DANTE JOSE D. MERCADO, MDCHIEF OF SECTION GROSS ANATOMYTHORACIC WALL

OBJECTIVESAnalyze the articular surfaces on these bones with regards their possible movements: - ribs, sternum and thoracic vertebrae. Determine the boundaries of the thoracic inlet and discuss its functional and clinical significance.Identify the following landmarks on the chest of a live subject: sternoclavicular junctions; jugular notch; sternal angle of Louis; ribs composing the costal arch; level of the nipple; anterior and posterior axillary folds; and at the back, the vertebra prominens, crest of the scapular spine, vertebral border and inferior angle of the scapula.Indicate these reference lines on an illustration of the chest or on a live subject: midsternal, midclavicular; anterior, posterior, mid-axillary and scapular lines.Discuss the significance of the origin, course and position of the intercostal neurovascular structures.Differentiate these deformities: pectus excavatus; pigeon breast; barrel chest; scoliosis and kyphosis.

Soft Tissue Landmarks

Muscular and membranous components inherent to the thoracic wall:

External and Internal Intercostal Muscles and membranes: - attached to the superior and inferior borders of each rib; and occupying each intercostal space (ICS)fibers of these 2 muscles cross each other obliquely in each ICS. (To verify, cut the attachments of a few external intercostal muscles along the inferior border of the rib and carefully cut the fibers from those of the underlying internal intercostal muscle.)fibers of each external muscle fill each ICS from the vertebral border to the costo-chondral junction; those of the internal muscle range from the sternal border to the angles of the ribs dorsally. the unoccupied areas are filled with the corresponding anterior and posterior intercostal membranes.innervated by corresponding intercostal nervesThe traditional view: the external intercostals elevate each rib, while the internal intercostals depress the ribsothers recently support the view that both muscles elevate each rib, allegedly supported by electro-myographic studies. Whichever concept is considered, the muscles are respiratory muscles in the sense that they help to expand and contract the thoracic wall thus affecting the diameters of the thoracic cavity.

PedicleLamina

Superior articular processInferior articular processArticular process fro head of the rib

The common middle rib consists of the neck that is closest to the thoracic spine with an articular tubercle, the angle of which is a curved portion of the rib, and the distal body. The subcostal groove is best seen when viewed from the back. The costal artery and nerve follow the subcostal groove.

1st RibThe first rib is one of the upper, specialized ribs. Important features include the attachment of the scalenus medius muscle and the serratus anterior muscle. A groove for the subclavian artery and vein represent important potential areas of serious injury in fractures of the first rib.

10th RibDrawing of the 10th rib. Note that the 10th rib has a single articular facet. No direct anterior connection to the sternum is present. The forms of the 10th, 11th, and 12th ribs are similar.

Typical RibsTypical upper thoracic rib. Each of the upper 9 thoracic ribs has 2 posterior articulations with a thoracic vertebral body above and below (CVJ) and an anterior articulation with the sternum (CCJ).

INTERCOSTAL NERVE BLOCK

Intercostal nerve block is intended to anesthetize the intercostal nerves in anticipation of performing minor surgery on some part of the thoracic wall (e.g. removal of a skin tag, sewing a laceration,) and to relieve pain in a rib fracture.The posterior angle of the rib is palpated and the anesthetic introduced along the lower edge of the rib selected. The aim is to bathe the intercostal nerve with the local anesthetic and eliminate sensation in the intercostal space anterior to this point. Remember that several intercostal nerves must be blocked to achieve real anesthesia in just one segment because of the presence of collateral branches.

External Intercostal Muscle & Anterior Intercostal Membrane

Internal Intercostal Muscle& Posterior Intercostal Membrane

At the inner surface of the chest wall:

Sterno-costalis (or transversus thoracis or triangularis sterni) - has narrow origins from the deep surface of the xyphoid process and adjoining 6th and 7th costal cartilages. The fibers expand laterally and superiorly to the costal cartilages of the 2nd to the 4th ribs. The muscle pulls down to a certain extent the corresponding ribs to which the fibers are attached during forced expiration. It also maintains the position of the internal thoracic vessels alongside the lateral sternal border.Along the internal surface, among the lower ICS, many of the deeper fibers of the internal intercostal muscles are separated by the passage of the intercostal neurovascular structures. These separated fibers are often referred to as the innermost intercostal muscles. More posteriorly, some of these muscle slips bridge through one or more ribs to be attached to higher ribs, to be distinguished as subcostal muscles.

Movements of the Thoracic WallCosto-vertebral synovial joints allow upward, outward and limited backward movements of the ribs.The elastic cartilages allow forward expansion, thrusting the sternum forwards and upwards, thus increasing the antero-posterior (AP) diameter of the thoracic cavity.Ribs 7 to 10 are pulled upwards and backwards (bucket-handle-caliper movements, by Grant) which increase the diameters of the lower part of the thoracic cavity. Demonstrate.The last two pairs of ribs are held fixed by the attached abdominal muscles and the serratus posterior.Furthermore, the tone of the intercostal muscles maintain the tension of each ICS to counteract the inward pull of the contracting respiratory diaphragm and intra-thoracic pressure.For very deep, forced inspirations, the action of other extrinsic muscles attached to other parts of thoracic cage help in the expansion of the thoracic cavity. What are those muscles?

Respiratory Diaphragm

Expiration results from the elastic recoil of the lungs, ribs and costal cartilages upon relaxation of the above-named muscles. In forced expiration, the abdominal muscles are called into play, including other muscles in other regions for increased support and fixation purposes.

Accessory Muscles

Intercostal NervesIntercostal nerves - extensions of the anterior rami of the 12 pairs of thoracic spinal nerves.These nerves initially occupy the middle of each ICS with the accompanying blood vessels situated above each nerve, thus arranged as V.A.N.At the costal angles, these N.V.S. fit in the costal groove of the upper rib, held and protected by strips of fascia and occasional fasciculi of the innermost intercostal muscles. Each intercostal nerve is composed of 3 kinds of fibers:a. Motor fibers b. Sensory fibers from the cutaneous areas and some from the parietal pleura. c. Sympathetic fibers (GVE) for smooth muscles around blood vessels; and secretory fibers to the glands in the skin.

The lower 6 intercostal nerves extend their fibers to corresponding structures at the antero-lateral aspect of the abdominal wall.

The Intercostal ArteriesAnterior set - consists of a pair of slender arteries for each ICS, coursing along the upper and lower borders of each rib. Branches of the internal thoracic artery which courses downwards after arising from the parent trunk which is the subclavian artery.

Upon reaching the 6th ICS level, the internal thoracic divides into its 2 terminal branches: lateral musculo-phrenic artery coursing along the inner border of the costal margin giving intercostal branches for the 7th,8th and 9th ICSthe superior epigastric artery which continues descending vertically on the inner surface of the anterior abdominal wall to supply its tissues.

Posterior set - 9 single arteries for each ICS arising from the thoracic aorta starting with the 3rd ICS down to the 12th, which is called subcostal artery since it is below the 12th rib. The first two posterior intercostal arteries arise from the superior intercostal artery, which is a branch of the costo-cervical trunk of the subclavian. At the angle of the ribs, each artery divides into an upper and a lower branch to anastomose with the anterior arteries in each ICS.The 10th and 11th ICS are supplied by the posterior arteries only. The subcostal artery supplies the postero-lateral abdominal wall.

The intercostal veins are positioned above the arteries. Anterior set, from the 1st to the 3rd ICS drain into the internal thoracic vein. The veins in the lower 4th-9th ICS drain into the musculo-phrenic vein. This vein joins with the ascending superior epigastric vein to form the single internal thoracic vein at the level of the 3rd ICS.The posterior set:The lower 4th-11th intercostal veins at the right side drain into the azygos vein that ascends from the abdominal cavity alongside the lumbar vertebrae. The left veins drain into an inferior hemi-azygos vein (if present) also from the abdominal cavity. The first intercostal veins drain into the vertebral or brachio- cephalic vein.The 2nd and 3rd veins unite to form a superior intercostal vein which drains into the azygos at the right and into a superior hemiazygos at the left.

Intercostal NVS

Surgeons must be very carefulWhen they take the knife!Underneath their fine incisions stirs the culpritLIFE!

DJDMERCADO, MD