Upper Limb Anatomy: Bones and Joints

• The upper limb is specialized for mobility and manipulation, while the thorax provides protection for vital organs and plays a crucial role in respiration.

Upper Limb

• The upper limb consists of the shoulder, arm, forearm, and hand.
• Bones of the upper limb include the clavicle, scapula, humerus, radius, ulna, carpals, metacarpals, and phalanges.
• Joints of the upper limb include the sternoclavicular, acromioclavicular, glenohumeral (shoulder), elbow, radioulnar (proximal and distal), wrist, carpometacarpal, metacarpophalangeal, and interphalangeal joints.

Shoulder Region

• The pectoral girdle is formed by the clavicle and scapula, connecting the upper limb to the axial skeleton.
• The clavicle articulates with the sternum at the sternoclavicular joint and with the acromion of the scapula at the acromioclavicular joint.
• The scapula is a flat, triangular bone that lies on the posterior aspect of the thorax, overlying ribs 2-7.
• The glenoid cavity of the scapula articulates with the head of the humerus to form the glenohumeral joint (shoulder joint).
• Muscles of the shoulder region include the deltoid, trapezius, latissimus dorsi, rhomboids, levator scapulae, and serratus anterior.
• The rotator cuff muscles (supraspinatus, infraspinatus, teres minor, and subscapularis) stabilize the shoulder joint and allow for a wide range of movements.

Arm

• The arm extends from the shoulder to the elbow.
• The humerus is the bone of the arm, articulating with the scapula at the shoulder joint and with the radius and ulna at the elbow joint.
• Muscles of the anterior compartment of the arm (biceps brachii, brachialis, coracobrachialis) primarily flex the elbow and/or shoulder.
• Muscles of the posterior compartment of the arm (triceps brachii, anconeus) primarily extend the elbow.
• The brachial artery is the main artery of the arm, branching into the radial and ulnar arteries in the forearm.
• Major nerves of the arm include the musculocutaneous, median, ulnar, and radial nerves.

Forearm

• The forearm extends from the elbow to the wrist.
• The radius and ulna are the two bones of the forearm.
• The radius is located on the lateral (thumb) side of the forearm, while the ulna is on the medial (pinky) side.
• The proximal radioulnar joint allows for pronation and supination of the forearm.
• Muscles of the anterior compartment of the forearm (wrist flexors, pronators) generally originate from the medial epicondyle of the humerus.
• Muscles of the posterior compartment of the forearm (wrist extensors, supinators) generally originate from the lateral epicondyle of the humerus.
• Key muscles include flexor carpi ulnaris, palmaris longus, flexor carpi ulnaris, extensor carpi radialis longus and brevis, extensor carpi ulnaris.
• The radial and ulnar arteries supply blood to the forearm and hand.
• The median, ulnar, and radial nerves provide innervation to the forearm and hand.

Hand

• The hand consists of the wrist, palm, and fingers.
• The wrist is composed of eight carpal bones arranged in two rows.
• The palm contains five metacarpal bones.
• Each finger (except the thumb) has three phalanges (proximal, middle, and distal), while the thumb has two phalanges (proximal and distal).
• Intrinsic muscles of the hand (thenar, hypothenar, and interosseous muscles) control fine motor movements of the fingers.
• The hand is supplied by branches of the radial and ulnar arteries, forming palmar arches.
• The median and ulnar nerves provide sensory and motor innervation to the hand.

Thorax

• The thorax is the region of the body between the neck and the abdomen.
• It provides bony protection for the heart, lungs, and other vital organs.
• The thoracic skeleton includes the sternum, ribs, costal cartilages, and thoracic vertebrae.
• The thoracic cavity contains the pleural cavities (containing the lungs), the mediastinum, and the superior thoracic aperture (thoracic inlet) and inferior thoracic aperture (thoracic outlet).

Thoracic Wall

• The thoracic wall is formed by the thoracic skeleton and associated muscles.
• The sternum consists of the manubrium, body, and xiphoid process.
• There are 12 pairs of ribs: true ribs (1-7) attach directly to the sternum via costal cartilages, false ribs (8-10) attach indirectly to the sternum via the costal cartilage of the rib above, and floating ribs (11-12) do not attach to the sternum.
• Intercostal muscles (external, internal, and innermost) occupy the spaces between the ribs and assist with respiration.
• The diaphragm is a large, dome-shaped muscle that separates the thoracic cavity from the abdominal cavity and is the primary muscle of respiration.
• The thoracic wall is supplied by intercostal arteries and veins, which run along the costal grooves of the ribs.
• Intercostal nerves (ventral rami of thoracic spinal nerves) provide sensory and motor innervation to the thoracic wall.

Thoracic Cavity and Mediastinum

• The pleural cavities are potential spaces between the parietal pleura (lining the thoracic wall) and the visceral pleura (covering the lungs).
• The mediastinum is the central compartment of the thoracic cavity, containing the heart, great vessels, trachea, esophagus, thymus gland, and lymph nodes.
• The superior mediastinum lies above the pericardium and contains the thymus, great vessels (aortic arch, superior vena cava), trachea, esophagus, and thoracic duct.
• The inferior mediastinum lies below the pericardium and is divided into the anterior, middle, and posterior mediastinum.
• The anterior mediastinum contains the thymus gland, fat, and lymph nodes.
• The middle mediastinum contains the heart, pericardium, and great vessels (ascending aorta, pulmonary trunk).
• The posterior mediastinum contains the esophagus, descending aorta, azygos and hemiazygos veins, thoracic duct, and sympathetic trunks.

Lungs and Pleurae

• The lungs are the primary organs of respiration, responsible for gas exchange.
• The right lung has three lobes (superior, middle, and inferior), while the left lung has two lobes (superior and inferior).
• The hilum of each lung is the point where the bronchi, pulmonary vessels, and nerves enter and exit the lung.
• The trachea bifurcates into the right and left main bronchi, which enter the lungs and further divide into lobar and segmental bronchi.
• The bronchioles are smaller branches of the bronchi that lead to the alveoli, where gas exchange occurs.
• The pulmonary arteries carry deoxygenated blood from the heart to the lungs, while the pulmonary veins carry oxygenated blood from the lungs to the heart.
• The bronchial arteries supply oxygenated blood to the lung tissue.
• The pleurae are serous membranes that surround the lungs, providing lubrication and allowing the lungs to expand and contract during respiration.

Heart and Pericardium

• The heart is a muscular organ that pumps blood throughout the body.
• It is located in the middle mediastinum, surrounded by the pericardium.
• The pericardium is a double-layered sac that encloses the heart: the fibrous pericardium (outer layer) and the serous pericardium (inner layer).
• The serous pericardium is further divided into the parietal pericardium (lining the fibrous pericardium) and the visceral pericardium (epicardium), which adheres to the heart.
• The space between the parietal and visceral layers contains a thin film of serous fluid (pericardial fluid) that lubricates the surfaces, allowing the heart to move freely during contraction.
• The fibrous pericardium is the outer layer, made of dense connective tissue and protects the heart, anchors it within the mediastinum and prevents overfilling.
• The heart wall consists of three layers: epicardium, myocardium, and endocardium.
• The epicardium is the outer layer, also known as the visceral layer of the serous pericardium.
• The myocardium is the middle layer, composed of cardiac muscle responsible for the heart's pumping action.
• The endocardium is the inner layer, lining the heart chambers and covering the valves; it is made of a thin layer of endothelium and connective tissue.
• The heart has four chambers: two atria (right and left) and two ventricles (right and left).
• The right atrium receives deoxygenated blood from the superior vena cava, inferior vena cava, and coronary sinus.
• The right ventricle pumps deoxygenated blood to the lungs via the pulmonary trunk.
• The left atrium receives oxygenated blood from the pulmonary veins.
• The left ventricle pumps oxygenated blood to the body via the aorta.
• The atrioventricular valves (tricuspid valve on the right and mitral valve on the left) prevent backflow of blood from the ventricles into the atria.
• The semilunar valves (pulmonary valve and aortic valve) prevent backflow of blood from the pulmonary artery and aorta into the ventricles.
• The heart is supplied by the coronary arteries, which arise from the aorta.
• Cardiac veins drain deoxygenated blood from the heart muscle into the coronary sinus, which empties into the right atrium.
• The heart is innervated by the autonomic nervous system (sympathetic and parasympathetic fibers), which regulate heart rate and contractility.

Congenital Heart Diseases (CHDs)

• Congenital heart diseases are structural defects of the heart or great vessels present at birth.
• CHDs are the most common type of birth defect, affecting ~1% of live births.
• CHDs range in severity from simple defects requiring no treatment to complex, life-threatening malformations.

Etiology

• The etiology of CHDs is multifactorial.
• Genetic factors include chromosomal abnormalities such as Down syndrome (trisomy 21) and Turner syndrome, as well as single-gene mutations.
• Environmental factors include maternal infections such as rubella, maternal diabetes, and exposure to certain drugs or alcohol during pregnancy.
• In many cases, the specific cause is unknown.

Classification

• CHDs can be classified based on primary physiological abnormality.
  • Lesions causing a left-to-right shunt (atrial septal defect, ventricular septal defect, patent ductus arteriosus).
  • Lesions causing a right-to-left shunt (tetralogy of Fallot, transposition of the great arteries).
  • Lesions causing obstruction (pulmonary stenosis, aortic stenosis, coarctation of the aorta).
• CHDs can be classified based on the complexity of the defect as either simple or complex.

Common Congenital Heart Defects

Atrial Septal Defect (ASD)

• ASD is an opening in the interatrial septum, allowing blood to flow between the left and right atria.
• An ASD results in a left-to-right shunt, with oxygenated blood flowing from the left atrium to the right atrium.
• Most with ASDs are asymptomatic in childhood, but symptoms like dyspnea, fatigue, and palpitations can develop in adulthood.
• A large ASD can lead to pulmonary hypertension, right heart failure, and paradoxical embolism over time.

Ventricular Septal Defect (VSD)

• VSD is an opening in the interventricular septum, allowing flow between the left and right ventricles.
• A VSD results in a left-to-right shunt, with oxygenated blood flowing from the left ventricle to the right ventricle.
• Clinical presentation varies based on the defect's size.
• Small VSDs may be asymptomatic; large VSDs can cause heart failure, pulmonary hypertension, and failure to thrive.

Patent Ductus Arteriosus (PDA)

• The ductus arteriosus connects the pulmonary artery to the aorta during fetal development, bypassing the fetal lungs.
• After birth, the ductus arteriosus normally Closes within days.
• A PDA occurs when the ductus arteriosus fails to close, resulting in a left-to-right shunt between the aorta and the pulmonary artery.
• Premature infants have a higher risk of PDA.
• A PDA can lead to pulmonary hypertension, heart failure, and necrotizing enterocolitis.

Tetralogy of Fallot (TOF)

• TOF is characterized by four key features.
  • Ventricular septal defect (VSD).
  • Pulmonary stenosis (narrowing of the pulmonary valve and outflow tract).
  • Overriding aorta (positioned over the VSD, receiving blood from both ventricles).
  • Right ventricular hypertrophy (thickening of the right ventricle muscle).
• TOF results in a right-to-left shunt, with deoxygenated blood entering the systemic circulation.
• Infants with TOF typically present with cyanosis, especially during crying or feeding.
• Other symptoms include dyspnea, fatigue, and poor weight gain.
• Surgical repair is usually performed in infancy or early childhood.

Transposition of the Great Arteries (TGA)

• In TGA, the aorta arises from the right ventricle, and the pulmonary artery arises from the left ventricle.
• TGA results in two separate circulatory systems: deoxygenated blood circulates through the body, while oxygenated blood circulates through the lungs.
• TGA is life-threatening, requiring surgical correction in the first few weeks of life.

Coarctation of the Aorta

• Coarctation of the aorta is a narrowing of the aorta, typically near the ductus arteriosus.
• This restricts blood flow to the lower body, leading to hypertension in the upper extremities and hypotension in the lower extremities.
• Infants with severe coarctation may present with heart failure, while older children may be asymptomatic or have claudication.
• Treatment involves surgical repair or balloon angioplasty.

Pulmonary Stenosis (PS)

• Pulmonary stenosis is a narrowing of the pulmonary valve or artery, obstructing blood flow from the right ventricle to the lungs.
• This increases the workload of the right ventricle, leading to right ventricular hypertrophy.
• Severity ranges from mild (asymptomatic) to severe (cyanosis and right heart failure).
• Treatment varies based on severity; severe cases usually require balloon valvuloplasty or surgical repair.

Aortic Stenosis (AS)

• Aortic stenosis is a narrowing of the aortic valve, obstructing blood flow from the left ventricle to the aorta.
• This increases the workload of the left ventricle, potentially leading to left ventricular hypertrophy and heart failure.
• Treatment (valve replacement or balloon valvuloplasty) depends on the degree of obstruction.

Diagnosis

• Diagnosis of CHDs involves a combination of clinical evaluation and diagnostic testing.
• Physical examination includes listening for heart murmurs and assessing for cyanosis and edema.
• Electrocardiogram (ECG) records the electrical activity of the heart.
• Echocardiogram uses ultrasound to visualize the heart structure and function.
• Chest X-ray evaluates the size and shape of the heart and great vessels.
• Cardiac catheterization involves inserting a catheter into the heart to measure pressures and oxygen saturations; can also be used for interventions.

Treatment

• Treatment for CHDs varies depending on the type and severity of the defect.
• Some small defects may close spontaneously or require no treatment.
• Other defects may be managed with medications to control symptoms or prevent complications.
• Many CHDs require surgical repair or intervention.
  • Open-heart surgery to repair or replace valves, close defects, or reroute blood flow.
  • Catheter-based procedures to close defects, dilate narrowed vessels, or implant devices.
• Post-operative care and long-term follow-up are essential.
• Some patients may require lifelong monitoring and management to prevent complications and ensure optimal quality of life.