Back and Thorax Exam

Regional Characteristics of Vertebrae

• Cervical vertebrae:
  • Form the skeleton of the neck
  • Smallest of the 24 movable vertebrae
  • Located between the cranium and thoracic vertebrae
  • Smaller size reflects the fact that they bear less weight than the larger inferior vertebrae
  • Greatest range and variety of movement of all vertebral regions
• Distinctive features of cervical vertebrae:
  • Vertebral body: small and wider from side to side than anteroposteriorly
  • Superior surface concave with uncus of body (uncinate process)
  • Inferior surface convex
  • Transverse foramen: most distinctive feature of each cervical vertebra, found in the transverse process
  • Articular processes: superior facets directed superoposteriorly; inferior facets directed infero-anteriorly
  • Spinous process: short (C3-C5) and bifid (C3-C6); process of C6 long, that of C7 longer (vertebra prominens)

Atlanto-Axial Joints

• Formed between the atlas (C1) and axis (C2)
• Permit the head to be turned side to side (the "NO" movement)
• Cranial and C1 rotate on C2, with the dens as a pivot
• Three atlanto-axial articulations:
  • Two lateral atlanto-axial joints: between interior facets of lateral masses of C1 and superior facets of C2
  • One median atlanto-axial joint: between the dens (C2) and anterior arch of Atlas (C1)

Vertebral Column

• Four curvatures of the adult vertebral column: cervical, thoracic, lumbar, and sacral
• Primary curvatures: thoracic and sacral kyphoses, developed during the fetal period
• Secondary curvatures: cervical and lumbar lordoses, acquired in relation to the erect human posture
• Curvatures provide resilience, flexibility, and shock-absorbance to the axial skeleton

Vascularity and Nerve Supply of Vertebral Column

• Spinal branches of the major cervical and segmental arteries supply the vertebral column
• Venous drainage: internal and external vertebral venous plexuses collect blood from the vertebrae and drain into the vertebral veins of the neck and segmental veins of the trunk
• Nerve supply: recurrent meningeal branches of the spinal nerves supply most bone, IV discs, and ligaments as well as the meninges of the spinal cord

Ossification of Vertebrae

• Begins around the 8th week at the end of the embryonic period
• Three primary ossification centers develop in cartilaginous vertebrae:
  • Endrochondral centrum
  • Two perichondral centers in each half of the neural arch
• Ossification continues through fetal period
• At birth, vertebra consists of three bony parts united by hyaline cartilage
• Inferior sacral and coccygeal vertebrae still cartilaginous; ossify during infancy

Intrinsic Back Muscles

• The intrinsic back muscles consist of two groups: the major deep layer and the minor deep layer.
• The major deep layer includes the transversospinalis muscle group, which consists of semispinalis, multifidus, and rotatores.
  • Semispinalis:
    • Originates from transverse processes of vertebrae
    • Passes to spinous processes of more superior vertebrae
    • Divided into three parts: semispinalis capitis, semispinalis thoracis, and semispinalis cervicis
    • Semispinalis capitis forms the longitudinal bulge in the back of the neck
  • Multifidus:
    • Originates from posterior sacrum, posterior superior iliac spine, and transverse processes of vertebrae
    • Passes to spinous processes of more superior vertebrae
    • Thickest in the lumbar region
    • Stabilizes vertebrae during local movements
  • Rotatores:
    • Originates from transverse processes of vertebrae
    • Passes to spinous processes of more superior vertebrae
    • Best developed in the thoracic region
    • Acts as stabilizers
• The minor deep layer includes interspinales, intertransversarii, and levatores costarum.
  • Interspinales:
    • Aids in extension and rotation of vertebral column
  • Intertransversarii:
    • Aids in lateral flexion of vertebral column
    • Acts bilaterally to stabilize vertebral column
  • Levatores costarum:
    • Elevates ribs and aids in respiration
    • Assists in lateral flexion of vertebral column

Surface Anatomy of the Back

• The surface anatomy of the back includes the following landmarks:
  • Nuchal groove
  • Vertebra prominens (C7)
  • Posterior median furrow
  • Intergluteal cleft
  • Erector spinae
  • Trapezius
  • Rhomboids
  • Latissimus dorsi
  • Median borders of scapulae
  • Dimples overlying PSIS
  • Site of sacrum

Suboccipital and Deep Neck Muscles

• The suboccipital region includes four small muscles:
  • Rectus capitis posterior major
  • Rectus capitis posterior minor
  • Obliquus capitis superior
  • Obliquus capitis inferior
• These muscles are mainly postural muscles, but they also act to produce movement of the head.
• The suboccipital muscles act on the head directly or indirectly by extending it on vertebra C1 and rotating it on C1 and C2.

Suboccipital Triangle

• The suboccipital triangle is bounded by:
  • Superomedial boundary: posterior atlanto-occipital membrane
  • Superolateral boundary: rectus capitis posterior major
  • Inferolateral boundary: obliquus capitis inferior
  • Floor: posterior arch of vertebra C1 (atlas)
  • Roof: semispinalis capitis
  • Contents: vertebral artery and suboccipital nerve

Principal Muscles Producing Movement of Atlanto-Occipital Joints

• Flexion:
  • Longus capitis
  • Rectus capitis anterior
  • Anterior fibers of sternocleidomastoid
  • Suprahyoid and infrahyoid muscles
• Extension:
  • Rectus capitis posterior major and minor
  • Obliquus capitis superior
  • Longissimus capitis
  • Splenius capitis
• Rotation:
  • Obliquus capitis inferior
  • Rectus capitis posterior major and minor
  • Longissimus capitis
  • Splenius capitis

Nerves of the Posterior Cervical Region

• The suboccipital nerve is a branch of the posterior ramus of spinal nerve C1.
• The greater occipital nerve is a branch of the posterior ramus of spinal nerve C2.
• The lesser occipital nerve is a branch of the anterior rami of spinal nerves C2-C3.
• The posterior rami of spinal nerves C3-C7 innervate the skin and muscles of the back and neck.

The Spinal Cord

• The spinal cord is a major reflex center and conduction pathway between the body and brain.

• It is protected by the vertebrae, their ligaments and muscles, the spinal meninges, and the cerebrospinal fluid.

• The spinal cord occupies the superior two-thirds of the vertebral canal in adults.

• It is a continuation of the medulla oblongata and extends from the foramen magnum in the occipital bone to the level of the L1 or L2 vertebra.

• The spinal cord has two enlargements: the cervical enlargement and the lumbosacral enlargement.

• The conus medullaris is the inferior, tapering end of the spinal cord, and it ends at the level of the L1 or L2 vertebra.

• The cauda equina is the inferior continuation of the spinal nerve roots caudal to the termination of the spinal cord.### Arteries of Spinal Cord and Nerve Roots

• The anterior spinal artery runs inferiorly in the anterior median fissure and is formed by the union of branches of the vertebral arteries.

• Sulcal arteries arise from the anterior spinal artery and enter the spinal cord through the anterior median fissure, supplying approximately two-thirds of the cross-section.

Posterior Spinal Arteries

• Each posterior spinal artery is a branch of either the vertebral artery or the posteroinferior cerebellar artery.
• The posterior spinal arteries commonly form anastomosing channels in the pia mater.

Blood Supply to the Spinal Cord

• The anterior and posterior spinal arteries can supply only the short superior part of the spinal cord.
• Circulation to much of the spinal cord depends on segmental medullary and radicular arteries running along the spinal nerve roots.

Segmental Medullary Arteries

• The anterior and posterior segmental medullary arteries are derived from spinal branches of the ascending cervical, deep cervical, vertebral, posterior intercostal, and lumbar arteries.
• These arteries occur mainly in association with the cervical and lumbosacral enlargements, in regions where a good blood supply is needed.

The Great Anterior Segmental Medullary Artery

• The great anterior segmental medullary artery is on the left side in about 65% of people and reinforces the circulation to two-thirds of the spinal cord, including the lumbosacral enlargement.
• This artery, much larger than the other segmental medullary arteries, usually arises via a spinal branch from an inferior intercostal or upper lumbar artery and enters the vertebral canal through the IV foramen at the lower thoracic or upper lumbar level.

Radicular Arteries

• The posterior and anterior roots of the spinal nerves and their coverings are supplied by posterior and anterior radicular arteries, which run along the nerve roots.
• The radicular arteries do not reach the posterior, anterior, or spinal arteries, but are replaced by segmental medullary arteries at irregular levels.

###Thorax Anatomy

• The thorax, also known as the chest, is the part of the body between the neck and abdomen, broadest superiorly due to the presence of the pectoral girdle, pectoral and scapular muscles, and female breasts.

###Thoracic Cavity

• The thoracic cavity has the shape of a truncated cone, narrowest superiorly and increasing inferiorly.
• The thoracic cavity is divided into three major spaces: the central compartment or mediastinum (thoracic viscera except for lungs), right and left pulmonary cavities (housing the lungs).
• The floor of the thoracic cavity is the diaphragm.

###Thoracic Wall/Thoracic Cage

• The thoracic wall includes the thoracic cage, muscles that extend between the ribs, skin, subcutaneous tissue, muscles, and fascia covering the anterolateral aspect.
• Functions of the thoracic cage:
  • Protect vital thoracic and abdominal organs from external forces.
  • Resist the negative internal pressures generated by the elastic recoil of the lungs and inspiratory movements.
  • Provide attachment for and support the weight of the upper limbs.
  • Provide anchoring attachment of many muscles that move and maintain the position of the upper limbs relative to the trunk.
  • Provide attachments for muscles of the abdomen, neck, back, and respiration.

###Thoracic Skeleton

• The thoracic skeleton includes 12 pairs of ribs and associated costal cartilages, 12 thoracic vertebrae, and intervertebral discs interposed between them, and the sternum.

###Ribs

• Ribs are curved, flat bones that form most of the thoracic cage.
• Each rib has a spongy interior containing bone marrow.
• There are three types of ribs.

###Surface Anatomy of the Thoracic Wall

• Clavicles lie subcutaneously, forming bony ridges at the junction of the thorax and neck.
• Clavicles demarcate the superior division between zones of lymphatic drainage (above clavicles inferior jugular lymph nodes; below the clavicles axillary lymph nodes).
• Sternum and jugular notch (at the inferior border of T2).
• Sternal angle: level of 2nd pair of costal cartilages.

###Vertebral Levels of Sternum and Transverse Thoracic Plane

• Anterior median (midsternal) line (AML) indicates the intersection of the median plane with the anterior thoracic wall.
• Midclavicular line (MCL) passes through the midpoint of the clavicle, parallel to the AML.
• Anterior axillary line (AAL) runs vertically along the anterior axillary fold formed by the inferolateral border of the pectoralis major as it spans from the thoracic cage to the humerus in the arm.
• Midaxillary line (MAL) runs from the apex (deepest part) of the axillary fossa (armpit), parallel to the AAL.
• Posterior axillary line (PAL), also parallel to the AAL, is drawn vertically along the posterior axillary fold formed by the latissimus dorsi and teres major muscles as they span from the back to the humerus.
• Posterior median (midvertebral) line (PML) is a vertical line along the tips of the spinous processes of the vertebrae.

###Lymphatic Drainage of the Thoracic Wall

• Most lymph from the medial breast quadrants drains to the parasternal lymph nodes or to the opposite breast, whereas lymph from the inferior quadrants may pass deeply to abdominal lymph nodes (subdiaphragmatic inferior phrenic lymph nodes).

###Lymphatic Drainage of the Lungs

• The pulmonary lymphatic plexuses communicate freely.
• The superficial subpleural lymphatic plexus lies deep to the visceral pleura and drains the lung parenchyma (tissue) and visceral pleura.
• Lymphatic vessels from this superficial plexus drain into the bronchopulmonary lymph nodes (hilar lymph nodes) in the region of the lung hilum.

###Nerves of the Lungs and Pleura

• Derived from the pulmonary plexuses anterior and mainly posterior to the roots of the lungs.
• Contain parasympathetic fibers:
  • Motor to the smooth muscle of the bronchial tree (bronchoconstrictor).
  • Inhibitory to the pulmonary vessels (vasodilator).
  • Secretory to the glands of the bronchial tree (secretomotor).
• Sympathetic fibers:
  • Inhibitory to the bronchial muscle (bronchodilator).
  • Motor to the pulmonary vessels (vasoconstrictor).
  • Inhibitory to the alveolar glands of the bronchial tree—type II secretory epithelial cells of the alveoli.
• Visceral afferent fibers:
  • Reflexive (conducting subconscious sensations associated with reflexes that control function).
  • Nociceptive (conducting pain impulses generated in response to painful or injurious stimuli, such as chemical irritants, ischemia, or excessive stretch).

###Diaphragm

• Crura of the diaphragm: musculotendinous bands that arise from the anterior surfaces of the bodies of the superior three lumbar vertebrae, the anterior longitudinal ligament, and the IV discs.
• Esophageal hiatus is a formation of the right crus.
• The right and left crura and the fibrous medial arcuate ligament form the Aortic hiatus.
• Diaphragm is also attached on each side to the medial and lateral arcuate ligaments.

The Mediastinum

• The mediastinum is the middle septum that occupies the space between the two pulmonary cavities and is the central compartment of the thoracic cavity.
• It is covered on each side by mediastinal pleura and contains all of the thoracic viscera except for the lungs.
• The mediastinum extends from the superior thoracic aperture to the diaphragm and from the sternum and costal cartilages to the thoracic vertebrae.
• It is a highly mobile area in living people.

Divisions of the Mediastinum

• The mediastinum is divided into superior and inferior parts.
• The superior mediastinum extends from the superior thoracic aperture to the horizontal plane that includes the sternal angle anteriorly and the junction of T4 and T5 vertebrae posteriorly.
• The inferior mediastinum is between the transverse thoracic plane and the diaphragm.
• The inferior mediastinum is further subdivided into anterior, middle, and posterior parts by the pericardium.

Pericardium

• The pericardium is a fibroserous membrane that covers the heart and the beginning of its great vessels.
• It is a closed sac composed of two layers: the fibrous pericardium and the serous pericardium.
• The fibrous pericardium is the tough, external layer, continuous with the central tendon of the diaphragm.

The Heart

• The heart is a muscular organ that pumps blood throughout the body.
• It has four chambers: the right atrium, left atrium, right ventricle, and left ventricle.
• The atria receive blood, while the ventricles pump blood out of the heart.

Surfaces of the Heart

• The anterior (sternocostal) surface of the heart is formed mainly by the right ventricle.
• The diaphragmatic (inferior) surface of the heart is formed mainly by the left ventricle and partly by the right ventricle.
• The right pulmonary surface of the heart is formed mainly by the right atrium.
• The left pulmonary surface of the heart is formed mainly by the left ventricle and forms the cardiac impression in the left lung.

Borders of the Heart

• The right border of the heart is formed by the right atrium and extends between the superior vena cava and the inferior vena cava.
• The inferior border of the heart is formed mainly by the right ventricle and slightly by the left ventricle.
• The left border of the heart is formed mainly by the left ventricle and slightly by the left auricle.
• The superior border of the heart is formed by the right and left atria and auricles.

Right Atrium

• The right atrium forms the right border of the heart and receives venous blood from the superior vena cava, inferior vena cava, and coronary sinus.
• The ear-like right auricle is a conical muscular pouch that projects from the chamber and increases the capacity of the atrium.

Interior of the Right Atrium

• The interior of the right atrium has a rough, trabeculated wall.
• The right atrium receives blood from the superior vena cava and inferior vena cava through the right atrioventricular orifice.

Right Ventricle

• The right ventricle forms the largest part of the anterior surface of the heart and small parts of the diaphragmatic and inferior surfaces.
• The right ventricle receives blood from the right atrium through the right atrioventricular orifice and pumps it into the pulmonary trunk.

Interior of the Right Ventricle

• The interior of the right ventricle has irregular muscular elevations (trabeculae carneae).
• A thick muscular ridge, the supraventricular crest, separates the ridged muscular wall of the inflow part of the chamber from the smooth wall of the outflow part.

Cardiac Conduction System

• The cardiac conduction system consists of nodal tissue that initiates and coordinates contractions of the four chambers.
• It generates and transmits impulses that produce the cardiac cycle.
• The cardiac conduction system includes the sinoatrial (SA) node, atrioventricular (AV) node, atrioventricular bundle (bundle of His), and right and left bundle branches.

Thoracic Aorta

• The thoracic aorta is the part of the aorta that lies in the thoracic cavity.
• It begins posterior to the 2nd right sternocostal joint at the level of the sternal angle and arches superiorly, posteriorly, and to the left.
• The thoracic aorta gives rise to several branches, including the brachiocephalic, left common carotid, and left subclavian arteries.

Branches of the Aorta

• The ascending aorta gives rise to the right and left coronary arteries.
• The arch of the aorta gives rise to the brachiocephalic, left common carotid, and left subclavian arteries.
• The thoracic aorta gives rise to posterior intercostal arteries, subcostal arteries, and some phrenic arteries.

Nerves of the Thorax

• The vagus nerve (CN X) enters the superior mediastinum posterior to the sternoclavicular joint and brachiocephalic vein and gives rise to the recurrent laryngeal nerve.
• The phrenic nerve arises from the anterior rami of C3-C5 nerves and passes through the superior thoracic aperture and runs between the mediastinal pleura and pericardium.
• The intercostal nerves (1-11) arise from the anterior rami of T1-T11 nerves and run in the intercostal spaces between the internal and innermost layers of intercostal muscles.

Muscle Damage and Hypertrophy

• External oblique muscle is most likely to be damaged.
• Anabolic steroid user may experience hypertrophy of the semispinalis capitis muscle.

Compression and Sensation

• Compression by the semispinalis capitis muscle can lead to reduced sensation in the scalp just posterior to the external ear.

Neck Flexion and Injury

• Difficulty in lateral flexion of the neck can be caused by hyperextension injury of the neck.
• Hyperextension injury of the neck can lead to acute back pain.

Case Study 2-11

• Sudden severe pain in the lower back can be caused by carrying a heavy load.
• Severe pain in the lower back can lead to a dull ache in the posterolateral aspect of the thigh, extending along the calf of the leg into the foot.
• Diagnosis of paraplegia and other neurological deficits can result in sphincter paralysis in the urinary bladder and anal canal.