PROCEDURE

Throughout this course, unless otherwise indicated in the dissection instructions, you are expected to dissect both the left and right side of the body.

As both good surgical practice, and out of respect for our donors, leave regions of the body covered when they are not part of the day's dissection.

Ensure that you liberally apply wetting agent to exposed surfaces whenever you observe the surface drying.

Introductory Pre-Work Guides (review before lab)

0. PRE-WORK (before lab) review the

Muscle Nomenclature - This page contains a list of general principles of muscle nomenclature and tor insertions/origins of muscles. 

Muscle Actions - A list of the conventions used to describe how muscles move joints and other structures.

Tendons and Ligaments - A summary primer on the terminology associated with tendons and ligaments, which can be confusing at times.

1. PRE-WORK (before lab) review the organization of the bony structures of the back from your atlas.
    (Figure101)

a) On the scapula, observe the vertebral border of the scapula (i.e. the medial edge). This border (edge) of the scapula runs from inferior to superior, parallel to the spine. The superior end of the vertebral border is called the superior angle. The inferior end of the vertebral border is the inferior angle. The spine of the scapula arises on the superior half of the posterior side of the scapula. This ridge of bone extends laterally to the shoulder, ending in the acromion at the tip of the shoulder. (Netter410)

b) On the pelvic bone observe the iliac crest. This arch of bone ends at the most posterior side in a bony bump, the posterior superior iliac spine. (Netter334)

c) Along the vertebral column, each vertebra has a posteriorly directed spinous process. Spinous processes serve as anchor points for ligaments and muscles of the back.
(Netter162) (Netter163)

d) The cervical vertebra C7 has the longest spinous process of the cervical vertebrae and is commonly called the vertebra prominens due to its length. (Netter162)

e) On the skull, observe the external occipital protuberance, a 'bump' at the most posterior midline aspect of the skull base. On the posterolateral aspect of the skull, just posterior to the earlobe, is the bony bulge of the mastoid process. (Netter013)

The external occipital protuberance is the most superior attachment point for the ligamentum nuchae (ligament of the neck). The ligamentum nuchae is a fibrous membrane which extends as an anterior to posterior sheet from the external occipital protuberance inferiorly along the spinous processes of all the cervical vertebra. (Netter029)

2. Locate the Patient Chart on the bookstand and remember through this course to note any key information about conditions you come across within your patient.
    (Example Chart)

The Patient Chart serves as a record of the history and physical of your patient.

If you determine they have had a past surgery, procedure, or anatomic variant add notes on what you have determined to that section on the Patient Chart.

The Patient Record serves as a detail of the patient for the MS1 and MS2 teams who, in turn, add additional details found in the patient with each course.

3. Turn the donor to the prone position (face down).

Before turning the donor over, remove the moist cloth completely so it doesn't get caught underneath the donor while turning them over.

When the donor has been turned prone, replace the cloth cover over lower extremities and buttocks. The face covering can be placed across the upper scalp.

When you turn a donor over, the hole in the plastic liners above the center drainage point in the table can get shifted. If you notice the drainage is blocked in later labs, make a 1-2cm slide through the plastic liners above the drainpipe to assist drainage.

4. Position one of the wood support blocks horizontally under the upper chest.
    (Figure101a)

The wood support blocks are on the foot of the shelf under your table. At the end of a lab blocks should be returned to this location.

This wood block will elevate the shoulders making access to the skin of the neck easier.

5. Attempt to palpate the following bony landmarks and use a skin marker pen to indicate their positions on both the left and right side of the donor.
    (Figure101) (Netter161) (Photo1046)

Send a member of your team to the supply table for several of the purple skin pens to use in the steps.

Dry excess moisture from the skin on the back with paper towel as markers do not apply well to overly wet surfaces. 

The disposable skin marker pen tips can become 'clogged' with moisture or skin cells. If the pen does not make a mark, wipe/clean the marker pen tip on a dry paper towel and wipe/dry the skin surface further with a fresh paper towel.

The marks do not need to be perfect, or even neat, they serve only as a surgical guide. So if a skin location doesn't mark well do not be concerned.

Understanding landmarks, and correctly identifying them, are key components of making correct incisions during surgery. Of particular use are the palpable landmarks, meaning those bony landmarks that can be readily felt during physical examination of the average patient.

Identification by palpation on the back can be somewhat difficult in donors due to higher tissue density following embalming and in larger individuals with extensive subcutaneous tissue.

Do not worry if you cannot feel all the landmarks, just make your best guess. It will be helpful later to try palpating these landmarks on yourself or a willing partner.

On the upper back: Palpate for the vertebral border of the scapula and the superior/inferior angles. Place a skin marking over these landmarks

On the posterior skull: Palpate for the external occipital protuberance (back of the skull) and for the mastoid process (lateral on the skull just inferior to the ear). Place a skin marking over both.

On the pelvic region: Palpate for the bony ridges of the posterior side of the sacrum and place a skin marking at the midline where you feel the sacrum.

On the pelvic region: Palpate laterally for the arch of the iliac crests. In individuals with thick subcutaneous tissue, you may not be able to locate these (make a 'best guess' mark on each side approximately two inches superior to the level of the sacrum).

6. Before cutting into the skin, incision lines are marked on a patient as part of surgical planning.
    (Figure101b) (Photo1047)

Our marking positions need only be approximate. It will not affect the dissection if you end up a little superior/inferior  or lateral/medial with the lines.  

Successful outcome of surgical procedure is, logically, strongly correlated with the surgeon getting the initial incisions in the correct place. 

Along the midline of the back: Mark a dashed line along the midline from the external occipital protuberance inferiorly to the sacrum. In the upper back typically you can feel the ridge of bony protrusions of the vertebral spinous processes (in lumbar/neck regions make an estimate of the midline).

On the back: Mark a horizontal dashed line just inferior to the level of the inferior angle of the scapula. This will be the mid-back incision line.

On the pelvis: Mark a horizontal dashed line just superior to the location of the sacrum landmark. This will be the sacral incision line.

On the back: Mark a horizontal dashed line mid-lumbar at approximately halfway between the other back lines. This will be the mid-lumbar incision line

On the shoulders: Mark a horizontal dashed line just superior to the level of the superior angle of the scapula (essentially just across the base of the neck/shoulders). This will be the shoulder incision line.

On the skull: Mark a horizontal dashed line between the external occipital protuberance and mastoid process markings. This will be the cranial incision line.

These incision markings demarcate a series of skin flaps that will be reflected laterally in the following steps. These skin flaps are lumbar flaps, lower back flaps, upper back flaps, and neck flaps. (Photo1048)

7. At the mid-back incision line make a shallow horizontal incision in the skin approximately 2 inches long on each side of the midline.
    (Figure102, cut #1)

With your 'first cut' into the skin it can be difficult to determine how deep to make the cut. In this region of the back the skin overlying the muscles is relatively thin.

Aim to have 3-5mm depth in this first incision. In steps below, where you retract the skin, the depth of the cut will become apparent and you can go deeper or shallower as needed to be in the plane between skin and the muscles of the back.

If you have not already reviewed the video on skin incisions, take a moment to review the video instruction section with this link.  ---- click here ---->

8. Make another shallow incision approximately 2" long extending superiorly from the middle of your horizontal cut forming an 'upside down T'.
    (Figure102, cut #2)

9. Using a hemostat (locking forceps), clamp the skin at the corner where the incision lines intersect and pull the corner of skin so that you can make small incisions under the lifted edge to begin reflecting the skin. 
    (Figure104)

10. Widen and deepen the cut until you reach the plane between the superficial fascia (hypodermis) and deep fascia covering the muscles of trapezius and latissimus dorsi.
    (Figure103)

At this point you can observe the depth of the cut and identify the layers of the integument (skin). From superficial to deep these layers are the epidermis, dermis, and hypodermis.

Epidermis: The epidermis is less than 1mm thick and will exhibit different degrees of pigmentation depending on the individual.

Dermis: The dermis is a stronger layer of connective tissue (dense irregular connective tissue) up to several millimeters thick that is fused tightly to the epidermis. To the eye, the dermis typically exhibits a relatively uniform pale color.

Hypodermis: The hypodermis varies widely in thickness depending on the region of the body. In this mid-back region it may range from a few millimeters up to a centimeter, however, when you get to the region of the lower back the thickness of the hypodermis can be several inches. The hypodermis in a well nourished individual will have extensive 'marbling' consisting of regions of fibrous connective tissue and regions of yellow appearing adipose connective tissue. Throughout the hypodermis are numerous small blood vessels and nerves (most of these will be too small to be seen).

The deep or investing fascia is not considered part of the integument. Deep fascia surrounds and encases muscles of the body (thus the alternate term 'investing' fascia). On the back, the deep fascia layer lies immediately below the hypodermis and directly on the surface of the superficial back muscles.

Deep fascia is a very thin layer that typically has a white smooth membranous appearance. Muscle tissue underneath the deep fascia is darker and has a distinct appearance consisting of parallel fascicles.

Each of these fascicles is formed by bundles of individual muscle cells. On the upper back where you are dissecting, these muscle fascicles will belong to the trapezius muscle (we will examine the trapezius muscle and other back muscles in detail later in the next lab).

If you find yourself cutting into muscle tissue you are dissecting too deeply and need to move more shallowly back to the correct plane.

11. Use your hemostats to apply continuous tension as you retract the skin and separate along the plane between the superficial fascia and the deep fascia.
    (Figure104)

It may help to have a member of the team keep tension on the skin while a second member is cutting.

Hold the scalpel at an angle and use long smooth slicing motions cutting with the tip of the blade. Each cut should aim to separate a few millimeters of tissue, allowing you to observe what you are cutting through while making the incisions.

Avoid sawing motions as they have less control and can result in jagged edge cuts that in the living may not heal as well as a smooth cut.

In some regions pushing your fingers into the plane between the superficial and deep fascia will separate the tissue readily.

As needed, extend the superior and horizontal skin incisions such that you can progressively reflect the skin flap.

If you have not already reviewed the video on removing skin and superficial fascia, take a moment to review the video instruction section with this link.  ---- click here ---->

12. Extend the midline incision superiorly until you reach the shoulder incision dashed line.
    (Figure105)

Observe that the superficial fascia becomes thicker and more fibrous in the superior region of the back.

13. Make lateral incisions following the shoulder incision mark lines horizontally to form a second 'T' incision.
    (Figure105)

14. Extend both the mid-back and shoulder horizontal incisions laterally while reflecting the upper back skin flap laterally to the level of the axilla. 
    (Figure105)

Axilla is the anatomic term for the armpit. A common reference term in this region is the 'midaxillary line'. This is an imaginary line that runs inferiorly from the armpit along the lateral side of the thorax.  It divides the body into anterior and posterior halves in the coronal plane.

At this stage in dissection you should have a superior left and superior right upper back skin flap reflected.

Leave these skin flaps and all subsequent skin flaps attached along their lateral edges so you can use the flaps to cover the area of back from where they were reflected.

15. At the midline on your shoulder horizontal incision, make a vertical incision extending several inches superiorly on the neck.
    (Figure105b)

16. Using hemostats grasp the exposed corner of skin on the neck and begin reflecting the skin of the neck superiorly and laterally following the plane between the hypodermis and deep fascia.
    (Figure105c)

The thickness of the fascia in the posterior neck can be considerable. Use the deep fascia layer exposed by the upper back flap of skin as a guide to following the layer into the neck.

17. As you reflect, extend the superior midline incision along the neck up to the external occipital protuberance.
    (Figure105c)

18. From the end of the incision make another 'T' incision along the cranial incision lines towards the mastoid processes.
    (Figure105c)

19. Reflect the neck skin flap laterally to approximately 2-3cm from the position of the mastoid process (just behind the ear).
    (Figure105c)

Reflect skin only from the posterior neck.

Do not reflect skin from the lateral region of the neck as that may damage structures which will be examined later in the course.

20. Return to your mid-back horizontal incision and make a vertical incision extending several inches inferiorly along the midline of the lower back. 
    (Figure105d)

21. Using hemostats grasp the exposed corner of skin and begin reflecting the lower back skin flap inferiorly and laterally following the plane between the hypodermis and deep fascia.
    (Figure105e)

The thickness of the fascia as you approach the lumbar region of the back can be considerable. As with the neck dissection, use the deep fascia layer exposed by the upper back flap of skin as a guide to following the layer inferiorly along the mid-back.

As you are separating the fascial planes to reflect the skin you may observe cutaneous nerves penetrating through the muscles (Netter183). These are typically easiest to observe along the lower back in the region below the scapula.

These cutaneous nerves are regularly spaced one per vertebral level and carry information to/from the dermis. Sensory innervation of the skin thus forms a series of 'bands' circumferentially around the body known as dermatomes. (Netter171) 

Cutaneous nerves will be easiest to find if using a blunt dissection separation technique. Fascia normally separates easily and the cutaneous nerves are more difficult to break.

21. Extend the midline incision inferiorly as needed to your marked lumbar incision line.
    (Figure105e)

22. Make horizontal incisions along your lumbar incision line and reflect the lower back skin flaps laterally to approximately the mid-axillary line.
    (Figure105e)

23. Return to the midline and continue your vertical incision extending several inches inferiorly along the midline over the lumbar region of the back. 
    (Figure105f)

24. Extend this midline incision inferiorly to your sacral incision line while reflecting the lumbar skin flap.
    (Figure105g)

The thickness of the skin/superficial fascia in the lumbar region varies considerably, in a well nourished individual it can be inches thick.

At the midline of the lumbar back look for a sheet of pale fascia that has a 'glassy' appearance to it. This is the surface of the thoracolumbar fascia. The thoracolumbar fascia is a dense connective tissue anchoring all of the muscles in this region. Functionally, this is the inferior/midline 'tendon' of the back muscles.

If you end up slightly shallow it will not affect the dissection as the thoracolumbar fascia will be cleaned further for examination later.

As with other regions of the back, as you reflect skin from the lumbar region you may encounter cutaneous nerves penetrating through the muscles (Netter183). As the thoracolumbar fascia is very thick, these nerves emerge from a more lateral location than the ones in the upper back.

25. Make horizontal incisions along your sacral incision line so that you can reflect the lumbar skin flaps laterally to approximately the mid-axillary line.
    (Figure105g) (Figure106)

26. Using forceps, scissors and/or your scalpel, clean the deep fascia from the two superficial muscles of the back, the trapezius and latissimus dorsi muscles.
    (Netter180) (Photo1001) 

It is not necessary to fully clean the muscles, which would be overly time consuming. Just clean fascia sufficiently to appreciate the position, shape, and orientation of the fibers comprising each muscle.

Trapezius muscle (Photo1002): Trapezius is a large triangular shaped muscle that extends from the base of the skull (external occipital protuberance) laterally along the spine of the scapula and back inferiorly to the lower thoracic vertebra.

Observe that the superior fibers of the trapezius muscle, fibers superior to the spine of the scapula, orient superiorly and medially into the neck. In contrast, the inferior fibers of the trapezius muscle, those inferior to the spine of the scapula, orient inferiorly and medially towards the midline of the back.

At the midline the left and right trapezius muscles attach to the tips of the vertebral spinous processes and the supraspinous ligament spanning those processes. In the neck the midline attachments anchor into the ligamentum nuchae.

Latissimus dorsi muscle (Photo1004): This large flat muscle extends superiorly from the lumbar vertebra to connect to the upper limb (its attachment to the humerus bone will be studied in a later section). Latissimus dorsi is partly covered in the mid back by the inferior edge of the trapezius muscle.

Thoracolumbar fascia (Photo1004): Observe that the inferior aspect of the latissimus dorsi muscle ends in a midline aponeurosis (flat tendon). This forms part of the thoracolumbar fascia anchoring all of the muscles in this region. It has the appearance of a glassy white sheet anchoring to the pelvis, sacrum and lumbar spinous processes before continuing over gluteal muscles as the gluteal aponeurosis.

27. Force your fingers or a blunt tool under the inferolateral edge of the trapezius muscle to mobilize that border from the underlying tissue.

28. Lift the inferolateral edge of the trapezius muscle and cut through the muscle as close as possible to the attachment along the spine allowing you to reflect part of the muscle superiorly.
    (Figure107) (Netter180) (Photo1003)

Reflect only the lower half of trapezius as far as necessary to expose the superior edge of latissimus dorsi (this will be approximately at the level of the inferior angle of the scapula).

Do not cut the trapezius muscle at any point superior to the inferior angle of the scapula as this may damage the rhomboid muscles which we will examine later in the course.

A good technique for separating a muscle attachment of this type is to insert one blade of the scissors just deep and lateral to the attachment and cut upward.  Scissors are important surgical tools, preferred over scalpels for most precision tasks, as they will only cut material between the blade avoiding inadvertent damage to the underlying muscles.

29. To reflect the latissimus dorsi muscle, force your fingers or a blunt tool under the superior edge of the latissimus dorsi muscle mobilizing the muscle from underlying tissue.

It is common for part of the latissimus dorsi muscle to attach to the inferior angle of the scapula (approximately half of all individuals will have some latissimus dorsi muscle or fascia attaching there).  If this is the case, do not try to detach it from the scapula, but modify the steps below to reflect the muscle laterally  as far as the scapular attachment point.

30. Lift the superior edge of the latissimus dorsi muscle and cut through the muscle as close as possible to the attachment along the spine allowing you to reflect the muscle laterally.
    (Figure107) (Netter180) (Photo1005)

Cut and reflect at the same time to ensure that you are only cutting through the latissimus dorsi muscle.

31. Reflecting latissimus dorsi exposes the thin serratus posterior inferior muscle.
    (Netter180) (Photo1005)

Observe that the fibers of the serratus posterior inferior muscle course approximately horizontally from medial to lateral. The msucle can be very thin with tight adherence to the latissimus dorsi muscle. If you do not see a distinct serratus posterior inferior muscle check to see if it was reflected along with the latissimus dorsi muscle.

The serratus posterior inferior muscle is a secondary muscle of respiration (only engaged during heavy breathing).

32. Cut serratus posterior inferior close to the midline and reflect the muscle laterally.  

33. Reflecting the latissimus dorsi and serratus posterior inferior muscles exposes the intrinsic (or true) deep back muscles underneath.
    (Netter181) (Photo1006)

The true back muscles act on the vertebral column and ribs and comprise two major muscle groups, the erector spinae and transversospinalis muscle groups. The fibers of the deep back muscles run vertically from inferior to superior.

34. The first group exposed by reflection of latissimus dorsi and serratus posterior inferior muscles is the erector spinae group.
    (Netter181) (Photo1006)

The erector spinae group of muscles consists of 3 muscular columns that extend from the base of the skull down to the pelvis embedding into the thoracolumbar fascia. 

Isolate each of the muscles below and examine their orientation. Separating these muscles can be somewhat difficult, particularly with the tight attachments the spinalis muscle makes to the spinous processes.  (Photo1010)

The erector spinae muscles are the:

Iliocostalis muscle (lateral, Photo1009): This muscle lies lateral to the longissimus muscle embedded into the thoracolumbar fascia and has 6-7 distinct tendons that insert into the lower 6-7 ribs.

Longissimus muscle (intermediate, Photo1008): The largest of the erector spinae muscles forms a muscular column immediately lateral to the spinalis muscles (and commonly fusing into the spinalis group). The muscle attaches into the thoracolumbar fascia and attaches fibers into the transverse processes of all the vertebrae.

Spinalis muscle (medial, Photo1007): These are formed by a column of muscles and tendinous insertions along the spinous processes of the vertebra. The lateral edge of the spinalis muscle commonly blends with the edge of the larger longissimus muscle. 

The erector spinae back muscles also continue up into the neck, but we will not be dissecting into that area specifically.

35. The second group of muscles are the deeper transversospinalis group. We will not be studying this group in any detail, but take a moment to review your atlas on their basic organization.
    (Netter182)

The transversospinalis group of muscles lie deep in the groove between vertebral spinous processes and laminae. These consist of three muscle groupings; semispinalis, multifidus and rotatores.

The muscles form a 'Christmas tree' appearance connecting the spinous process of a superior vertebra with the transverse process of a more inferior vertebra.

There is some controversy amongst textbooks about the relative prevalence/abundance of each of these muscles in the different regions of the spinal column. This is a nuance we do not need to consider.

37. Before completion of todays lab, check that the power tool battery is on the charger on the shelf at your station.

If a battery is on the tool, detach the battery and return it to your charger.

There is significant bone cutting in the next laboratory and this will ensure fully charged batteries are available for use.

38. When your study is complete, remove the wooden block from under the donor and return it to the foot of the shelf below your table.

LIGHTS REMINDER

Please remember to turn off the surgical lights at your station at the end of a session. This both protects the bulbs for longevity and saves electricity.

DONOR CARE REMINDER

You should moisten dissection surfaces as required to keep the surfaces from dehydrating. Dehydration will significantly increase the difficulty of your dissection and may destroy the structures you need to examine.

At the end of each dissection session, replace any reflected tissue flaps and cover the dissection area with the moist cloth,  close the inner plastic lining with a couple of hemostats, zip up the white bag, and neatly cover the donor with the blue drape cloth. 

Check that excess fluid hasn't accumulated in corners of the white bag and that edges of the while bag do not hang over the edge of the table. If this is the case, lift to return the fluid to the central drain and/or tuck the white bag in closer to the donor so that it will not leak over the table edge to the floor.

Proper care of your donor is training for patient care and a display of respect for the donation that this individual has given to provide you this unique anatomy opportunity.

CHECKLIST

Skeletal Structures

Scapula
    Acromion
    Spine
    Superior angle
    Inferior angle
    Vertebral border

Pelvic bone
    Iliac crest
    Posterior superior iliac spine

Vertebra
    Spinous process
    Vertebra prominens

Skull
    External occipital protuberance
    Mastoid process

Soft Structures

Skin
    Epidermis
    Dermis
    Hypodermis (superficial fascia)
    Deep fascia

Thoracolumbar fascia

Trapezius muscle

Latissimus dorsi muscle

Serratus posterior inferior muscle

Erector spinae muscles
    Spinalis muscle
    Longissimus muscle
    Iliocostalis muscle