – outer and inner - Two angles – posterior (5 cm in front of the tubercle) and anterior (2cm behind the anterior end) I. Upper border - presents outer lip (attachment of external intercostal), inner lip (attachment of innermost intercostal) and intermediate area (attachment of internal intercostal) II. Lower border - is sharp and forms the lower border of the costal groove and gives attachment to external intercostal muscle Outer Surface is smooth and presents two angles posterior and anterior I. Posterior angle- (angle of the rib – weak point) is marked by an oblique ridge (5cm in front of tubercle). II. Anterior angle- is marked by an indistinct oblique line (2cm behind the anterior end) Inner Surface- presents a costal groove near its lower border, which lodges the intercostal vein, artery and nerve (VAN), from above downward. NB: The internal intercostal is attached to the floor of the groove, the innermost intercostal is attached to the upper lip of the costal groove and external intercostal is attached to its lower border FEATURES OF ATYPICAL RIBS: First Rib: FEATURES OF ATYPICAL RIBS: Second Rib: FEATURES OF ATYPICAL RIBS: 10th rib: - Single articular facet on its head, which articulates with the body of corresponding thoracic vertebra 11th rib: - It has single large facet on its head for the 11th vertebra - It has no neck or tubercle - Its anterior end is pointed and tipped with cartilage - It has slight angle and shallow costal groove 12th rib: - It has single large facet on its head for the 12th vertebra - It has no neck or tubercle - It has no angle or costal groove - Much shorter than 11 rib JOINTS OF THORACIC CAGE: - Sternoclavicular joint: Plane synovial joint - Manubrio-sternal joint: Secondary cartilaginous joint (symphysis) - Xiphisternal joint: Primary cartilaginous joint (synchondrosis) - Costovertebral joints: Plane synovial joint - Costotransverse joints: Plane synovial joint - Costochondral joints: Primary cartilaginous joint (synchondrosis) - Chondro-sternal joint: First chondro- sternal joint is primary cartilaginous and 2nd – 7th chondro-sternal joints are plane synovial joints - Interchondral joints: 5th to 9th costal cartilages articulate with one another to form synovial joint CERVICAL RIB: - costal element of C7 vertebrae may elongate to form a cervical rib - Present in 5% of individuals. Frequently present on the right side. NB: It may compress the lower trunk of brachial plexus and subclavian artery; producing pain along the medial side of forearm and hand; disturbance in the circulation of the upper limb (thoracic inlet syndrome or cervical rib syndrome) LUMBAR RIB (Gorilla Rib): - Develops from costal element of L1 vertebra. - Its incidence is more common than the cervical rib, but remains undiagnosed - usually does not cause any symptoms. - It may be confused for fracture of transverse process of L1 vertebra. FRACTURE OF RIB: - The rib commonly fractures at its angle as it is the weakest point. - Usually, the middle ribs are involved in the fracture. FLAIL CHEST (Stove-in-chest) - When ribs are fractured at two sites (anteriorly as well as at the angle), the flail chest occurs. CLINICAL CORRELATIONS 1. Sternal Puncture: - Manubrium sterni is the preferred site for bone marrow aspiration (for hematological examination) because it is subcutaneous and readily accessible. - A thick needle is inserted into the upper part of manubrium to avoid injury to arch of aorta, which lies behind the lower part. - Sternal puncture is not advisable in children because in them the sternum is very thin. - Mid-sternotomy: To gain access for surgical operations on heart and great blood vessels the sternum is often divided in the median plane. 2. Funnel Chest (pectus excavatum) - In which chest is compressed anteroposteriorly and sternum is pushed backward by the overgrowth of the ribs and may compress the heart 3. Pigeon chest (pectus carinatum): In which chest is compressed from side to side and sternum projects forward and downward like a keel of a boat 4. Sternal fracture: - common in automobile accidents; backward displacement of fractured fragments may damage aorta, heart or liver and cause severe bleeding which may prove fatal. 5. Sternal foramen or cleft sternum - failure of sternebrae to fuse in the midline, as a result defect occurs in the body of the  sternum in the form of sternal foramen or cleft sternum. The cleft sternum is often associated with ectopia cordis 6. Cardiopulmonary Resuscitation (CPR) - chest compressions and rescue breaths to victims of a cardiac arrest. - Chest compressions are delivered in the center of the chest over the sternum. - CPR works by keeping oxygenated blood flowing around the body in order to keep vital organs (such as the heart and brain) alive. - Chest compressions are a vital part of CPR, the rescuer should provide 100 – 120 chest compressions a minute at a depth of 5 – 6cm. - It is common for ribs to be broken during CPR. Prevalence of rib fractures in adult victims who received CPR was over 80%. In rare cases the sternum may also gets fractured (age related).