THORACIC WALL
I. GENERALITIES - THORACIC CAVITY
A. Shape
1. Superior thoracic aperture (thoracic inlet) small and kidney-shaped (clinicians refer to it as thoracic outlet)
2. Infant, young child - more barrel-shaped
B. Contents:
1. Heart
2. Lungs
3. Great vessels relating to heart and lungs
4. Esophagus
5. Trachea
6. Vagus nerve
7. Phrenic nerve
8. Thoracic duct, etc.
C. Functions of the thorax
1. Provides protection for its contents
2. Provides attachment for many muscles besides those of thorax
3. Red marrow of ribs and sternum are principle sites of red blood formation
4. Able to allow expansion and contraction for respiratory function
II. BONY THORAX
A. Components
1. 12 thoracic vertebrae
2. 12 pairs of ribs
3. Sternum
B. Superior aperture of thorax
1. Bounded by
a. 1st thoracic vertebrae
b. first pair of ribs and costal cartilages
c. manubrium of sternum
2. Aperture allows passage of large vessels, nerves, trachea, and esophagus
3. On an oblique plane so that anterior boundary is 2 vertebral levels lower than the posterior boundary
C. Inferior thoracic aperture (outlet)
1. Bounded by
a. T12 vertebrae
b. the six lower pairs of ribs (the cartilages of ribs 7-12)
c. xiphoid process anteriorly
2. Closed by diaphragm which attaches to the lower 6 ribs and to the vertebral bodies
3. Costal arch = sloping costal cartilages of ribs 7-10
4. Infrasternal angle = angle the costal arch makes as the ribs converge on the lower sternum
5. Inferior aperture is not in a flat plane
a. posteriorly at level of T12
b. anteriorly at level of T9 (xiphisternal junction)
c. laterally at level of L1-2 (subcostal plane)
d. diaphragm pushes up into the thorax as high as T8 (ICS 5 on left, ICS 4 on right)
D. Thoracic vertebrae
1. Bodies are heart-shaped
2. Articular processes(3) are shaped to allow rotation-demifacets on body, costal facets on TP
3. Transverse processes are modified for articulation with the tubercles of the ribs
4. Articular facets for the heads of ribs are on the vertebral bodies
5. Vertebrae T2 through T8 have articular facets for two levels of ribs
6. Vertebrae T9-12 have only one articular facet for ribs on either side
7. Long spinous processes
8. Superior Demifacet – articulates with the head of its own rib
9. Inferior Demifacet - articulates with the head of the next lower rib
E. Ribs
1. 12 pairs, curve anteriorly and inferiorly from thoracic vertebrae
2. Subdivided according to their anterior articulation
a. True ribs: (R1-7) articulate with sternum
b. False ribs: (R8-12) R8-10 articulate with next highest rib
c. Floating ribs: (R11-12) no anterior articulation
3. Typical rib (R3-9)
a. Head - articulates with vertebrae of same number plus next highest vertebrae (i.e. has 2 articular facets - R5 with T4 and T5)
b. Neck: tapered area just lateral to the head, medial to tubercle - superior part called the crest
c. Body: (shaft) most of rib, from neck to its anterior articulation. Has a twist in addition to other landmarks
i. Tubercle - articulates with transverse process of vertebrae of the same number
ii. Angle - where shaft turns sharply anteriorly, just lateral to tubercle
iii. Costal groove - inside of lower border – contains v., n., a.
4. Atypical ribs - R1,2,10,11,12
a. Rib 1: no twist to its body, single facet on head, scalene tubercle, grooves for subclavian vessels, broadest and most curved, flat and short
b. Rib 2: tuberosities for scalene mm. and serratus anterior mm.
c. Rib 10: articulates only with vertebrae 10
d. Ribs 11,12: small costal cartilage, single facet on the head, no neck or tubercle-thin cartilage, no costal groove
5. Costal cartilages - hyaline cartilage
a. 1st cartilage fuses with R1 and manubrium-sternochondral joints
b. cartilages 2-10 involved in synovial joints at one end (with sternum or higher rib), fused with rib at other end
c. cartilages 11-12 are pointed and end in muscles of anterior abdominal wall
F. Sternum - 3 parts
1. Manubrium
a. Superior portion of sternum
b. Articulates with clavicles, R1, R2 and sternal body
c. Suprasternal notch (jugular notch) on superior border
d. Anterior to T3 & T4 vertebrae
e. Attachment for SCM & pec. major, sternohyoid, and sternothyroid
2. Body of sternum
a. 4 original sternabrae, fused in adult
b. Articulates with R2-7, manubrium and xiphoid process
c. Forms the sternal angle (of Louis) where it articulates with the manubrium @T4
d. Anterior to T5-9 Vertebrae
3. Xiphoid process
a. Articulates with lower edge of sternal body and R7
b. Cartilaginous at birth, then ossifies
c. Important landmark
i. inferior limit of thoracic cavity anteriorly
ii. midline point for diaphragmatic surface of liver, diaphragm and inferior border of heart
d. Linea alba attaches to this portion of the sternum
III. ARTICULATIONS OF THE BONY THORAX
A. Costovertebral joints
1. Costovertebral proper - between costal heads and vertebral bodies and discs
a. gliding synovial joint
b. associated radiate and intra-articular ligaments
2. Costotransverse - between tubercles and transverse processes
a. gliding synovial joint
b. associated costotransverse ligament
B. Costochondral - no movement, no joint space - fused by periosteum
C. Sternocostal
1. R1 - synchondrosis-cartilaginous joint
2. R2-7 - gliding synovial joint with radiate ligaments
D. Interchondral - simple gliding synovial joint-between cartilages 6-7,7-8,8-9
E. Intersternal - symphysis that convert to synostoses with aging (includes manubriosternal and xiphisternal joints)
F. Intervertebral
IV. MUSCLES OF THE THORACIC WALL PROPER
A. Intercostal muscles - hypomeric origin
1. External intercostals
a. Located between ribs, arise from an upper rib and pass antero-inferiorly to next lower rib
b. Eleven pairs
c. Extend from the tubercles of the ribs to the costochondral junctions
d. Their plane is continued anteriorly to the sternum by the external intercostal membrane
e. Continuous inferiorly with external oblique muscles of abdominal wall
2. Internal intercostals
a. Arise from an upper rib, pass inferior-posteriorly to the rib below
b. Eleven pairs
c. Extend from the angle of the rib to the sternal edge
d. Their plane is extended posteriorly by the internal intercostal membrane
e. Continuous inferiorly with internal oblique muscles of abdominal wall
3. Innermost intercostals
a. Same fiber course as internal intercostals but deeper
b. Nerves and vessels are located between the internal and innermost intercostals
c. Cover approximately the middle half of an intercostal space - extend anterior as transversus thoracis
d. Thickness and extent vary
e. Sometime considered as deep lamina of internal intercostals
4. Subcostals
a. In same plane and fiber direction as innermost intercostals
b. Located near angles of the ribs - in reality a specialized portion of innermost intercostals
c. Recognized because they cross two or three intercostal spaces
B. Transversus thoracis (sternocostal) muscle
1. Arise from xiphoid process, inferior body of sternum, costal cartilages
2. Pass superolaterally to costal cartilages 2-6
3. Same plane as innermost intercostals
4. Vessels and nerves run between sternocostals and internal intercostals
5. Continuous inferiorly with transversus abdominus muscle
C. Nerve and blood supply - intercostal nn. and aa. (Remember: “VAN” (See below))
D. Actions
1. Elevate the ribs - inspiratory muscles
2. Keep intercostal spaces rigid
E. Diaphragm - discussed later
F. Endothoracic fascia = plane of connective tissue on deep surface of intercostal muscles - extends into the neck and attached to diaphragm inferiorly
V. INTERCOSTAL NERVES
A. Ventral rami of T1-11 of "typical" spinal nerve
1. Lateral cutaneous branches with anterior and posterior branches
2. Anterior cutaneous branches with medial and lateral branches
B. Located inferior to intercostal artery just inferior to rib margin (costal groove) and between internal and innermost intercostals –
{REMEMBER: “VAN” – from the inferior edge of the rib’s costal groove, the intercostal Vein is most superior, followed by the Artery and then the Nerve}
C. Named by space they are in (# of higher rib)
D. Collateral branches are located just superior to the next lower rib
E. Eleven true intercostal nerves
1. T1-6 = thoracic intercostal nerves
a. T1 is small since its ventral ramus contributes to the brachial plexus
2. T7-11 = thoracoabdominal nerves because they continue anteriorly to abdominal wall
F. Subcostal nerve = T12, below R12
G. Functions
1. Cutaneous distribution to dermatomes
2. Innervation of myotomes
H. Branches
1. GRC and WRC
2. Collateral branches
3. Lateral cutaneous branch
4. Anterior cutaneous branch
5. Muscular branch
VI. POSTERIOR INTERCOSTAL ARTERIES
A. Most arise from the thoracic aorta, pass to intercostal space and run in same plane as the nerves - just superior to nerve
B. Upper two intercostal aa. (superior intercostal arteries) are secondary branches of the subclavian artery (costocervical trunk)
C. Follow the course of the nerve with same general branches
D. End by anastomosing with anterior intercostal branches of the internal thoracic artery - 2 per space
E. Branching pattern similar to nerves
VII. INTERNAL THORACIC ARTERY
A. Arises from the subclavian artery in the root of the neck
B. Located just lateral of sternum, lies on the pleura
C. Located between sternocostalis and internal intercostal mm.
D. Ends at the 6th intercostal space by dividing into its terminal branches
1. Musculophrenic
2. Superior epigastric
E. Branches
1. Cutaneous branches - perforate muscle and supply anterior midline
2. Anterior intercostals - run laterally in intercostal spaces - anastomose with posterior intercostal - upper 5-6 ICS, 2/space
3. Pericardiacophrenic - runs along phrenic nerve to diaphragm - to pleura also
4. Mediastinal branches - to anterior mediastinum
5. Musculophrenic - runs along costal cartilage - provides lower anterior intercostals (T7-T9)
6. Superior epigastric - runs posterior to 7th costal cartilage, continues inferiorly in the rectus sheath to anastomose with the inferior epigastric artery
F. Internal thoracic vein - accompanies artery - paired venae comitantes – drain to subclavian
VIII. INTERCOSTAL VEINS
A. Similar course to intercostal arteries
1. Posterior veins drain to azygous system
2. Anterior intercostals drain to internal thoracic vein
3. Contain Valves
IX. LYMPHATICS
A. Groups of nodes
1. Parasternal nodes
a. located along internal thoracic vessels
b. receive drainage from
i. medial chest wall (including medial breast)
ii. upper abdominal wall
iii. upper surface of liver
c. efferents to bronchomediastinal trunk
2. Intercostal nodes
a. located near heads of ribs, along intercostal vessels
b. drain intercostal space and posteriolateral chest wall
c. efferents to thoracic duct
3. Phrenic nodes
a. located along upper diaphragm
b. anterior, middle, posterior sets
c. afferents from liver, abdominal wall, diaphragm
d. efferents to parasternal nodes and posterior mediastinal nodes