Basic Principle of Magnetic Resonance Imaging (MRI) | Radiological Physics

Radiographic Anatomy for Radiographers

Radiographic Anatomy

The bones of the upper limb, or extremities are grouped into hand, forearm, arm and shoulder girdle.

Hand:

The hand consists of 27 bones, which are subdivided into the following groups:

a.     Phalanges: bones of the digits (fingers and thumb)

b.     Metacarpals: bones of the palm

c.      Carpals: bones of the wrist

Digits:

The five digits are described by numbers and names. Beginning at the lateral, or thumb, side of the hand, the numbers and names are as follows:

First digit (thumb)

Second digit (index finger)

Third digit (middle finger)

Fourth digit (ring finger)

Fifth digit (small finger)

The digits contain a total of 14 phalanges (phalanx, singular), which are long bones that consist of a cylindric body and articular ends. Nine phalanges have two articular ends. The first digit has two phalanges- the proximal and distal. The other digits have three phalanges- the proximal, middle and distal. The proximal phalanges are the closest to the palm, and the distal phalanges are the farthest from the palm. The distal phalanges are small and flattened, with a roughened rim around their distal anterior end; this gives them a spatula-like appearance. Each phalanx has a head, body and base.

Metacarpals:

Five metacarpals, which are cylindric in shape and slightly concave anteriorly, form the palm of the hand. They are long bones consisting of a body and two articular ends, the head distally and the base proximally. The area below the head is the head is the neck where fractures often occur. The first metacarpal contains two small sesamoid bones on its palmar aspect below the neck. A single sesamoid is often seen at this same level on the second metacarpal. The metacarpal heads, commonly known as the knuckles, are visible on the dorsal hand in flexion. The metacarpals are also numbered 1 to 5, beginning from the lateral side of the hand.

Wrist:

The wrist has eight carpal bones, which are fitted closely together and arranged in two horizontal rows. The carpals are classified as short bones and are composed largely of cancellous tissue with an outer layer of compact bony tissue. These bones, with one exception, have two or three names. The proximal row of carpals, which is nearest the forearm, contains the scaphoid, lunate, triquetrum and pisiform. The distal row includes the trapezium, trapezoid, capitate and hamate.

Each carpal contains identifying characteristics. Beginning the proximal row of carpals on the lateral side, the scaphoid, the largest bone in the proximal carpal row, has a tubercle on the anterior and lateral aspect for muscle attachment and is palpable near the base of the thumb. The lunate articulates with the radius proximally and is easy to recognize because of its crescent shape. The triquetrum is roughly pyramidal and articulates anteriorly with the hamate. The pisiform is a pea-shaped bone situated anterior to the triquetrum and is easily palpated.

Beginning the distal row of carpals on the lateral side, the trapezium has a tubercle and groove on the anterior surface. The tubercles of the trapezium and scaphoid comprise the lateral margin of the carpal groove. The trapezoid has a smaller surface anteriorly than posteriorly. The capitate articulates with the base of the third metacarpal and is the largest and most centrally located carpal. The wedge-shaped hamate exhibits the prominent hook of hamate, which is located on the anterior surface. The hamate and the pisiform form the medial margin of the carpal groove.

A triangular depression is located on the posterior surface of the wrist and is visible when the thumb is abducted and extended. This depression, known as the anatomic snuffbox, is formed by the tendons of the two major muscles of the thumb. The anatomic snuffbox overlies the scaphoid bone and the radial artery, which carries blood to the dorsum of the hand. Tenderness in the snuffbox area is a clinical sign suggesting fracture of the scaphoid- the most commonly fractured carpal bone.

Carpal sulcus: the anterior or palmar surface of the wrist is concave from side to side and forms the carpal sulcus. The flexor retinaculum, a strong fibrous band attaches medially to the pisiform, and hook of hamate and laterally to the tubercles of the scaphoid and trapezium. The carpal tunnel is the passageway created between the carpal sulcus and flexor retinaculum. The median nerve and the flexor tendons pass through the carpal canal. Carpal tunnel syndrome results from compression of the median nerve inside the carpal tunnel.

Forearm:

The forearm contains two bones that lie parallel to each other- the radius and ulna. Like other long bones, they have a body and two articular extremities. The radius is located on the lateral side of the forearm, and the ulna is on the medial side.

Ulna:

The body of the ulna is long and slender and tapers inferiorly. The upper portion of the ulna is large and presents two beak-like processes and concave depressions. The proximal process, or olecranon process, concaves anteriorly and slightly inferiorly and forms the proximal portion of the trochlear notch. The more distal coronoid process projects anteriorly from the anterior surface of the body and curves slightly superiorly. The process is triangular and forms the lower portion of the trochlear notch. A depression called the radial notch is located on the lateral aspect of the coronoid process.

The distal end of the ulna includes a rounded process on its lateral side called the head and a narrower conic projection on the posteromedial side called the ulnar styloid process. An articular disk separates the head of the ulna from the wrist joint.

Radius:

The proximal end of the radius is small and presents a flat disk like head above a constricted area called the neck. Just inferior to the neck on the medial side of the body of the radius is a roughened process called radial tuberosity. The distal end of the radius is broad and flattened and has a conic projection on its lateral surface called the radial styloid process.

Arm:

The arm has one bone called humerus, which consists of a body and two articular ends. The proximal part of the humerus articulates with the shoulder girdle. The distal humerus is broad and flattened and presents numerous processes and depressions.

The entire distal end of the humerus is called the humeral condyle and includes two smooth elevations for articulation with the bones of the forearm- the trochlea on the medial side and the capitulum on the lateral side. The medial and lateral epicondyles are superior to the condyle and easily palpated. On the anterior surface superior to the trochlea, a shallow depression called the coronoid fossa receives the coronoid process when the elbow is flexed. The relatively small radial fossa, which receives the radial head when the elbow is flexed, is located lateral to the coronoid fossa and proximal to the capitulum. The olecranon fossa is a deep depression found immediately behind the coronoid fossa on the posterior surface and accommodates the olecranon process when the elbow is extended.

The proximal end of the humerus contains the head, which is large, smooth and rounded and lies in an oblique plane on the superomedial side. Just below the head, lying in the same oblique plane, is the narrow, constricted anatomic neck. The constriction of the body just below the tubercles is called the surgical neck, which is the site of many fractures.

The lesser tubercle is situated on the anterior surface of the bone immediately below the anatomic neck. The tendon of the subscapularis muscle inserts at the lesser tubercle. The greater tubercle is located on the lateral surface of the bone just below the anatomic neck and is separated from the lesser tubercle by a deep depression called the intertubercular groove.

Upper limb articulations:

The interphalangeal articulations between the phalanges are synovial hinge type and allow only flexion and extension. The interphalangeal joints are named by location and are differentiated as either proximal interphalangeal joint (PIP) or distal interphalangeal joint (DIP), by the digit number, and by right or left hand (e.g., the PIP articulation of the fourth digit of the left hand). Because the first digit has only two phalanges, the joint between the two phalanges is simply called the interphalangeal joint (IP).

The metacarpals articulate with the phalanges at their distal ends and the carpals at their proximal ends. The metacarpal phalangeal (MCP) articulations are synovial ellipsoidal joints and have the movements of flexion, extension, abduction, and circumduction. Because of the less convex and wider surface of the MCP joint of the thumb, only limited abduction and adduction are possible.

The carpals articulate with each other, the metacarpals, and the radius of the forearm. In the carpometacarpal (CMC) articulations, the first metacarpal and trapezium form a synovial saddle joint, which permits the thumb to oppose the fingers (touch the fingertips). The articulation between the second, third, fourth and fifth metacarpals and the trapezoid, capitate, and hamate, form synovial gliding joints. The intercarpal articulations are also synovial gliding joints. The articulations between lunate and scaphoid form a gliding joint. The radiocarpal articulation is a synovial ellipsoidal type. This type is formed by the articulation of the scaphoid, lunate and triquetrum, with the radius and the articular disk just distal to the ulna.

The distal and proximal radioulnar articulations are synovial pivot joints. The distal ulna articulates with the ulnar notch of the distal radius. The proximal head of the radius articulates with the radial notch of the ulna at the medial side. The movements of supination and pronation of the forearm and hand largely result from the combined rotary action of these two joints. In pronation the radius turn medially and crosses over the ulna at its upper third and the ulna makes a slight counter-rotation that rotates the humerus medially.

The elbow joint proper includes the proximal radioulnar articulation and the articulations between the humerus and the radius and ulna. The three joints are enclosed in a common capsule. The trochlea of the humerus articulates with the ulna at the trochlear notch. The capitulum of the humerus articulates with the flattened head of the radius. The humeroulnar and humeroradial articulations form a synovial hinge joint and allow only flexion and extension movement.

Fat pads:

The three areas of fat associated with the elbow joint can be visualized only in the lateral projection. The posterior fat pad covers the largest area and lies within the olecranon fossa of the posterior humerus. The superimposed coronoid and radial fat pads, which lie in the coronoid and radial fossae of the anterior humerus, form the anterior fat pad. The supinator fat pad is positioned anterior to and parallel with the anterior aspect of the proximal radius.

When the elbow is flexed 90⁰ for the lateral projection, only the anterior and the supinator fat pads are visible and the posterior fat pad is depressed within the olecranon fossa. The anterior fat pad somewhat resembles a teardrop. The fat pads become significant radiographically when an elbow injury causes effusion and displaces the fat pads or alters their shape. Visualization of the posterior fat pad is a reliable indicator of elbow pathology. Exposure factors designed to demonstrate soft tissues are extremely important on lateral elbow radiographs because visualization of the fat pads may be the only evidence of injury.

Pathology:

1.     Bone cyst: fluid-filled cyst with a wall of fibrous tissue

2.     Bursitis: inflammation of the bursa

3.     Dislocation: displacement of a bone from the joint space

4.     Fracture: disruption in the continuity of bone

5.     Bennett’s: fracture at the base of the first metacarpal

6.     Boxer’s: fracture of the metacarpal neck

7.     Colle’s: fracture of the distal radius with posterior (dorsal) displacement

8.     Smith’s: fracture of the distal radius with anterior (palmar)) displacement

9.     Torus or Buckle: impacted fracture with bulging of the periosteum

10.                        Gout: hereditary form of arthritis in which uric acid is deposited in joints

11.                        Joint effusion: accumulation of fluid in the joint associated with an underlying condition

12.                        Metastases: transfer of a cancerous lesion from one area to another

13.                        Osteoarthritis or Degenerative Joint Disease: form of arthritis marked by progressive cartilage deterioration in synovial joints and vertebrae

14.                        Osteomyelitis: inflammation of bone due to a pyogenic infection

15.                        Osteopetrosis: increased density of atypically soft bone

16.                        Osteoporosis: loss of bone density

17.                        Rheumatoid Arthritis: chronic, systemic, inflammatory collagen disease

18.                        Tumor: new tissue growth where cell proliferation is uncontrolled

19.                        Chondrosarcoma: malignant tumor arising from cartilage cells

20.                        Enchondroma: benign tumor arising from cartilage cells

21.                        Ewing’s sarcoma: malignant tumor of bone arising in medullary tissue

22.                        Osteosarcoma: malignant, primary tumor of bone with bone or cartilage formation

Shoulder Girdle:

The shoulder girdle is formed by two bones, the calvicle and scapula. Their function is to connect the upper limb to the trunk. Although the alignment of these two bones is considered a girdle, these two bones is considered a girdle, it is incomplete both in front and in back. The girdle is completed in front by the sternum, which articulates with the medial end of the clavicle. The scapulae are widely separated in the back.

Clavicle:

The clavicle, classified as a long bone, has a body and two articular extremities. The clavicle lies in a horizontal oblique plane just above the first rib and forms the anterior part of the shoulder girdle. The lateral aspect is termed the acromial extremity, and it articulates with the acromion process of the scapula. The medial aspect, termed the sternal extremity, articulated with the manubrium of the sternum and the first costal cartilage. The clavicle, which serves as a fulcrum for the movements of the arm, is doubly curved for strength. The curvature is more acute in males than in females.

Scapula:

The scapula, classified as a flat bone, forms the posterior part of the shoulder girdle. Triangular in shape, the scapula has two surfaces, three shape, three angles. Lying on the superoposterior thorax between the second and seventh ribs, the scapula’s medial border runs parallel with the vertebral column. The body of the bone is arched from top to buttom for greater strength, and its surface serve as the attachment sites of numerous muscles.

The costal (anterior) surface of the scapula is slightly concave and contains the subscapular fossa. It is filled almost entirely by the attachment of the subcapularis muscle. The anterior serratus muscle attaches to the medial border of the costal surface from the superior angle to the inferior angle.

The dorsal (posterior) surface is divided into two portions by a prominent spinous process. The crest of spine arises at the superior third of the medial border from a smooth, triangular area and runs obliquely superior to end in a flattened, ovoid projection called the acromion. The area above the spine is called the supraspinatous fossa and gies origin to the supraspinatus muscle. The infraspinatus muscle arises from the portion below the spine, which is called the infraspinatus fossa. The teres minor muscle arises from the superior two thirds of the lateral border of the dorsal surface and the teres major from the distal third and the inferior angle. The dorsal surface of the medial border affords attachment of the levator muscles of the scapulae, greater rhomboid muscle, and lesser rhomboid muscle.

The superior border extends from the superior angle to the coracoid process and at its lateral end has a deep depression, the scapular notch. The medial border extends from the superior to the inferior angles. The lateral border extends from the glenoid cavity to the inferior angle.

The superior angle is formed by the junction of the superior and medial borders. The inferior angle is formed by the junction of the medial (vertebral) and lateral borders and lies over the seventh rib. The lateral angle, the thickest part of the body of the scapula, ends in a shallow, oval depression called the glenoid cavity. The constricted region around the glenoid cavity is called the neck of the scapula. The coracoid process arises from a thick base that extends from the scapular notch to the superior portion of the neck of the scapula. This process projects first anteriorly and medially and then curves on itself to project laterally. The coracoid process can be palpated just distal and slightly medial to the acromioclavicular articulation.

Humerus:

The proximal end of the humerus consists of a head, an anatomic neck, two prominent processes called the greater and lesser tubercles, and the surgical neck. The head is large, smooth, and rounded and it lies in an oblique plane on the superomedial side of the humerus. Just below the head, lying in the same oblique plane, is the narrow, constricted anatomic neck. The constriction of the body just below the tubercles is called the surgical neck, which is the site of many fractures.

The lesser tubercle is situated on the anterior surface of the bone, immediately below the anatomic neck. The tendon of the subscapular muscle inserts at the lesser tubercle. The greater tubercle is located on the lateral surface of the bone, just below the anatomic neck, and is separated from the lesser tubercle by a deep depression called the intertubercular (bicipital groove). The superior surface of the greater tubercle slopes posteriorly at an angle of approximately 25⁰ and has three flattened impressions for muscle insertions. The anterior impression is the highest of the three and affords attachment to the tendon of the supraspinatus muscle. The middle impression is the point of insertion of the infraspinatus muscle. The tendon of the upper fibers of the teres minor muscle inserts at the posterior impression (the lower fibers insert into the body of the body immediately below this point).

Bursae are small, synovial fluid-filled sacs that relieve pressure and reduce friction in tissue. They are often found between the bones and the skin, and they allow the skin to move easily when the joint is moved. Bursae are found also between bones and ligaments, muscles, or tendons. One of the largest bursae of the shoulder is the subacromial bursae. It is located under the acromion process and lies between the deltoid muscle and the shoulder joint capsule. The subacromial bursa does not normally communicate with the joint. Other bursae of the shoulder are found superior to the acromion, between the coracoid process and the joint capsule, and between the capsule and the tendon of the subscapular muscle. Bursae become important radiographically when injury or age causes the deposition of calcium.

Shoulder Girdle Articulations:

Scapulohumeral articulation:

The scapulohumeral articulation between the glenoid cavity and the head of the humerus forms a synovial ball-and –socket joint, allowing movement in all directions. This joint is often referred to as the glenohumeral joint. Although many muscles connect with, support and enter into the function of the shoulder joint, radiographers are chiefly concerned with the insertion points of the short rotator cuff muscles.

Structural classification of joints of the shoulder girdle:

Joint	Tissue	Type	Movement
Scapulohumeral	Synovial	Ball and socket	Freely movable
Acromioclavicular	Synovial	Gliding	Freely movable
Sternoclavicular	Synovial	Double gliding	Freely movable

An articular capsule completely encloses the shoulder joint. The tendon of the long head of the biceps brachii muscle, which arises from the superior margin of the glenoid cavity, passes through the capsule of the shoulder joint, goes between its fibrous and synovial layers, arches over the head of the humerus, and descends through the intertubercular (bicipital) groove. The short head of the biceps arises from the coracoid process and, with the long head of the muscle, inserts in the radial tuberosity. Because it crosses with both the shoulder and elbow joint, the biceps help synchronize their action.

The interaction of movement among the wrist, elbow, and shoulder joints makes the position of the hand important in radiography of the upper limb. Any rotation of the hand also rotates the joints. The best approach to the study of the mechanics of joint and muscle action is to perform all movements ascribed to each joint and carefully note the reaction in remote parts.

Acromioclavicular articulation:

The acromioclavicular (AC) articulation between the acromion process of the scapula and the acromial extremity of the clavicle forms a synovial gliding joint. It permits both gliding and rotary (elevation, depression, protraction, and retraction) movement. Because the end of the clavicle rides higher than the adjacent surface of the acromion, the slope of the surfaces tends to favor displacement of the acromion downward and under the clavicle.

Sternoclavicular articulation:

The sternoclavicular (SC) articulation is formed by the sternal extremity of the clavicle with two bones: the manubrium and the first rib cartilage.

The union of the clavicle with the manubrium of the sternum is the only bony union between the upper limb and trunk. This articulation is a synovial double-gliding joint. However, the joint is adapted by a fibrocartilaginous disk to provide movements similar to a ball-and-socket joint: circumduction, elevation, depression and forward and backward movements. The clavicle carries the scapula with it through any movement.

Pathology:

1.     Bursitis: inflammation of the bursa

2.     Dislocation: displacement of a bone from the joint space

3.     Fracture: disruption in the continuity of bone

4.     Hills-Sachs Defect: impacted fracture of the posterolateral aspect of the humeral head with dislocation

5.     Metastases: transfer of a cancerous lesion from one area to another

6.     Osteoarthritis or Degenerative Joint Disease: form of arthritis marked by progressive cartilage deterioration in synovial joints and vertebrae

7.     Osteopetrosis: increased density of atypically soft bone

8.     Osteoporosis: loss of bone density

9.     Rheumatoid Arthritis: chronic, systemic, inflammatory collagen disease

10.                        Tendonitis: inflammation of the tendon and tendon-muscle attachment

11.                        Tumor: new tissue growth where cell proliferation is uncontrolled

12.                        Chondrosarcoma: malignant tumor arising from cartilage cells

Lower limb:

The lower limb, or extremity and its girdle are studied in four parts:

a.     Foot

b.     Leg

c.      Thigh

d.     Hip

Foot:

The foot consists of 26 bones.

14 phalanges (bones of the toes)

5 metatarsals (bones of the instep)

7 tarsals (bones of the ankle)

The bones of the foot are similar to those of the hand. The structural differences, however, permit walking and support of the body’s weight. The foot is divided into forefoot, midfoot and hindfoot. The forefoot includes the metatarsals and toes. The midfoot includes 5 tarsals- the cuneiform, navicular and cuboid bones. The hindfoot includes the talus and calcaneus. The bones of the foot are shaped and joined together to form a series of longitudinal and transverse arches. The longitudinal arch functions as a shock absorber to distribute the weight of the body in all directions, which permits smooth walking. The transverse arch runs from side to side and assists in supporting the longitudinal arch. The superior surface of the foot is termed the dorsum or dorsal surface, and the inferior, or posterior aspect of the foot is termed the plantar surface.

Phalanges:

Each foot has 14 phalanges- two in the great toe and three in each of the other toes. The phalanges of the great tow are termed the distal and proximal phalanges. Those of the other toes are termed the proximal, middle and distal phalanges. Each phalanx is composed of a body and two expanded articular ends- the proximal base and the distal head.

Metatarsals:

The five metatarsals are numbered one to five beginning at the medial or great toe side of the foot. The metatarsals consist of a body and two articular ends. The expanded proximal end is called the base, and the small, rounded distal end is termed the head. The five heads form the “ball” of the foot. The first metatarsal is the shortest and thickest. The second metatarsal is the longest. The base of the fifth metatarsal contains a prominent tuberosity which is a common site of fractures.

Tarsals:

The proximal foot contains seven tarsals.

Calcaneus

Talus

Navicular bone

Cuboid

Medial cuneiform

Intermediate cuneiform

Lateral cuneiform

Beginning at the medial side of the foot, the cuneiforms are described as medial, intermediate and lateral.

The calcaneus is the largest and strongest tarsal bone and is also termed as “os calcis”. It projects posteriorly and medially at the distal part of the foot. It projects posteriorly and medially at the distal part of the foot. The long axis of the calcaneus is directed inferiorly and forms an angle of approximately 30⁰. The posterior and inferior portions of the calcaneus contain the posterior tuberosity for attachment of the Achilles tendon. Superiorly, three articular facets join with the talus. They are called the anterior, middle and posterior facets. Between the middle and posterior talar articular facets is a groove, the calcaneal sulcus, which corresponds to a similar groove on the inferior surface of the talus. Collectively these sulci comprise the sinus tarsi. The medial aspect of the calcaneus extends outward as a shelflike overhang and is termed the sustentaculum tali. The lateral surface of the calcaneus contains the trochlea.

The talus, irregular in form and occupying the most superior portion of the foot, is the second largest of the tarsal bones. The talus articulates with four bones- the tibial, fibula, calcaneus and navicular bone. The superior surface, the trochlear surface, articulates with the tibia and connects the foot to the leg. The head of the talus is directed anteriorly and has articular surfaces that joint the navicular bone and calcaneus. On the inferior surface is a groove, the sulcus tali, that forms the roof of the sinus tarsi. The inferior surface also contains three facets that align with the facets on the superior surface of the calcaneus.

The cuboid bone lies on the lateral side of the foot between the calcaneus and the fourth and fifth metatarsals. The navicular bone lies on the medial side of the foot between the talus and the three cuneiforms. The cuneiforms lie at the central and medial aspect of the foot between the navicular bone and the first, second, and third metatarsals. The medial cuneiform is the largest of the three cuneiform bones, and the intermediate is the smallest.

The seven tarsals can be remembered using the following mnemonic:

Chubby Calcaneus

Twisted Talus

Never Navicular

Could Cuboid

Cha Cuneiform- medial

Cha Cuneiform- intermediate

Cha Cuneiform- lateral

Sesamiod bones:

Beneath the head of the first metatarsal are two small bones called sesamoid bones. They are detached from the foot and embedded within two tendons. These bones are seen on most adult foot radiographs. They are a common site of fractures and must be demonstrated radiographically.

Leg:

The leg has two bones: the tibia and fibula. The tibia, second largest bone in the body, is situated on the medial side of the leg and is a weight-bearing bone. Slightly posterior to the tibia on the lateral side of the leg is the fibula. The fibula does not bear any body weight.

Tibia:

The tibia is the larger of the two bones of the leg and consists of one body and two expanded extremities. The proximal end of the tibia has two prominent processes- the medial and lateral condyles. The superior surfaces of the condyles form smooth facets for articulation with the condyles of the femur. These two flatlike superior surfaces are called the tibial plateaus, and they slope posteriorly about 10⁰ to 20⁰. Between the two articular surfaces is sharp projection, the intercondylar eminence, which terminates in two peaklike processes called the medial and lateral intercondylar tubercles. The lateral condyle has a facet at its distal posterior surface for articulation with the head of the fibula. On the anterior surface of the tibia, just below the condyles, is a prominent process called the tibial tuberosity, to which the ligamentum patellae attaches. Extending along the anterior surface of the tibial body, beginning at the tuberosity, is a sharp ridge called the anterior crest.

The distal end of the tibia is broad, and its medial surface is prolonged into a large process called the medial malleolus. Its anterolateral surface contains the anterior tubercle, which overlays the fibula. The lateral surface is flattened and contains the triangular fibular notch for articulation with the fibula. The surface under the distal tibia is smooth an shaped for articulation with the talus.

Fibula:

The fibula is slender in comparison to its length and consists of one body and two articular extremities. The proximal end of the fibula is expanded into a head, which articulates with the lateral condyle of the tibia. As the lateroposterior aspect of the head is a conic projection called the apex. The enlarged distal end of the fibula is the lateral malleolus. The lateral malleolus is pyramidal and marked by several depressions at its inferior and posterior surfaces. Viewed axially, the lateral malleolus lies approximately 15⁰ to 20⁰ more posterior than the medial malleolus.

Femur:

The femur is the longest, strongest, and heaviest bone in the body. This bone consists of one body and two articular extremities. The body is cylindrical, slightly convex anteriorly and slants medially from 5⁰ to 15⁰. The extent of medial inclination depends on the breath of the pelvic girdle. When the femur is vertical, the medial condyle is lower than the lateral condyle. About a 5⁰ to 7⁰ difference exists between the two condyles. Because of this difference, on lateral radiographs of the knee the central ray is angled 5⁰ to 7⁰ cephalad to “open” the joint space of the knee. The superior portion of the femur articulates with the acetabulum of the hip joint.

The distal end of the femur is broadened and has two large eminence; the larger medial condyle and the smaller lateral condyle. Anteriorly the condyles are separated by the patellar surface, a shallow, triangular area superior to the intercondylar fossa on the posterior femur is the popliteal surface, over which the popliteal blood vessels and nerves pass.

The posterior area of the knee, between the condyles, contains a sesamoid bone in 3 to 5% of people. This sesamoid bone is called the fabella and is only seen on the lateral projection of the knee.

Patella:

The patella, or knee cap is the largest and most constant sesamoid bone in the body. The patella is a flat, triangular bone situated at the distal anterior surface of the femur. The patella develops in the tendon of the quadriceps femoris muscle between the ages of 3 and 5 years. The apex, or tip is directed inferiorly, lies half inch above the joint space of the knee, and is attached to the tuberosity of the tibia by the patellar ligament. Interestingly, the superior border of the patella is called the base.

Knee Joint:

The knee joint is one of the most complex joints in the human body. The femur, tibia, fibula, and patella are held together by a complex group of ligaments. These ligaments work together to provide stability for the knee joint. Although radiographers do not produce images of these ligaments, they need to have a basic understanding of their positions and interrelationship. Many patients with knee injuries do not have fractures, but they have torn one or more of these ligaments, which can cause great pain and may alter the position of the bones. The important ligaments of the knee are:

a.     Posterior cruciate ligament

b.     Anterior cruciate ligament

c.      Tibial collateral ligament

d.     Fibular collateral ligament

The knee joint contains two fibrocartilage disks called the lateral and medial meniscus. The circular menisci lie on the tibial plateau. They are thick at the outer margin of the joint and taper off toward the center of the tibial plateau. The center of the tibial plateau contains cartilage that articulates directly with the condyles of the knee. The menisci provide stability for the knee and also act as a shock absorber. The menisci are commonly torn during injury. either a knee arthrogram or a magnetic resonance imaging (MRI) can must be performed to visualize a meniscus tear

Lower limb articulations:

The joints of the lower limb are summarized in table below. Beginning with the most distal portion of the lower limb, the articulations are as follows:

Joint Classification of the lower limb:

Joint	Tissue	Type	Movement
Interphalangeal	Synovial	Hinge	Freely movable
Metatarsophalangeal	Synovial	Ellipsoidal	Freely movable
Intermetatarsal	Synovial	Gliding	Freely movable
Tarsometatarsal	Synovial	Gliding	Freely movable
Calcaneocuboid	Synovial	Gliding	Freely movable
Cuneocuboid	Synovial	Gliding	Freely movable
Intercuneiform	Synovial	Gliding	Freely movable
Cuboidonavicular	Fibrous	Syndesmosis	Slightly movable
Naviculocuneiform	Synovial	Gliding	Freely movable
Subtalar:
Talocalcaneal	Synovial	Gliding	Freely movable
Talocalcaneonavicular	Synovial	Ball and socket	Freely movable
Ankle mortise:
Talofibular	Synovial	Hinge	Freely movable
Tibiotalar	Synovial	Hinge	Freely movable
Tibiofibular
Proximal	Synovial	Gliding	Freely movable
Distal	Fibrous	Syndesmosis	Slightly movable
Knee:
Patellofemoral	Synovial	Gliding	Freely movable
Femorotibial	Synovial	Hinge modified	Freely movable

                  

The interphalangeal (IP) articulations, between the phalanges, are synovial hinges that allow only flexion and extension. The joints between the distal and middle phalanges are the distal interphalangeal (DIP) joints. Articulations between the middle and proximal phalanges are the proximal interphalangeal (PIP) joints. With only two phalanges in the great toe, the joint is known simply as the interphalangeal joint.

The distal heads of the metatarsals articulate with the proximal ends of the phalanges at the metatarsophalangeal (MTP) articulations to form synovial ellipsoidal joints, which have movements of flexion, extension, and slight adduction and abduction. The proximal bases of the metatarsals articulate with one another (intermetatarsal articulations) and with the tarsals (intermetatarsal articulations) and with the tarsals (tarsometatarsal TMT) articulations to form synovial gliding joints, which permit flexion, extension, adduction and abduction movements.

The intertarsal articulations allow only slight gliding movements between the bones and are classified as synovial gliding or synovial ball and socket joints. The joint spaces are narrow and obliquely situated. When the joint surfaces of these bones are in question, adjust the foot to place the joint spaces parallel with the central ray.

The calcaneus supports the talus and articulates with it by an irregualarly shaped, three faceted joint surface, forming the subtalar joint. This joint is classified as synovial gliding. Anteriorly the calcaneus articulates with the cuboid at the calcaneocuboid joint. This joint is a synovial gliding joint. The talus rests on the top of the calcaneus. It articulates with the navicular bone anteriorly, supports the tibia above, and articulates with the malleoli of the tibia and fibula at its sides.

Each of the three parts of the subtalar joint is formed by reciprocally shaped facets on the inferior surface of the talus and the superior surface of the calcaneus. Study of the superior and medial aspects of the calcaneus will help the radiographer to better understand the problems involved in radiography of this joint.

The intertarsal articulations are as follows.

a.     Calcaneocuboid

b.     Cuneocuboid

c.      Intercuneiform (2)

d.     Cuboidonaviular

e.      Naviculocuneiform

f.       Talocalcaneal

g.     Talocalcaneonavicular

The ankle joint is commonly called the ankle mortise, or mortise joint. It is formed by the articulations between the lateral malleolus of the fibula and the inferior surface and medial malleolus of the tibia. The mortise joint is often divided specifically into the talofibular and tibiofibular joints. These form a socket type of structure that articulates with the superior portion of the talus. The talus fits inside the mortise. The articulation is a synovial hinge type of joint. The primary action of the ankle joint is dorsiflexion (flexion) and plantar flexion (extension); however, in full plantar flexion, a small amount of rotation and abduction adduction is permitted. The mortise joint allows inversion and eversion of the foot. Other movements at the ankle largely depend on the gliding movements of the intertarsal joints, particularly the one between the talus and calcaneus.

The fibula articulates with the tibia at both its distal and proximal ends. The distal tibiofibular joint is a fibrous syndesmosis joint allowing a slight movement. The head of the fibula articulates with the posteroinferior surface of the lateral condyle of the tibia, which forms the proximal tibiofibular joint, which is a synovial gliding joint.

The patella articulates with the patellar surface of the femur and protects the front of the knee joint. This articulation is called the patellofemoral joint; when the knee is extended and relaxed, the patella is freely movable over the patellar surface of the femur. When the knee is flexed, which is also a synovial gliding joint, the patella is locked in position in front of the patellar surface. The knee joint, or femorotibial joint, is the largest joint in the body. It is called a synovial modified hinge joint. In addition to flexion and extension, the knee joint allows slight medial and lateral rotation in flexed position. The joint is enclosed in an articular capsule and held together by numerous ligaments.

Pathology:

1.     Bone cyst: fluid filled cyst with a wall of fibrous tissue

2.     Congenital clubfoot: abnormal twisting of the foot, usually inward and downward

3.     Dislocation: displacement of a bone from the joint space

4.     Fracture: disruption in the continuity of bone

5.     Pott’s: avulsion fracture of the medial malleolus with loss of the ankle mortise

6.     Jones: avulsion fracture of the base of the fifth metatarsal

7.     Gout: hereditary form of arthritis in which uric acid is deposited in joints

8.     Metastases: transfer of a cancerous lesion from one area to another

9.     Osgood-schlatter disease: incomplete separation or avulsion of the tibial tuberosity

10.                        Osteoarthritis or Degenerative Joint Disease: form of arthritis marked by progressive cartilage deterioration in synovial joints and vertebrae

11.                        Osteomalacia or Rickets: softening of the bones due to a vitamin D deficiency

12.                        Osteomyelitis: inflammation of bone due to a pyogenic infection

13.                        Osteopetrosis: increased density of atypically soft bone

14.                        Osteoporosis: loss of bone density

15.                        Paget’s disease: chronic metabolic disease of bone marked by weakened, deformed and thickened bone that fractures easily

16.                        Tumor: new tissue growth when cell proliferation is uncontrolled

17.                        Chondrosarcoma: malignant tumor arising from cartilage cells

18.                        Enchondroma: benign tumor consisting of cartilage

19.                        Ewing’s sarcoma: malignant tumor of bone arising in medullary tissue

20.                        Osteochondroma or exostosis: benign bone tumor projection with a cartilaginous cap

21.                        Osteoclastoma or Giant Cell Tumor: lucent lesion in the metaphysis, usually at the distal femur

22.                        Osteoid osteoma: a benign lesion of cortical bone

23.                        Osteosarcoma: malignant, primary tumor of bone with bone or cartilage formation

Pelvis and upper femora:

The pelvis serves as a base for the trunk and a girdle for the attachment of the lower limbs. The pelvis consists of four bones: two hip bones, the sacrum, and the coccyx. The pelvic girdle is composed of only the two hip bones, however.

Hip bone:

The hip bone is often referred to as the os coxae, also the innominate bone.

The hip bone consists of the ilium, pubis and ischium. These three bones join together to form the acetabulum, the cup-shaped socket that receives the head of the femur. The ilium, pubis and ischium are separated by cartilage in youth but become fused into one bone in adulthood.

Ilium:

The ilium consists of a body, and a broad curved portion called the ala. The body of the ilium forms approximately two fifths of the acetabulum superiorly. The ala projects superiorly from the body to form the prominence of the hip. The ala has three borders: anterior, posterior and superior. The anterior and posterior borders present four prominent projections:

a.     Anterior superior iliac spine

b.     Anterior inferior iliac spine

c.      Posterior superior iliac spine

d.     Posterior inferior iliac spine

The anterior superior iliac spine (ASIS) is an important and frequently used radiographic positioning reference point. The superior margin extending from the ASIS to the posterior superior iliac spine is called the iliac crest. The medial surface of the wing contains the iliac fossa and is separated from the body of the bone by a smooth, arc-shaped ridge, the arcuate line, which forms a part of the circumference of the pelvic brim. The arcuate line passes obliquely, inferiorly and medially to its junction with the pubis. The inferior and posterior portions of the wing present a large, rough surface- the auricular surface- for articulation with the sacrum. This articular surface and the articular surface of the adjacent sacrum have irregular elevations and depressions that cause a partial interlock of the two bones. Below this surface the ilium curves inward, forming the greater sciatic notch.

Pubis:

The pubis consists of a body, the superior ramus and the inferior ramus. The body of the pubis forms approximately one fifth of the acetabulum anteriorly. The superior ramus projects inferiorly and medially from the acetabulum to the midline of the body. There the bone curves inferiorly and then posteriorly and laterally to join the ischium. The lower prong is termed the inferior ramus.

Ischium:

The ischium consists of a body and the ischial ramus. The body of the ischium forms approximately two fifths of the acetabulum posteriorly. It projects posteriorly and inferiorly from the acetabulum to form an expanded portion called the ischial tuberosity. When the body is in a seated-upright position, its weight rests on the two ischial tuberosities. The ischial ramus projects anteriorly and medially from the tuberosity to its junction with the inferior ramus of the pubis. By this posterior union the rami of the pubis and ischium enclose the obturator foramen. At the superoposterior border of the body is a prominent projection called the ischial spine. Just below the ischial spine is an indentation, the lesser sciatic notch.

Proximal femur:

The femur is the longest, strongest and heaviest bone in the body. The proximal end of the femur consists of a head, a neck and two large processes: the greater and lesser trochanters. The smooth, rounded head is connected to the femoral body by a pyramid-shaped neck and is received into the acetabular cavity of the hip bone. A small depression at the center of the head, the fovea capitis attaches to the ligamentum capitis femoris. The neck is constricted near the head but expands to a broad base at the body of the bone. The neck projects medially, superiorly and anteriorly from the body. The trochanters are situated at the junction of the body and the base of the neck. The greater trochanter is at the superolateral part of the femoral body, and the lesser trochanter is at the posteromedial part. The prominent ridge extending between the trochanters at the base of the neck on the posterior surface of the body is called the intertrochanteric crest. The less prominent ridge connecting the trochanters anteriorly is called the intertrochanteric line. The femoral neck and the intertrochanteric crest are two common sites of fractures in the elderly. The superior portion of the greater trochanter projects above the neck and curves slightly posteriorly and medially.

The angulation of the neck of the femur varies considerably with age, sex and stature. In the average adult the neck projects anteriorly from the body at an angle of approximately 15 to 20⁰ and superiorly at an angle of approximately 120 to 130⁰ to the long axis of the femoral body. The longitudinal plane of the femur is angled about 10⁰ from vertical. In youth the latter angle is wider; that is, the neck is more vertical in position. In wide pelvises the angle is narrower, placing the neck in a more horizontal position.

Articulations of the Pelvis:

The articulation between the acetabulum and the head of the femur (the hip joint) is a synovial ball and socket joint that permits free movement in all directions. The knee and ankle joints are hinge joints; thus, the wide range of motion of the lower limb depends on the ball and socket joint of the hip. Because the knee and the ankle joints are hinge joints, medial and lateral rotations of the foot cause rotation of the entire limb, which is centered at the hip joint.

The pubis of the hip bones articulate with each other at the anterior midline of the body, forming a joint called the pubic symphysis. The pubic symphysis is a cartilaginous symphysis joint.

The right and left ilia articulate with the sacrum posteriorly at the sacroiliac (SI) joints. These two joints angle 25 to 30⁰ relative to the midsagittal plane. The SI articulations are synovial, irregular gliding joints. Because the bones of the SI joints interlock, movement is limited or nonexistent.

Classification of joints of pelvis and upper femora:

Joint	Tissue	Type	Movement
Hip joint	Synovial	Ball and socket	Freely movable
Pubic symphysis	Cartilaginous	Symphysis	Slightly movable
Sacroiliac	Synovial	Irregular gliding	Slightly movable

Female and male pelvis characteristics:

Feature	Female	Male
Shape	Wide, shallow	Narrow, deep
Bony structure	Light	Heavy
Superior aperture (inlet)	Oval	Round
Inferior aperture (outlet)	Wide	Narrow

Pelvis:

The female pelvis is lighter in structure than the male pelvis. It is wider and shallower, and the inlet is larger and more oval shaped. The sacrum is wider, it curves more sharply posteriorly, and the sacral promontory is flatter. The width and depth of the pelvis vary with stature and gender. The female pelvis is shaped for childbearing and delivery.

The pelvis is divided into two portions by an oblique plane that extends from the upper margin of the sacrum to the upper margin of the pubic symphysis. The boundary line of this plane is called the brim of the pelvis. The region above the brim is called the false or greater pelvis, and the region below the brim is called the true or lesser pelvis.

The brim forms the superior aperture, or inlet of the true pelvis. The inferior aperture, or outlet, of the true pelvis is measured from the tip of the coccyx to the inferior margin of the pubic symphysis in the anteroposterior direction and between the inlet and the outlet is called the pelvic cavity.

When the body is in the upright or seated position, the brim of the pelvis forms an angle of approximately 60⁰ to the horizontal plane. This angle varies with other body positions: the degree and direction of the variation depend on the lumbar and sacral curves.

Localizing anatomic structures:

The bony landmarks used in radiography of the pelvis and hips are as follows:

a.     Iliac crest

b.     ASIS

c.      Pubic symphysis

d.     Greater trochanter of the femur

e.      Ischial tuberosity

f.       Tip of the coccyx

Most of these points are easily palpable, even in hypersthenic patients. However, because of the heavy muscles immediately above the iliac crest, care must be exercised in locating this structure to avoid centering errors. Having the patient inhale deeply is advisable; while the muscles are relaxed during expiration, the radiographer should palapate for the highest point of the iliac crest.

The highest point of the greater trochanter, which can be palpated immediately below the depression in the soft tissues of the lateral surface of the hip, is in the same horizontal plane as the midpoint of the hip joint and the coccyx. The most prominent point of the greater trochanter is in the same horizontal plane as the pubic symphysis.

The greater trochanter is most prominent laterally and most easily palpated when the lower leg is medially rotated. When properly used, medial rotation assists in localization of hip and pelvis centering points and avoids distortion of the proximal end of the femur during radiography. Improper rotation of the lower leg can rotate the pelvis. Consequently, positioning of the lower leg is important in radiography of the hip and the pelvis; the feet must be immobilized in the correct position to avoid distortion of the image. Traumatic injuries or pathologic conditions of the pelvis or lower limb may rule out the possibility of medial rotation.

The pubic symphysis can be palpated on the midsagittal plane and on the same horizontal plane as the greater trochanters. By placing the fingertips at this location and performing a brief downward palpation with the hand flat, palm down and fingers together, the radiographer can locate the superior margin of the pubic symphysis. To avoid possible embarrassment or misunderstanding, the radiographer should advise the patient in advance that this and other palpations of pelvic landmarks are part of normal procedure and necessary for an accurate examination. When carried out in an efficient and professional manner with respect for the patient’s condition, such palpations are generally well tolerated.

The hip joint can be located by palpating the ASIS and the superior margin of the pubic symphysis. The midpoint of a line drawn between these two points is directly above the center of the dome of the acetabular cavity. A line drawn at right angles to the midpoint of the first line lies parallel to the long axis of the femoral neck of an average adult in the anatomic position. The femoral head lies one and half inches distal, and the femoral neck is two and half inches distal to this point.

For accurate localization of the femoral neck in atypical patients or in those in whom the limb is not in the anatomic position, a line is drawn between the ASIS and the superior margin of the pubic symphysis and a second line is drawn from a point one inch inferior to the greater trochanter to the midpoint of the previously marked line. The femoral head and neck lies along this line.

Pathology:

1.     Ankylosing spondylitis: rheumatoid arthritis variant involving the sacroiliac joints and spine

2.     Congenital Hip Dysplasia: malformation of the acetabulum causing displacement of the femoral head

3.     Dislocation: displacement of a bone from the joint space

4.     Fracture: disruption in the continuity of bone

5.     Legg-Calve-Perthes Disease: flattening of the femoral head due to vascular interruption

6.     Metastases: transfer of a cancerous lesion from one area to another

7.     Osteoarthritis or Degenerative Joint Disease: form of arthritis marked by progressive cartilage deterioration in synovial joints and vertebrae

8.     Osteopetrosis: increased density of atypically soft bone

9.     Osteoporosis: loss of bone density

10.                        Paget’s Disease: thick, soft bone marked by bowing and fractures

11.                        Slipped epiphyses: proximal portion of femur dislocated from distal portion at the proximal epiphyses

12.                        Tumor: new tissue growth where cell proliferation is uncontrolled

13.                        Chondrosarcoma: malignant tumor arising from cartilage cells

14.                        Multiple myeloma: malignant neoplasm of plasma cells involving the bone marrow and causing destruction of the bone

Vertebral column:

The vertebral column, or spine forms the central axis of the skeleton and is centered in the midsagittal plane of the posterior part of the trunk. The vertebral column has many functions: it encloses and protects the spinal cord; it acts as a support for the trunk; it supports the skeletal superiorly; and it provides for attachment for the deep muscles of the back and the rib laterally. The upper limbs are supported indirectly via the ribs, which articulate with the sternum. The sternum in turn articulates with the shoulder girdle. The vertebral column articulates with each hip bone at the sacroiliac joints. This articulation supports the vertebral column and transmits the weight of the trunk through the hip joints and the lower limbs.

The vertebral column is composed of small segments of bone called vertebrae. Disks of fibrocartilage are interposed between the vertebrae and acts as cushions. The vertebral column is held together by ligaments, and it is jointed and curved so that it has considerable flexibility and resilence.

In early life the vertebral column usually consists of 33 small, irregularly shaped bones. These bones are divided into five groups and named according to the region they occupy. The most superior seven vertebrae occupy the region of the neck and are termed cervical vertebrae. The succeeding 12 bones lie in the dorsal, or posterior portion of the thorax and are called the thoracic vertebrae. The five vertebrae occupying the region of the loin are termed lumbar vertebrae. The next five vertebrae, located in the pelvic region, are termed sacral vertebrae. The terminal vertebrae, also in the pelvic region, vary from three to five in number in the adult and are called the coccygeal vertebrae.

The 24 vertebral segments in the upper three regions remain distinct throughout life and are termed the true or movable vertebrae. The pelvic segments in the two lower regions are called false or fixed vertebrae because of the change they undergo in adults. The sacral segments usually fuse into one bone called the sacrum, and the coccygeal segments, referred to as the coccyx, also fuse into one bone.

Vertebral curvature:

Viewed from the side, the vertebral column has four curves that arch anteriorly and posteriorly from the midcoronal plane of the body. The cervical, thoracic, lumbar and pelvic curves are named for the regions they occupy. The normal lumbar curve can be referred as concave posteriorly. The cervical and lumbar curves which are convex anteriorly, are called lordotic curves. The thoracic and pelvic curves are concave anteriorly and are called kyphotic curves. The cervical and thoracic curves merge smoothly.

The lumbar and pelvic curves join at an obtuse angle termed the lumbosacral angle. The acuity of the angle in the junction of these curves varies in different patients. The thoracic and pelvic curves are called primary curves because they are present at birth. The cervical and lumbar curves are called secondary or compensatory curves because they develop after birth. The cervical curve, which is least pronounced of the curves, develops when the child begins to hold the head up at about 3 or 4 months of age and begins to sit alone at about 8 or 9 months of age. The lumbar curve develops when the child begins to walk at about 1 to 1.5 years of age. The lumbar and pelvic curves are more pronounced in females, who therefore have a more acute angle at the lumbosacral junction.

Any abnormal increase in the anterior concavity (or posterior convexity) of the thoracic curve is termed kyphosis. Any abnormal increase in the anterior convexity (or posterior concavity) of the lumbar or cervical curve is termed lordosis.

In frontal view, the vertebral column varies in width in several regions. Generally, the width of the spine gradually increases from the second cervical vertebra to the superior part of the sacrum and then decreases sharply. A slight lateral curvature is sometimes present in the upper thoracic region. The curve is to the right in right handed persons and to the left in left handed persons. For this region, lateral curvature of the vertebral column is believed to be the result of muscle action and to be influenced by occupation. An abnormal lateral curvature of the spine is called scoliosis. This condition also causes the vertebrae to rotate toward the concavity. The vertebral column then develops a second or compensatory curve in the opposite direction to keep the head centered over the feet.

Typical vertebra:

A typical vertebra is composed of two main parts- an anterior mass of bone called the body and a posterior ring like portion called the vertebral arch, and a space called the vertebral foramen. In the articulated column, the vertebral foramina form the vertebral canal.

The body of the vertebra is approximately cylindric in shape and is composed of largely cancellous bony tissue covered by a layer of compact tissue. From the superior aspect of the posterior surface is flattened, and from the lateral aspect the anterior and lateral surfaces are concave. The superior and inferior surfaces of the bodies are flattened and covered by a thin plate of articular cartilage.

In the articulated spine, the vertebral bodies are separated by intervertebral disks. These disks account for approximately one fourth of the length of the vertebral column. Each disk has a central mass of soft, pulpy, semigelatinous material called the nucleus pulposus, which is surrounded by an outer fibrocartilaginous disk called the annulus fibrosus. It is fairly common for the pulpy nucleus to rupture or protrude into the vertebral canal, thereby impinging on a spinal nerve. This condition is called herniated nucleus pulposus (HNP), or more commonly slipped disk. HNP most often occurs in the lumbar region as a result of improper body mechanics, and it can cause considerable discomfort and pain.

The vertebral arch is formed by two pedicles and two laminae that support four articular processes, two transverse processes and one spinous process. The pedicles are short, thick processes that project posteriorly, one from each side, from the superior and lateral parts of the posterior surface of the vertebral body. The superior and inferior surfaces of the pedicles or roots are concave. These concavities are called vertebral notches. By articulation with the vertebrae above and below, the notches form intervertebral foramina for the transmission of spinal nerves and blood vessels. The broad, flat laminae are directed posteriorly and medially from the pedicles.

The transverse processes project laterally and slightly posteriorly from the junction of the pedicles and laminae. The spinous process projects posteriorly and inferiorly from the junction of the laminae in the posterior midline. A congenital defect of the vertebral column in which the laminae fail to unite posteriorly at the midline is called spina bifida. In serious cases of spina bifida the spinal cord may protrude from the affected individual’s body.

Four articular processes, two superior and two inferior arise from the junction of the pedicles and laminae to articulate with the vertebrae above and below. The articulating surfaces of the four articular processes are covered with fibrocartilage and are called facets. In a typical vertebra, each superior articular process has an articular facet on its posterior surface, and each inferior articular process has an articular facet on the anterior surface. The planes of the facets vary in direction in the different regions of the vertebral column and often vary within the same vertebra. The articulations between the articular processes of the vertebral arches are referred to as zygapophyseal joints or interarticular facet joints.

The movable vertebrae, with the exception of the first and second cervical vertebrae, are similar in general structure.

Cervical vertebrae:

The first two cervical vertebrae are atypical in that they are structurally modified to join the skull. The seventh vertebra is atypical also and slightly modified to join the thoracic spine.

Atlas:

The atlas, the first cervical vertebra (C1), is a ring like structure with no body and a very short spinous process. The atlas consists of an anterior arch, a posterior arch, two lateral masses, and two transverse processes. The anterior and posterior arches extend between the lateral masses. The ring formed by the arches is divided into anterior and posterior portions by a ligament called the transverse atlantal ligament. The anterior portion of the ring receives the dens (odontoid process) of the axis, the posterior portion transmits the proximal spinal cord.

The transverse processes of the atlas are longer than those of the other cervical vertebrae, and they project laterally and slightly inferiorly from the lateral masses. Each lateral mass bears a superior and an inferior articular process. The superior processes lie in a horizontal plane, are large and deeply concave, and are shaped to articulate with the occipital condyles of the occipital bone of the cranium.

Axis:

The axis, the second cervical vertebra (C2) has a strong conical process arising from the upper surface of its body. This process, called the dens or odontoid process, is received into the anterior portion of the atlantal ring to act as the pivot or body for the atlas. At each side of the dens on the superior surface of the vertebral body are the superior articular processes, which are adapted to join with the inferior articular processes of the atlas. These joints, which differ in position and direction from the other cervical zygapophyseal joints, are clearly visualized in an AP projection if the patient is correctly positioned. The inferior articular processes of the axis have the same direction as those of the succeeding cervical vertebrae. The laminae of the axis are broad and thick. The spinous process is horizontal in position.

Seventh vertebra:

The seventh cervical vertebra (C7), termed the vertebra prominens, has a long, prominent spinous process that projects almost horizontally to the posterior. The spinous process of this vertebra is easily palpable at the posterior base of the neck.

Typical cervical vertebra:

The typical cervical vertebrae (C3-C6) have a small, transversely located, oblong body with slightly elongated anteroinferior borders. The result is anteroposterior overlapping of the bodies in the articulated column. The transverse processes of the typical cervical vertebra arise partly from the sides of the body and partly from the vertebral arch. These processes are short and wide, are perforated by the transverse foramina for the transmission of the vertebral artery and vein, and present a deep concavity on their upper surfaces for the passage of the spinal nerves. All cervical vertebrae contain three foramina: the right and left transverse foramina and vertebral foramen.

The pedicles of the typical cervical vertebra project laterally and posteriorly from the body, and their superior and inferior vertebral notches are nearly equal in depth. The laminae are narrow and thin. The spinous processes are short, have double pointed (bifid) tips, and are directed posteriorly and slightly inferiorly. Their palpable tips lie at the level of the interspace below the body of the vertebra from which they arise.

The superior and inferior articular processes are located posterior to the transverse processes at the point where the pedicles and lamina unite. Together the processes form short, thick columns of bone called articular pillars. The fibrocartilaginous articulating surfaces of the articular pillars contain facets. The zygoapophyseal facet joints of the second through seventh cervical vertebrae lie at right angles to the midsagittal plane and are clearly demonstrated in a lateral projection.

The intervertebral foramina of the cervical region are directed anteriorly at 45⁰ from the midsagittal plane of the body. The foramina are also directed at a 15⁰ inferior angle to the horizontal plane of the body. Accurate radiographic demonstration of these foramina requires a 15⁰ longitudinal angulation of the central ray and a 45⁰ medial rotation of the patient (or 45⁰ medial angulation of the central ray). A lateral projection is necessary to demonstrate the cervical zygapophyseal joints.

Thoracic vertebrae:

The bodies of the thoracic vertebrae increase in size from the first to the twelfth vertebrae. They also vary in form, with the superior thoracic bodies resembling cervical bodies and the inferior thoracic bodies resembling lumbar bodies. The bodies of the typical (third through ninth) thoracic vertebrae are approximately triangular in form. These vertebral bodies are deeper posteriorly than anteriorly, and their posterior surface is concave from side to side.

The posterolateral margins of each thoracic body have costal facets for articulation with the heads of the ribs. The body of the first thoracic vertebra presents a whole costal facet near its superior border for articulation with the head of the first rib and presents, a demifacet (half facet) on its inferior border for articulation with the head of the second rib. The bodies of the second through eighth thoracic vertebrae contain demifacets both superiorly and inferiorly. The ninth thoracic vertebra has only a superior demifacet. Finally, the tenth, eleventh, and twelfth thoracic vertebral bodies have a single whole facet at the superior margin for articulation with the eleventh and twelfth ribs.

The transverse processes of the thoracic vertebrae project obliquely, laterally, and posteriorly. With the exception of the eleventh and twelfth pairs, each process has on the anterior surface of its extremity a small concave facet for articulation with the tubercle of a rib. The laminae are broad and thick, and they overlap the subjacent lamina. The spinous processes are long. From the fifth to ninth vertebrae the spinous process project sharply inferiorly and overlap each other, but they are less vertical above and below this region. The palpable tip of each spinous process of the fifth to ninth thoracic vertebrae corresponds in position to the interspace below the vertebra from which it projects.

The zygapophyseal joints of the thoracic region angle (except the inferior articular processes of the twelfth vertebra), anteriorly approximately 15 to 20⁰ to form an angle of 70 to 75⁰ (open anteriorly) to the midsagittal plane of the body. For radiographic demonstration of the zygapophyseal joints of the thoracic region, the patient’s body must be rotated 70 to 75⁰ from the anatomic position or 15 to 20⁰ from the lateral position.

The intervertebral foramina of the thoracic region are perpendicular to the midsagittal plane of the body. These foramina are clearly demonstrated radiographically with the patient in a true lateral position. During inspiration the ribs are elevated. The arms must also be raised enough to elevate the ribs, which otherwise cross the intervertebral foramina.

Table: costal facets and demifacets

Vertebrae	Vertebral border	Facet/demifacet
T1	Superior	Whole facet
	Inferior	Demifacet
T2-T8	Superior	Demifacet
	Inferior	Demifacet
T9	Superior	Demifacet
	Inferior	None
T10-T12	Superior	Whole facet
	Inferior	None

Lumbar vertebrae:

The lumbar vertebrae have large bean shaped bodies that increases in size from the first to the fifth vertebra in this region. The lumbar bodies are deeper anteriorly than posteriorly, and their superior and inferior surfaces are flattened or slightly concave. At their posterior surface these vertebrae are flattened anteriorly to posteriorly, and they are transversely concave. The anterior and lateral surfaces are concave from the top to the buttom.

The transverse processes of lumbar vertebrae are smaller than those of the thoracic vertebrae. The superior three pairs are directed almost exactly laterally, whereas the inferior two pairs are inclined slightly superiorly. The lumbar pedicles are strong and are directed posteriorly; the laminae are thick. The spinous processes are large, thick and blunt, and they have an almost horizontal projection posteriorly. The palpable tip of each spinous interspace blow the vertebra from which it projects. The mammillary process is a smoothly rounded projection on the back of each superior articular process. The accessory process is at the back of the root of the transverse process.

The body of the fifth lumbar segment is considerably deeper in front than behind, which gives it a wedge shape that adapts it for articulation with the sacrum. The intervertebral disk of this joint is also more wedge shaped than the disks in the interspaces above the lumbar region. The spinous process of the fifth lumbar vertebra is smaller and shorter, and the transverse processes are much thicker than those of the upper lumbar vertebrae.

The laminae lie posterior to the pedicles and transverse processes. The part of the lamina between the superior and inferior articular processes is called the pars interarticularis.

The zygapophyseal joints of the lumbar region are inclined posteriorly from the coronal plane, forming an average angle (open posteriorly) of 30-60⁰ to the midsagittal plane of the body.

The average angle increases from cephalad to caudad with L1-L2 at 15⁰, L2-L3 at 30⁰, and L3-L4 through L5-S1 at 45⁰. A significant number of upper joints have no angle, and a significant number of lower joints have an angle of 60⁰ or more. Although the customary 45⁰ oblique body position will demonstrate the majority of clinically significant lumbar zygopophyseal joints (L3- through S1), upto 25% OF L1-L2 and L2-L3 joints will be demonstrated on an AP projection and a small percentage of L4-L5 and L5-S1 joints will be seen on a lateral projection.

The intervertebral foramina of the lumbar region are situated at right angles to the midsagittal plane of the body, except the fifth, which turns slightly anteriorly. The superior four pairs of foramina are demonstrated radiographically with the patient in a true lateral position; the last pair requires slight obliquity of the body.

Spondylolysis is an acquired bony defect occurring in the pars interarticularis, the area of the lamina between the two articular processes. The defect may occur on one or both sides of the vertebra, resulting in a condition termed spondylolisthesis. This condition is characterized by the anterior displacement of one vertebra over another, generally the fifthe lumbar over the sacrum. Spondylolisthesis almost exclusively involves the lumbar spine.

Spondylolisthesis is of radiologic importance because oblique position radiographs demonstrate the “neck” are of the “Scottie dog” (i.e., the pars interarticularis).

Sacrum:

The sacrum is formed by fusion of the five sacral vertebral segments into a curved, triangular bone. The sacrum is wedged between the iliac bones of the pelvis, with its broad base directed obliquely, superiorly and anteriorly and its apex directed posteriorly and inferiorly. Although the size and degree of curvature of the sacrum vary considerably in different patients, the bone is normally longer, narrower, more evenly curved, and more vertical in position in males than in females. The female sacrum is more acute curved, with its greatest curvature in the lower half of the bone; it also lies in a more oblique plane, which results in a sharper angle at the junction of the lumbar and pelvic curves.

The superior portion of the first sacral segment remains distinct and resembles the vertebrae of the lumbar region. The superior surface of the base of the sacrum corresponds in size and shape to the inferior surface of the last lumbar segment, with which it articulates to form the lumbosacral junction. The concavities on the upper surface of the pedicles of the first sacral segment and the corresponding concavities on the lower surface of the pedicles of the last lumbar segment form the last pair of intervertebral foramina. The superior articular processes of the first sacral segment articulate with the inferior articular processes of the last lumbar vertebra to form the last pair of zygapophyseal joints.

At its superior anterior margin the base of the sacrum has a prominent ridge termed the sacral promontory. Directly behind the bodies of the sacral segments is the sacral canal, which is the continuation of the vertebral canal. The sacral canal is contained within the bone and transmits the sacral nerves. The anterior and posterior walls of the sacral canal are each perforated by four pairs of pelvic sacral foramina for the passage of the sacral nerves and blood vessels.

On each side of the sacral base is a large, winglike lateral mass called the ala. At the superoanterior part of the lateral surface of each ala is the auricular surface, a large articular process for articulation with similarly shaped processes on the iliac bones of the pelvis.

The inferior surface of the apex of the sacrum has an oval facet for articulation with the coccyx and the sacral cornua, two processes that project inferiorly from the posterolateral aspect of the last sacral segment to join the coccygeal cornua.

Coccyx:

The coccyx is composed of three to five (usually four) rudimentary vertebrae that have a tendency to fuse into one bone in the adult. The coccyx diminished in size from its base inferiorly to its apex. From its articulation with the sacrum, it curves inferiorly and anteriorly, often deviating from the midline of the body. The coccygeal cornua project superiorly from the posterolateral aspect of the first coccygeal segment to join the sacral cornua.

Vertebral articulations:

The vertebral articulations consist of two types of joints:

1.     Intervertebral joints, which are between the two vertebral bodies and are cartilaginous symphysis joints that permit only slight movement of individual vertebrae but considerable motility for the column as a whole, and

2.     Zygapophyseal joints, which are between the articulation processes of the vertebral arches and are synovial gliding joints that permit free movement.

The movements permitted in the vertebral column by the combined action of the joints are flexion, extension, lateral flexion and rotation.

The articulations between the atlas and the occipital bone are synovial ellipsoidal joints and are called the atlanto-occipital articulations. The anterior arch of the atlas rotates about the dens of the axis to form the atlantoaxial joint, which is both a synovial gliding articulation and a synovial pivot articulation.

In the thoracic region, the heads of the ribs articulate with the bodies of the vertebrae to form the costovertebral joints, which are synovial gliding articulations. The tubercles of the ribs and transverse processes of the thoracic vertebrae articulate to form costotransverse joints, which are also synovial gliding articulations.

Table: Structural classification of Joints of the vertebral column:

Joint	Tissue	Type	Movement
Atlanto-occipital	Synovial	Ellipsoidal	Freely movable
Atlantoaxial
Lateral (2)	Synovial	Gliding	Freely movable
Medial (1-dens)	Synovial	Pivot	Freely movable
Intervertebral	Cartilaginous	Symphysis	Slightly movable
Zygapophyseal	Synovial	Gliding	Freely movable
Costovertebral	Synovial	Gliding	Freely movable
Costotransverse	Synovial	Gliding	Freely movable

Pathology:

1.     Ankylosing spondylitis: rheumatoid arthritis variant involving the sacroiliac joints and spine

2.     Fracture: disruption in the continuity of bone

3.     Clay shoveler’s: avulsion fracture of the spinous process in the lower cervical and upper thoracic

4.     Compression: fracture that causes compaction of bone and a decrease in length or width

5.     Hangman’s: fracture of the anterior arch of C2 due to hyperextension

6.     Jefferson: comminuted fracture of the ring of C1

7.     Herniated Nucleus Pulposus: rupture or prolapse of the nucleus pulposus in the spinal cord

8.     Kyphosis: abnormally increased convexity in the thoracic curvature

9.     Lordosis: abnormally increased concavity of the cervical and lumbar spine

10.                        Metastases: transfer of a cancerous lesion from one area to another

11.                        Osteoarthritis or Degenerative Joint Disease: form of arthritis marked by progressive cartilage deterioration in synovial joints and vertebrae

12.                        Osteopetrosis: increased density of atypically soft bone

13.                        Osteoporosis: loss of bone density

14.                        Paget’s disease: thick, soft bone marked by bowing and fractures

15.                        Scheuermann’s Disease or Adolescent Kyphosis: kyphosis with onset in adolescence

16.                        Scoliosis: lateral deviation of the spine with possible vertebral rotation

17.                        Spina bifida: failure of the posterior encasement of the spinal cord to close

18.                        Spondylolisthesis: forward displacement of a vertebra over a lower vertebra, usually L5-S1

19.                        Spondylosis: breaking down of the vertebra

20.                        Subluxation: incomplete or partial dislocation

21.                        Tumor: new tissue growth where cell proliferation is uncontrolled

22.                        Multiple myeloma: malignant neoplasm of plasma cells involving the bone marrow and causing destruction of the bone

Bony Thorax:

The bony thorax supports the walls of the pleural cavity and diaphragm used in respiration. The thorax is constructed so that the volume of the thoracic cavity can be varied during respiration. The thorax also serves to protect the heart and lungs. The bony thorax is formed by the sternum, 12 pairs of ribs and 12 thoracic vertebrae. The bony thorax protects the heart and lungs. Conical in shape, the bony thorax is narrower above than below, more wide than deep, and longer posteriorly than anteriorly.

Sternum:

The sternum, or breastbone is directed anteriorly and inferiorly and is centered over the midline of the anterior thorax. A narrow, flat bone about 15 cm in length, the sternum consists of three parts: manubrium, body and xiphoid process. The sternum supports the clavicles at the superior manubrial angles and provides attachment to the costal cartilages of the first seven pairs of ribs at the lateral borders.

The manubrium, the superior portion of the sternum, is quadrilateral in shape and is the widest portion of the sternum. At its center, the superior border of the manubrium has an easily, palpable concavity termed the jugular notch. In the upright position, the jugular notch of the average person lies anterior to the interspace between the second and third thoracic vertebrae. The manubrium slants laterally and posteriorly on each side of the jugular notch and an oval articular facet called the clavicular notch articulates with the sternal extremity of the clavicle. On the lateral borders of the manubrium, immediately below the articular notches for the clavicles, are shallow depressions for the attachment of the cartilages of the first pair of ribs.

The body is the longest part of the sternum and is joined to the manubrium at the sternal angle, an obtuse angle that lies at the level of the junction of the second costal cartilage. Both the manubrium and the body contribute to the attachment of the second costal cartilage. The succeeding five pairs of costal cartilages are attached to the lateral borders of the body. The sternal angle is palpable; in the normally formed thorax, it lies anterior to the interspace between the fourth and fifth thoracic vertebrae when the body is in upright.

The xiphoid process, the distal and smallest part of the sternum, is cartilaginous in early life and partially or completely ossifies, particularly the superior portion, in later life. The xiphoid process is variable in shape and often deviates from the midline of the body. In the normal thorax, the xiphoid process lies over the tenth thoracic vertebra and serves as a useful bony landmark for locating the superior portion of the liver and the inferior border of the heart.

Ribs:

The 12 pairs of ribs are numbered consecutively from superiorly to inferiorly. The rib number corresponds to the thoracic vertebra to which it attaches. Each rib is a long, narrow, curved bone with an anteriorly attached piece of hyaline cartilage, the costal cartilage. The costal cartilages of the first through seventh ribs attach directly to the sternum. The costal cartilages of the eighth through tenth ribs attach to the costal cartilage of the seventh rib. The ribs are situated in an oblique plane slanting anteriorly and inferiorly so that their anterior ends lie 3 to 5” below the level of their vertebral ends. The degree of obliquity gradually increases from the first to the ninth rib and then decreases to the twelfth rib. The first seven ribs are called true ribs because they attach directly to the sternum. Ribs 8 to 12 are called false ribs because they do not attach directly to the sternum. The last two ribs (eleventh and twelfth ribs) are often called floating ribs because they are attached only to the vertebrae. The spaces between the ribs are referred to as the intercostal spaces.

The number of ribs may be increased by the presence of cervical or lumbar ribs, or both. Cervical ribs articulate with the C7 vertebra but rarely attach to the sternum. Cervical ribs may be free or articulate or fuse with the first rib. Lumbar ribs are less common than cervical ribs. Lumbar ribs can lend confusion to images. They can confirm the identification of the vertebral level or they can be erroneously interpreted as a fractured transverse process of the L1 vertebra.

The ribs vary in breath and length. The first rib is the shortest and broadest; the breath gradually decreases to the twelfth rib, the narrowest rib. The length increase from the first to the seventh rib and then gradually decrease to the twelfth rib.

A typical rib consists of a head, a flattened neck, a tubercle and a body. The ribs have facets on their heads for articulation with the vertebrae. On some ribs the facet is divided into superior and inferior portions for articulation with demifacets on the vertebral bodies. The tubercle also contains a facet for articulation with the transverse process of the vertebra. The eleventh and twelfth ribs do not have a neck or tubercular facets. The two ends of a rib are termed the vertebral end and the sternal end.

From the point of articulation with the vertebral body, the rib projects posteriorly at an oblique angle to the point of articulation with the transverse process. The rib turns laterally to the angle of the body, where the bone arches anteriorly, medially and inferiorly in an oblique plane. Located along the inferior and internal border of each rib is the costal groove, which contains costal arteries, veins, and nerves. Trauma to the ribs can damage these neurovascular structures, causing pain and hemorrhage.

Bony Thorax articulations:

The sternoclavicular (SC) joints are the only points of articulation between the upper limbs and the trunk. Formed by the articulation between the sternal extremity of the clavicles and the clavicular notches of the manubrium, these synovial gliding joints permit free movement (the gliding of one surface on the other). A circular disk of fibrocartilage is interposed between the articular ends of the bones in each joint, and the joints are enclosed in articular capsules.

Table: Structural classification of joints of the bony thorax:

Joint	Tissue	Type	Movement
Sternoclavicular	Synovial	Gliding	Freely movable
Costovertebral:
1st through 12th ribs	Synovial	Gliding	Freely movable
Costotransverse:
1st through 10th ribs	Synovial	Gliding	Freely movable
Costochondral:
1st through 10th ribs	Cartilaginous	Synchondroses	Immovable
Sternocostal:
First rib	Cartilaginous	Synchondroses	Immovable
2nd through 7th ribs	Synovial	Gliding	Freely movable
Interchondral:
6th through 9th ribs	Synovial	Gliding	Freely movable
9th through 10th ribs	Fibrous	Syndesmoses	Slightly movable
Manubriosternal	Cartilaginous	Symphysis	Slightly movable
Xiphisternal	Cartilaginous	Synchondroses	Immovable

Posteriorly, the head of a rib is closely bound to the demifacets of two adjacent vertebral bodies to form a synovial gliding articulation called the costovertebral joint. The first, tenth, eleventh, and twelfth ribs each articulate with only one vertebral body.

The tubercle of a rib articulates with the anterior surface of the transverse process of the lower vertebra at the costotransverse joint, and the head of the rib articulates at the costovertebral joint. The head of the rib also articulates with the body of the same vertebra and articulates with the vertebra directly above. The costotransverse articulation is also a synovial gliding articulation. The articulations between the tubercles of the ribs and the transverse processes of the vertebrae permit only superior and inferior movements of the first six pairs. Greater freedom of movement is permitted in the succeeding four pairs.

Costochondral articulattions are found between the anterior extremities of the ribs and the costal cartilages. These articulations are cartilaginous synchondrosis and allow no movement. The articulations between the costal cartilages of the true ribs and the sternum are called sternocostal joints. The first pair of ribs, rigidly attached to the sternum, form the first sternocostal joint. This is a cartilaginous synchondrosis type of joint, which allows no movement. The second through seventh sternocostal joints are considered synovial gliding joints and are freely movable. Interchondral joints are found between the costal cartilages of the sixth and seventh, seventh and eighth and eighth and ninth ribs. These interchondral joints are synovial gliding articulations. The interchondral articulation between the ninth and tenth ribs is fibrous syndesmosis and only slightly movable.

The manubriosternal joint is cartilaginous symphysis and the xiphisternal joints are cartilaginous synchondrosis joints that allow little or no movement.

Pathology:

1.     Fracture: disruption of the continuity of bone

2.     Metastases: transfer of a cancerous lesion from one area to another

3.     Osteomyelitis: inflammation of bone due to pyogenic infection

4.     Osteopetrosis: increased density of atypically soft tissue

5.     Osteoporosis: loss of bone density

6.     Paget’s disease: thick, soft bone marked by bowing and fractures

7.     Tumor: new tissue growth where cell proliferation is uncontrolled

8.     Chondrosarcoma: malignant tumor arising from cartilage cells

9.     Multiple myeloma: malignant neoplasm of plasma cells involving the bone marrow and causing destruction of the bone

Thoracic viscera:

Body habitus:

The general shape of the human body or the body habitus, determines the size, shape, position and movement of the internal organs.

Thoracic cavity:

The thoracic cavity is bounded by the walls of the thorax and extends from the superior thoracic aperture, where structures enter the thorax, to the inferior thoracic aperture. The diaphragm separates the thoracic cavity from the abdominal cavity. The anatomic structures that pass from the thorax to the abdomen go through openings in the diaphragm.

The thoracic cavity contains the lungs and heart; organs of the respiratory, cardiovascular and lymphatic systems; the inferior portion of the oesophagus; and the thymus gland. Within the cavity are three separate chambers; a single pericardial cavity and the right and left pleural cavities. These cavities are lined by shiny, slippery, and delicate serous membranes. The space between the two pleural cavities is called the mediastinum. This area contains all the thoracic structures except the lungs and pleurae.

Respiratory system:

The respiratory system consists of the pharynx, trachea, bronchi and two lungs. The air passages of these organs communicate with the exterior through the pharynx, mouth, and nose.

Trachea:

The trachea is a fibrous, muscular tube with 16 to 20 C-shaped cartilaginous rings embedded in its walls for greater rigidity. It measures approximately half inch in diameter and four and half inch in length and its posterior aspect is flat. The cartilaginous rings are incomplete posteriorly and extend around the anterior two thirds of the tube. The trachea lies in the midline of the body, anterior to the oesophagus in the neck. However, in the thorax, the trachea is shifted slightly to the right of the midline as a result of the arching of the aorta. The trachea follows the curve of the vertebral column and extends from its junction with the larynx at the level of the sixth cervical vertebra inferiorly through the mediastinum to about the level of the space between the fourth and fifth thoracic vertebrae. The last tracheal cartilage is elongated and has a hook like process, the carina, which extends posteriorly on its inferior surface. At the carina, the trachea divides or bifurcates into two lesser tubes, the primary bronchi. One of these bronchi enters the right lung and the other enters the left lung.

The primary bronchi slant obliquely inferiorly to their entrance into the lungs, where they branch out to form the right and left bronchial branches. The right primary bronchus is shorter, wider, and more vertical than the left primary bronchus. Because of the more vertical position and greater diameter of the right main bronchus, foreign bodies entering the trachea are more likely to pass into the right bronchus than the left bronchus.

After entering the lung, each primary bronchus divides, sending branches to each lobe of the lung: three to the right lung and two to the left lung. These secondary bronchi further divide and decrease in caliber. The bronchi continue dividing into tertiary bronchi, then to smaller bronchioles, and end in minute tubes called the terminal bronchioles. The extensive branching of the trachea is commonly referred to as the bronchial tree because it resembles a tree trunk.

Alveoli:

The terminal bronchioles communicate with alveolar ducts. Each duct ends in several alveolar sacs. The walls of the alveolar sacs are lined with a alveoli. Each lung contains millions of alveoli. Oxygen and carbon dioxide are exchanged by diffusion within the walls of the alveoli.

Lungs:

The lungs are the organs of respiration. They comprise the mechanism for introducing oxygen into the blood and removing carbon dioxide from the blood. The lungs are composed of a light, spongy, highly elastic substance, the parenchyma, and they are covered by a layer of a serous membrane. Each lung presents a rounded apex that reaches above the level of the clavicles into the root of the neck and a broad base that resting on the obliquely placed diaphragm, reaches lower in back and at the sides than in front. The right lung is about 2.5 cm shorter than left lung because of the large space occupied by the liver, and it is broader than the left lung because of the position of the heart. The lateral surface of each lung conforms with the shape of the chest wall. The inferior surface of the lung is concave, fitting over the diaphragm, and the lateral margins are thin. During respiration the lungs move inferiorly for inspiration and superiorly for expiration. During inspiration the lateral margins descend into the deep recesses of the parietal pleura. In radiology, this recess is called the costophrenic angle. The mediastinal surface is concave with a depression, called the hilum, that accommodates the bronchi, pulmonary blood vessels, lymph vessels and nerves. The inferior mediastinal surface of the left lung contains a concavity called the cardiac notch. This notch conforms to the shape of the heart.

Each lung is enclosed in a double walled serous membrance sac called the pleura. The inner layer of the pleural sac called the visceral pleura, closely adheres to the surface of the lung, extends into the interlobar fissures, and is contiguous with the outer layer at the hilum. The outer layer called the parietal pleura lines the wall of the thoracic cavity occupied by the lung and closely adheres to the upper surface of the diaphragm. The two layers are moistened by serous fluid so that they move easily on each other. Thus the serous fluid prevents friction between the lungs and chest walls during respiration. The space between the two pleural walls is called the pleural cavity. Although the space is termed a cavity, the layers are actually in close contact.

Each lung is divided into lobes by deep fissures. The fissures lie in an oblique plane inferiorly and anteriorly from above, so that the lobes overlap each other in the AP direction. The oblique fissures divide the lungs into superior and inferior lobes. The superior lobes lie above and are anterior to the inferior lobes. The right superior lobe is further divided by a horizontal fissure, creating a right middle lobe. The left lung has no horizontal fissure and thus no middle lobe. The portion of the left lobe that corresponds in position to the right middle lobe is called the lingula. The lingual is a tongue shaped process on the anteromedial border of the left lung. It fills the space between the chest wall and the heart.

Each of the five lobes divides into bronchopulmonary segments and subdivides into smaller units called primary lobules. The primary lobule is the anatomic unit of lung structure and consists of a terminal bronchiole with its expanded alveolar duct and alveolar sac.

Mediastinum:

The mediastinum is the area of the thorax bounded by the sternum anteriorly, the spine posteriorly, and the lungs laterally. The structures associated with the mediastinum are as follows:

1.     Heart

2.     Great vessels

3.     Trachea

4.     Esophagus

5.     Thymus

6.     Lymphatics

7.     Nerves

8.     Fibrous tissue

9.     Fat

The esophagus is the part of the digestive canal that connects the pharynx with the stomach. It is a narrow, musculomembranous tube about 9” in length. Following the curves of the vertebral column, the oesophagus descends through the posterior part of the mediastinum and then runs anteriorly to pass through the esophageal hiatus of the diaphragm.

The esophagus lies just in front of the vertebral column, with its anterior surface in close relation to the trachea, aortic arch, and heart. This makes the esophagus valuable in certain heart examinations. When the esophagus is filled with barium sulphate, the posterior border of the heart and aorta are outlined well in lateral and oblique projections. Frontal, oblique, and lateral images are often used in examinations of the esophagus.

The thymus gland is the primary control organ of the lymphatic system. It is responsible for producing the hormone thymosin, which plays a critical role in the development and maturation of the immune system. The thymus consists of two pyramid shaped lobes that lies in the lower neck and superior mediastinum, anterior to the trachea and great vessels of the heart and posterior to the manubrium. The thymus reaches its maximum size at puberty and then gradually undergoes atrophy until it almost disappears.

In older individuals, lymphatic tissue is replaced by fat. At its maximum development the thymus rests on the pericardium and reaches as high as the thyroid gland. When the thymus is enlarged in infants and young children, it can press on the retrothymic organs, displacing them posteriorly and causing respiratory disturbances. A radiographic examination may be made in both AP and lateral projections

Pathology:

1.     Aspiration/ foreign body: inspiration of a foreign material into the airway

2.     Atelectasis: a collapse of all or part of the lung

3.     Bronchiectasis: chronic dilatation of the bronchi and bronchioles associated with secondary infection

4.     Bronchitis: inflammation of the bronchi

5.     Chronic obstructive pulmonary disease: chronic condition of persistent obstruction of bronchial airflow

6.     Cystic fibrosis: disorder associated with widespread dysfunction of the exocrine glands, abnormal secretion of sweat and saliva, and accumulation of thick mucus in the lungs

7.     Emphysema: destructive and obstructive airway changes leading to an increased volume or air in the lungs

8.     Epiglottis: inflammation of the epiglottis

9.     Fungal disease: inflammation of the lung caused by a fungal organism

10.                        Histoplasmosis: infection caused by the yeast like organism Histoplasma capsulatum

11.                        Granulomatous disease: condition of the lung marked by formation of granulomas

12.                        Sarcoidosis: condition of unknown origin often associated with pulmonary fibrosis

13.                        Tuberculosis: chronic infection of the lung due to the tubercle bacillus

14.                        Hyaline membrane disease or respiratory distress syndrome: underaeration of the lungs due to a lack of surfactant

15.                        Metastases: transfer of a cancerous lesion from one area to another

16.                        Pleural effusion: collection of fluid in the pleural cavity

17.                        Pneumoconiosis: lung diseases resulting from the inhalation of industrial substances

18.                        Anthracosis or coal miner’s lung or black lung: inflammation caused by inhalation of coal dust (anthracite)

19.                        Asbestosis: inflammation caused by inhalation of asbestos

20.                        Silicosis: inflammation caused by inhalation of silicon dioxide

21.                        Pneumonia: acute infection in the lung parenchyma

22.                        Aspiration: pneumonia caused by aspiration of foreign particles

23.                        Interstitial or viral or pneumonitis: pneumonia caused by a virus and involving the alveolar walls and interstitial structures

24.                        Lobar or bacterial: pneumonia involving the alveoli of an entire lobe without involving the bronchi

25.                        Lobular or bronchopneumonia: pneumonia involving the bronchi and scattered throughout the lung

26. Pneumothorax: accumulation of air in the pleural cavity resulting in collapse of the lung

27. Pulmonary edema: replacement of air with fluid in the lung interstitium and alveoli

28. Tumor: new tissue growth where cell proliferation is uncontrolled