PROCEDURE

d) Clavicle: Identify the clavicle, which extends from the superolateral aspect of the sternum (sternal end of the clavicle) lateral out to the shoulder.

2. Reflect the pectoralis major muscle superiorly and laterally (i.e. lifting it out of the way).
    (Figure206a) (Netter195) (Photo2080)

3. Force your fingers deep to the pectoralis minor muscle along its border to mobilize the muscle.
    (Photo2081)

4. Lift the pectoralis minor muscle and sever the attachments this muscle makes to the ribs (typically attached at the third, forth, and fifth ribs), such that you can reflect the muscle superolaterally.
    (Figure206, cut line) (Photo2082) (Photo2083)

Take care not to dissect or damage regions in the shoulder or armpit, those regions are part of the upper limb and should be preserved as intact as possible at this stage.

5. Lightly clean the sternum of connective tissue sufficiently to expose the thin ridge which is the manubriosternal joint.
    (Figure210) (Netter193) (Netter195) (Photo2025)

The manubriosternal joint is classified as a secondary cartilaginous joint.

Secondary cartilaginous joints are also known as a symphysis (the pubic symphysis is another example of this type of joint). Developmentally, this join arose from two bones and fibrocartilage grow across the gap (thus, the term 'secondary').

It is common in the elderly for the manubriosternal joint to partially or completely ossify (fuse with bone) such that there is no distinct joint and only a small ridge of bone.

The manubriosternal joint is commonly called the 'sternal angle' and is a landmark reference point. In the thorax at this horizontal level the trachea bifurcates into left and right mainstem bronchi and the aorta starts and ends the curve it makes as the aortic arch.

Radiology - On chest X-ray (a CTX, aka chest plate) note that the position of the sternum, sternal notch, and manubriosternal joint is obscured by the density of the more posterior vertebral column. (Rad2001a)

However, on a lateral film the distinct change in angle between the manubrium and sternum is more readily apparent. The joint space itself is fibrocartilaginous, so a faint hypodense line may be present in younger individuals or none at all if the space has fully ossified in the elderly. (Rad2002)

6. Clean connective tissue immediately lateral to the manubriosternal joint and identify the sternocostal junction of the second rib.
    (Figure210) (Netter192) (Netter193)

The first intercostal space is just superior to the second rib (i.e. between the first and second ribs).

The second intercostal space is just inferior to the second rib (i.e. between the second and third ribs).

Ribs 1-7 (true ribs) end anteriorly in costal cartilages that articulate directly with the sternum.

Ribs 8-10 (false ribs) attach in series to end in the costal cartilage of rib 7. That is to say 10 attaches to the cartilage of rib 9, then 9 attaches to 8, 8 attaches to 7, and finally 7 attaches to the body of the sternum.

Ribs 11 and 12 (floating ribs) articulate only with thoracic vertebrae. We will not see these until we study the posterior wall.

7. Clean connective tissue working superiorly from the manubriosternal joint up to the clavicle to observe the join of the first rib and the sternoclavicular joint.
    (Figure210) (Netter193)

Do not cut any tissue superior to the clavicle at this time. There are several important neck muscles attached to the clavicle that we need to preserve for study in the head & neck section of the course.

The sternoclavicular joint is a synovial joint attaching the upper limb to the body. This is the only bony joint attaching the entire upper limb to the body. This arrangement allows a wide range of upper limb motions to be performed.

Synovial joints have smooth articular surfaces of hyaline cartilage lubricated with a small amount of fluid, all surrounded by a capsule holding that lubricating fluid in place.

The sternocostal joint of rib 1 is classified as a primary cartilaginous joint. The costal cartilage of rib 1 is fused to the manubrium. All the other sternocostal joints are synovial type.

Primary cartilaginous joints arise developmentally from a single template of cartilage that forms bone from each end of the template. There was never a separation between the bones (thus, the term 'primary').

8. Palpate the ribs with your fingers and attempt to count the sequence of ribs.
    (Figure209) (Netter195)

Note, since rib 1 is located deep to the clavicle it cannot be palpated easily. Thus, we use rib 2 as the starting point for rib counting.

The floating ribs 11-12 are located posteriorly, so counting on the anterior thorax can occur accurately only from ribs 2-10.

Radiology - Ribs start higher on the posterior wall and angle anteriorly and inferiorly around to the front to connect to the sternum via their costal cartilages. The posterior more horizontal bony portion of the rib is more distinct on radiology than the anterior, mostly cartilaginous portion, that is hard to use to count (Rad2003). The anteroinferior trajectory of ribs is most readily apparant in a lateral film. (Rad2002)

9. Separate fascia along the lateral aspect of the chest to look for muscle fibers of the serratus anterior muscle.
    (Figure207) (Netter195) (Photo2084)

The serratus anterior muscle attaches from the first to eight or ninth ribs at a point between the mid-axillary and mid-clavicular line.

It is often not well defined in all individuals and can appear as muscle fingers interspersed with connective tissue. You may need to separate some of the lateral subcutaneous tissue to expose muscle fibers. 

Since the fibers attach only to the ribs, and not the spaces between the ribs, the muscle has a 'serrated' or 'saw tooth-like' pattern along the lateral chest wall. This pattern gives the muscle it's name.

The other end of the muscle (not visible) attaches to the scapula in order to pull the scapula flat on the back. Damage to the long thoracic nerve controlling the muscle during axilla or breast surgery would result in 'winged scapula' as the muscle can no longer pull the scapula flat to the back.

10. Clean the surface of the serratus anterior muscle till approximate the mid-axillary line to observe the direction of the muscle fibers.
    (Figure207) (Netter195) (Photo2084)

11. Force your fingers deep to the serratus anterior muscle along its inferior border at approximately the eight rib to mobilize the muscle.
    (Photo2085)

You will likely need to make a 'starter' hole with a small scalpel incision before your fingers can slide under the muscle itself.

12. Detach the anterior attachments of the serratus anterior muscle from the anterior rib attachment points and reflect the muscle laterally.
    (Figure208, cut lines) (Figure209)
    (Photo2086) (Photo2087)

In some individuals the serratus anterior muscle can be very small. If the muscle is small and attaching lateral (e.g. mid-axillary) it can be left in place as it will not interfere with the next lab.

At this stage the chest plate should be clear of major muscle attachments and ready to study in the next session.

CLINICAL EXERCISE - Resuscitative Thoracotomy

13. Interventions through the thoracic wall (thoracotomy) to gain access to the thoracic organs are performed for cardiopulmonary surgery or to gain rapid access to the organs during emergency resuscitative procedures.  

In this clinical exercise, you will perform a resuscitative thoracotomy on your donor in a mock emergency surgical intervention.

For the steps to take:
                              ------ click here ------

14. After performing the thoracotomy remove the Finochietto rib spreader.

15. Using a scalpel make an incision through the 1st intercostal space directly adjacent to the manubrium.
    (Figure210a)

The incision should be sufficiently long that you will be able to place the Lebsche knife in the opening in the next step.

16. Using the Lebsche knife cut through manubrium at the first intercostal space just inferior to the jugular notch.
    (Figure210b) (Photo2035) (Video2001)

Ensure everyone has the opportunity to use the Lebsche knife.  Those who did not use the blade on the inferior sternum separation should use it on this superior cut.

Swap roles approximately partway through the manubrium, so everyone gets a chance to use the Lebsche knife.

17. Using a scalpel, or scissors, cut through the soft tissue of the 1st intercostal space laterally from the manubrium extending out to a position slightly anterior to the mid-axillary line on both left and right sides.
    (Figure210c)

18. Using a Stryker saw, cut through the ribs along a line linking the lateral ends of the 1st and 5th intercostal cuts.
    (Figure210d) (Photo2088) (Photo2088a)

CAUTION. Wear eye protection when using saws, chisels, or bone forceps. Also, be wary of the sharp edges of cut bones. Cut ribs are particularly sharp.

Batteries for the Stryker saws are beside your computer/lights at your station.

These cuts have now separated the major attachments of the chest Plate

19. Elevate the inferior edge of the chest plate and insert a blunt probe, or your fingers, underneath to free the chest plate.

It is common in the elderly to have adhesions between the chest plate and membranes of the thoracic contents. If you encounter such adhesions, use your fingers to force/tear them as close to the chest plate as you can so as to leave most of the structures with the thoracic contents.

20. Examine the posterior side of the chest plate to find the internal thoracic artery and vein.
    (Netter196) (Netter197) (Photo2089) 

This artery typically runs along the inside surface of the chest plate immediately lateral to the sternum.

Similarly, there will be an internal thoracic vein running in proximity to the artery. Veins of a similar diameter have a thinner wall than their counterpart artery. Observe the internal thoracic artery is more rounded and thicker walled than the internal thoracic vein.

It is very common for the internal thoracic vein to bifurcate and run as a 'doublet' with a vein coursing on each side of the artery.

In older literature, and sometimes in the clinic, this artery/vein is called the internal mammary.

21. Dissect into the lateral edge of the sternum to remove fascia and expose the internal thoracic artery and small branches that arise from the artery. 
    (Netter196) (Netter197) (Photo2090) 

The internal thoracic artery (and vein) gives off lateral branches, the anterior intercostal arteries/veins, that enter into the intercostal spaces. With careful dissection you may see some of these delicate anterior intercostal vessel branches.

Veins often collapse flat in donors as a consequence of these thin walls and commonly contain residual amounts of clotted blood that does not get flushed clear during embalming.

The anterior intercostal vessels anastomose with the posterior intercostal vessels (deriving from the aorta). We will examine these in the posterior mediastinum lab.

22. On the inner surface of the chest plate just lateral to the lower third of the sternum, identify and clean the thin transversus thoracis muscle.
    (Netter196) (Photo2089) 

Transversus thoracis muscle is a thin plane of muscular and tendinous fibers situated upon the inner surface of the front wall of the chest. This muscle is part of the innermost intercostal muscle group.

The fibers of transversus thoracis angle from inferior attachments on the sternum to more superior attachments to the inner surfaces of the ribs.

The innermost intercostal muscles lie deep to the intercostal neurovascular bundle you examined above and have the same fiber orientation as those of the internal intercostal muscles (the only difference is these muscles lie deep to the neurovascular plane).

This innermost muscle is actually a group of three muscles with membrane spanning between each of the muscles in the group. These are the transversus thoracis (anterior), innermost intercostal muscle (laterally), and subcostalis muscle (posterior). Together, these three muscles make up the innermost intercostal muscle group.

The most prominent is the transversus thoracis muscle, with the other innermost intercostal group muscles small/indistinct on most elderly individuals.

23. At the cut surface of the ribs examine their cross sectional shape...you may find the magnifier in the special tools box useful to view the surface with magnification.
    (Netter193) (Photo2091) 

Ribs are a flattened bone tube, with an outer compact bone layer surrounding a small marrow chamber. The marrow chamber of the rib may have dark black/red material, this is red marrow.  Red marrow is capable of forming hematopoietic cells (not all marrow makes blood cells in adults, fatty marrow is termed 'white marrow' lacking hematopoietic capability).

Examine the inferior margin of the rib to observe a groove that runs the entire lower margin of each rib. This costal groove contains the intercostal neurovascular bundle. This is more readily apparent on a skeleton or in your atlas.

This bundle consists of an intercostal vein (positioned superior in the bundle), intercostal artery (positioned in the middle of the bundle), and intercostal nerve (positioned inferior)...the mnemonic V.A.N. for vein, artery, nerve is often used to remember their relative position in the bundle.

These diminish in diameter as they course from the posterior around to the anterior wall and can be somewhat small on the chest plate. We will examine this bundle again when dissecting the posterior thoracic wall.

24. Examine one of the intercostal spaces on the lateral aspect of the chest plate to observe fibers of the external intercostal muscle.
    (Netter197) (Netter261) (Photo2092) 

External intercostal muscles are the most superficial muscle layer spanning the ribs. The fibers of this muscle span between each pair of ribs and have an inferior, anterior and medial orientation.

The classic analogy is that of sticking one's hands in pants pockets with external intercostal muscle fibers oriented in the direction of the fingers in the pockets.

Move from the lateral aspect of the chest plate towards the sternum and observe that the external intercostal muscle becomes a translucent membrane as it approaches the sternum.

The membrane is sufficiently thin that you can see the internal intercostal muscle fibers through the membrane. Thus, to appreciate the presence of the membrane you may need to use a sharp probe to slide under the membrane and lift it.

25. Using a sharp probe separate fibers of the external intercostal muscle on the lateral side of the chest plate to observe the internal intercostal muscle fibers.
    (Netter197) (Netter261) (Photo2092)

The internal intercostal muscles are the middle layer with muscle fibers oriented obliquely at ~90 degrees to the orientation of the external intercostal muscles. 

The classic analogy is that of a 'cross-your-heart' with the internal intercostal muscle fibers oriented in the direction of the forearms.

The internal intercostal muscle becomes membranous along the posterior wall, whereas the external intercostal muscle became membranous on the anterior aspect.

26. When finished examining the chest plate retain it for future study/reference.

At the end of the session, we will place it back into position to protect the thoracic cavity contents.

27. Use your fingers explore the thoracic cavity contents.
    (Figure213) (Netter204) (Photo2026)

Examine how the lungs and heart are situated with respect to the chest plate and the connective tissue coverings over these organs. Pleura covers the lungs and pericardium covers the heart.

Note, the medial border of the left lung/pleura usually diverges to leave a part of the pericardium uncovered (the bare area of the heart) at the 4th and sometimes 3rd intercostal space.

This 'bare area' can vary in size depending on the heart and lung of the individual. This region permits needle access to the heart with low risk of puncturing the lung. 

Radiology - Compare the visual position of the lungs and heart to the representation seen in in CTX. Note the position of the heart makes a wider lateral excursion to the left compared to the right (about a 2:1 ratio for the amount of heart excursion on the left and right respectively). (Rad2004)

28. Typically, the parietal pleura remains attached to the chest plate and will have torn away from over the anterior lungs, however if there is any remaining anterior costal parietal pleura remove it from over the lungs.
    (Figure214) (Figure215) (Netter204)

Parietal pleura is subdivided for descriptive purposes into regions based upon the structures opposing the pleural region.

These are costal parietal pleura (anterior, lateral, and posterior following the ribcage), diaphragmatic parietal pleura (the region positioned against the diaphragm), mediastinal parietal pleura (medial pleura pressed against the mediastinum), and cervical parietal pleura (the cupola, or dome, region protruding into the base of the neck).

29. Using fingers explore the right and left pleural cavities surrounding the lungs with your hand.
    (Netter204) (Photo2027)

The space should be smooth and easy for your fingers to slide between the lungs and the body wall, diaphragm or mediastinum. However, in the elderly spot adhesions between the parietal and visceral layers of pleura are commonly present. If you encounter any, separate the two surfaces by forcing your fingers through the adhesion point. 

Note that you can slide your fingers within the plural cavity superior to the level of the clavicles (around the top, the apex, of the lung). The apex of the lung extends into the root of the neck superior to the clavicles several inches. This is readily apparent in a CTX where the apex of the lung is seen in relation to the clavicles. (Rad2004)

In the living, the parietal and visceral pleura layers are directly pressed against each other with only a thin sheen of fluid to lubricate movement. Thus, the 'space' of the pleural cavity is extremely small (just the fluid gap between two opposed membranes).

In patients with lung collapse, air or fluid pathologically accumulates creating a large gap that may need aspiration (via needle or tube) to remove the pathological material. 

During inspiration lung tissue moves down into the costodiaphragmatic recess. During expiration lung tissue moves out of the recess and only a thin sheen of fluid is present there between the pleura.

There is also a costomediastinal recess, although this is not as important as the costodiaphragmatic recess, since pathological fluid will accumulate in the lower costodiaphragmatic recess.

30. Using your hand retract the lung laterally away from the mediastinum to expose the anterior side of the root of the lung.

The root of the lung (also known as the hilum) is the location where structures enter and leave the lung. These are not visible and will be dissected in a later lab, at the moment you just see the smooth region of pleura over the lung root.

Major structures entering the lung are the bronchi and pulmonary arteries (carrying deoxygenated blood to the lungs), while leaving the lung are the pulmonary veins (carrying oxygenated blood back to the heart).

Additionally entering the lung are small bronchiole arteries supplying blood to the tissues of the lung and various autonomic nerve branches. Also leaving the lung are small branches of the lymphatic system.

31. Return the battery from the Stryker saw to the chargers at your station to ensure it is fully charged for the next use.

The batteries need to be pushed in firmly to the charger (thrust in even), the charge light should start blinking.

If an error light blinks try reinserting, if it continues to blink let the course director know so the battery can be discarded as faulty.

Post-Lab Daily Clinical Review Cases

Each lab has several multiple choice practice cases to reinforce understanding of the material within the lab and associated lectures. These are optional to review at home for consolidating and testing understanding.

Case 01

Case 02

Case 03

CHECKLIST

Skeletal Structures

Sternum
    Manubriosternal joint
    Sternocostal joints

Ribs
    Costal cartilage
    Costal groove
    Marrow chamber
    Intercostal spaces

Clavicle
    Sternoclavicular joint

Soft Structures

Pectoralis minor muscle

Serratus anterior muscle

External intercostal muscle
    External intercostal membrane

Internal intercostal muscle

Transversus thoracis muscle

Internal thoracic artery & vein
    Anterior intercostal artery
    Anterior intercostal vein

Lung (left and right)

Parietal pleura

- costal, cervical, diaphragmatic, mediastinal

Visceral pleura

Pericardium