Thorax 1: Anatomy of the Thoracic Wall

Thoracic Skeleton consists of:

Sternum

12 pairs of ribs and the associated costal cartilages

12 thoracic vertebrae and their associated intervertebral (IV) discs

Intervertebral (IV) discs are joints located b/w the vertebrae

STERNUM: Flat elongated bone that forms the anterior and middle portion of the thoracic cage

Composed of three parts:
1. Manubrium
2. Body
3. Xiphoid Process

**Sternal angle (Angle of Louis) is the articulation b/w the manubrium & the body

**The sternal angle:

marks the 2nd rib w/associated costal cartilage is opposite of ~T4/T5 thoracic vertebrae (highlighted by yellow box)

STERNUM:

Jugular Notch:

easily palpable concave notch along superior border of the manubrium

COSTAL CARTILAGES

Prolong the ribs ANTERIORLY

Contribute to the elasticity of the thoracic wall

First 7 generally articulate DIRECTLY w/the sternum

The 8th, 9th and 10th articulate with the cartilages just SUPERIOR to them

Thoracic Apertures

The thoracic cage has superior and inferior openings (apertures)

Superior Thoracic Aperture:
doorway b/w thoracic cavity and the neck

Clinicians generally
refer to the superior thoracic
aperture as the “thoracic outlet”

Inferior Thoracic Aperture:
the muscular diaphragm closes the aperture, separating the thoracic cavity from the abdominal cavity

General Features of Thoracic Vertebrae:

Like most all vertebrae, a typical thoracic vertebra consists of three major features:

1. Vertebral body: for weight bearing

2. Vertebral (neural) ARCH consisting of pedicles and laminae:
protection of the spinal cord

3. Numerous (7) processes for:
muscular attachment and joint surfaces

VERTEBRAL BODIES ARE heart-shaped and have costal facets for articulation with ribs

SPINOUS PROCESSES are long and slant inferiorly

TRANSVERSE PROCESSES are long and slender and have a transverse costal facet for articulation with the tubercle of a rib

ARTICULAR FACETS (4) for articulation with adjacent vertebrae (i.e. facet joints)

Three types of RIBS:

1. Vertebrocostal (True):
articulates directly with sternum via its own costal cartilage (1-7)

2. Vertebrochondral (False):
indirect articulation with sternum via costal cartilage of the superior rib (8-10)

3. Vertebral (Floating):
do not articulate with sternum, end in the posterior abdominal wall (11-12)

Characteristics of typical Ribs:

Typical ribs are considered ribs 3-9

HEAD:
has two facets (superior and inferior) for articulation with two vertebrae.
**There is a crest b/w these two facets

Neck:
slightly constricted area just distal to head

Tubercle:
located at junction of neck and shaft, has a smooth facet for articulation with corresponding transverse process of the vertebra

Shaft:
thin, flat and curved.
Has a costal angle where rib turns anterolateral and a COSTAL GROOVE inferiorly for neurovascular structures

Typical Rib ARTICULATIONS:

Understand that the head of typical ribs articulates with TWO vertebrae:

1. The body of the numerically corresponding vertebra and also 2. the body of the vertebra superior to it

Example: Rib 5 articulates with the body of T5 and T4

Understand that the tubercle of a typical rib articulates with the numerically corresponding transverse process

JOINTS of the Thoracic Skeleton

The thoracic skeleton consists 3 major types of articulations (joints):

1. Costochondral

2. Sternocostal

3. Costovertebral

All VERY STRONG articulations aimed to protect underlying structures!

JOINTS of the Thoracic Skeleton Cont'd...

Costochondral = fibrous joints

Sternocostal = synovial joints

Costovertebral = synovial joints

MUSCLES of the Thoracic Wall

Several EXTRINSIC muscles of the upper limb cover the thoracic wall but are primarily muscles of the upper limb

These include:

Pectoralis Major
Pectoralis Minor
Serrratus Anterior

These muscles, although primarily move and stabilize the upper limb, they can also assist in respiration by moving the ribs and thoracic cage

PECTORALIS MAJOR

Large fan-shaped muscle in superior thorax

Two heads of origin: clavicular and sternocostal

Inserts into the humerus

Powerful ADDUCTOR; flexor, and medial (internal) rotator of the arm

***Innervated by the medial & lateral pectoral nerves

PECTORALIS MINOR

Originates from anterior surface of the 3rd - 5th ribs

Inserts into the coracoid process of the scapula

Stabilizes the scapula against thoracic wall (accessory respiratory muscle also)

Innervated primarily by the MEDIAL pectoral nerve (receives a small contribution by the lateral pectoral nerve)

SERRATUS ANTERIOR MUSCLE

Originates on the surface of the 1st - 8th ribs

Inserts into the medial border of the scapula

Stabilizes and protracts the SCAPULA (shoulder blade)

**Innervated by LONG thoracic nerve

INTRINSIC MUSCLES of the Thorax

External Intercostals
Internal Intercostals
Innermost Intercostals

Intercostal muscles are all accessory muscles of respiration

Innervated by intercostal nerves

Note the order “VAN” of neurovascular structures within the costal groove:
Intercostal Vein
Intercostal Artery
Intercostal Nerve

Small collateral branches… (minor significance, "angel hairs")

If we removed the anterior aspect of the thoracic wall….

Note the internal thoracic arteries divides into the MUSCULOPHRENIC and SUPERIOR EPIGASTRIC arteries

Nerves of the Thoracic Wall Cont'd...

This segmental innervation pattern is reflected on the surface of the body

Note in this dermatome map, the thoracic nerves innervate successive segments along the body wall

Every sensory nerve innervates a specific skin area

These “dermatomes” then correspond to a specific spinal cord segment

The dermatomes are arranged in a “band-like pattern

Note that the T4 dermatome corresponds to the level of the nipples

Note that the T10 dermatome corresponds to the level of the umbilicus

Lateral Chest X-Ray

BOTTOM LINE CONCEPTS

ACC
Anatomical Connection to the Clinic:

65 yo male, falls in bathroom, hits chest on bathtub, left side chest pain, pain worsens when breathing deeply

Severe point tenderness over the lateral aspect of his chest wall (w/superficial swelling & bruising)

Need chest x-ray

Diagnosis?
Possible complications?