PROCEDURE

a) On the scapula locate the vertebral border and follow that superiorly to the superior angle and inferiorly to the inferior angle.

b) On the superior aspect identify the spine and follow that laterally to the acromion process.
(iPhoto6002)

c) The smaller space superior to the spine of the scapula is the supraspinous fossa and the larger space inferior to the spine is the infraspinous fossa.

d) The large notch deep to the spine/acromion is the greater scapular notch connecting the supraspinous fossa and infraspinous fossa. The smaller notch on the superior border of the scapula is the suprascapular notch. (iPhoto6002)

The suprascapular nerve passes over the scapula through the suprascapular notch, provides branches innervating the deep side of the supraspinatus muscle, curves around the greater scapula notch, and innervates the deep side of the infraspinatus muscle. The nerve is accompanied by the suprascapular artery and vein. (Figure614) (Figure643)

e) On the back of the skull identify the external occipital protuberance at the midline.

f) On the proximal end of the humerus identify the head and neck.

g) View the humerus, scapula and clavicle in their anatomic positions and observe the arrangement of these three bones.

2. Place a wood block under the chest to make the posterior shoulder region easier to work upon.
    (Figure101a)

3. Working from the midline laterally, reflect skin from the posterior neck, posterior shoulder and along the posterior arm.
    (Figure611)

Remove skin from the neck as far anteriorly as the mid-lateral neck (i.e. approximately in line with the mastoid process and ear). This point lines up with the prior skin removal from the anterior side.

Remove skin over the lateral shoulder proceeding a few centimeters around to the anterior side.

Remove skin from the posterior side of the arm distally to the elbow. The skin should separate easily along the plane between the hypodermis and the brachial fascia.

The upper extremities are encased in a fascial sheath. This is the brachial fascia on the arm and the antebrachial fascia on the forearm. These are equivalent to the fascia lata and crural fascia of the lower extremities. (Figure616)

An intermuscular fascial septum separates the arm into an anterior compartment and a posterior compartment. As with the lower extremities, compartments are an important organizational principle for the upper limbs as muscles within generally share a nerve and vascular supply. (Figure616)

We will be opening the brachial fascia later in the lab so if you inadvertently cut the fascia it will not affect the dissection.

4. Identify the trapezius muscle partially dissected in the section examining the back and trace the shape of the muscle.
    (Netter413) (Photo1002)

Trapezius attaches superiorly in the neck and along the length of the vertebral column. Laterally and anteriorly it attaches to the lateral third of the clavicle and the acromion process. Posteriorly it attaches along the spine of the scapula.

5. Insert fingers or a blunt probe below the inferolateral border of the trapezius muscle working your way superiorly until you are blocked by the attachments to the spine of the scapula.
    (Figure612a) (Netter413) (Photo6111)

The fascia along this edge can be strong in some individuals and you may need scissors or a scalpel to gain access under the muscle.

6. Use scissors or a scalpel and cut the attachments of the trapezius muscle from the inferior side of the spine and acromion of the scapula working from lateral to medial.
    (Figure612a) (Netter413) (Photo6112)

Cut parallel to the spine of the scapula and close to the bone.

The infraspinatus muscle deep to the trapezius muscle is oriented parallel to the spine of the scapula. Thus, do not worry about going too deep in the cut parallel to the spine of the scapula as that will not significantly disrupt deeper structures.

7. Reflect the lower trapezius muscle medially over to the midline, leaving it attached only along the spinous processes.
    (Figure612b) (Netter413) (Photo6113)

As you pass to the region between the vertebral border of the scapula and spinous processes of the vertebral column, exercise care when lifting and cutting trapezius so as to minimize inadvertent cuts through the rhomboid group of muscles deep to the trapezius muscle.

8. Push fingers or a probe deep to the cut edge of the superior part of the trapezius muscle near the midline to mobilize a space deep to the muscle.
     (Netter413) (Photo6114)

Stay just deep to the trapezius muscle so as to mobilize between trapezius and the rhomboid muscle group laying immediately deep to the trapezius muscle.

9. Use scissors or a scalpel and cut the attachments of the trapezius muscle from the spinous processes as high as partly into the neck.
    (Figure612c) (Netter413) (Photo6115) (Photo6116)

This should leave the superior part of the trapezius muscle separated from the spinous processes through to the neck.

10. Working from medial to lateral, using scissors or a scalpel, cut through the attachments of the trapezius muscle to the superior side of the spine and acromion of the scapula as you reflect the muscle.
    (Figure612d) (Netter413) (Photo6117) (Photo6119)

Continue laterally around the acromion stopping at a point just anterior to the shoulder where the clavicle is located.

This should leave the inferior part of the trapezius muscle attached to the spinous processes and the superior part of the muscle attached to the clavicle and the occipital protuberance of the skull.

Trapezius is innervated by the accessory nerve (cranial nerve XI). Any nerve bundles on the deep surface of the muscle are branches of the accessory nerve spreading out across the muscle.

11. Examine the rhomboid muscle group attached to the medial edge of the scapula.
    (Netter183) (Netter413) (Photo6118) (Photo6119)

The rhomboid major and rhomboid minor muscles attach to the medial border of the scapula inferior to the spine. 

These muscles project superomedially to attach to the spinous processes of vertebra C7-T1 (rhomboid minor) and T2-5 (rhomboid major).

The separation between rhomboid major and minor in many individuals is indistinct. In that case, the upper fibers heading to the neck will be the rhomboid minor and the lower fibers spanning to thoracic vertebrae the rhomboid major.

12. Using blunt dissection define the borders of the deltoid muscle and its attachments to the lateral third of the clavicle, acromion process, and the lateral region of the scapula spine.
    (Netter413) (Photo6064)

The deltoid muscle 'wraps' around the lateral shoulder (scapula to clavicle) and converges to insert on the lateral side of the proximal humerus. 

Due to the extensive origin, the muscle can flex, extend or abduct the arm (humerus). Other muscles also flex/extend the arm so that function is redundant, but the deltoid muscle is the primary abductor of the arm from 15-90 degrees with no backup in that range.

13. Force a blunt probe deep to the posteromedial edge of the deltoid and cut through the attachments along the spine of the scapula.
    (Figure645) (Photo6064) 

Progressively work your way around the spine of the scapula, acromion and lateral clavicle cutting close to the bone as you detach the deltoid muscle.

14. Gently reflect the deltoid muscle laterally over the head of the humerus, taking care not to rupture the neurovascular bundle entering the deep surface of the muscle.
    (Figure613) (Netter422) (Photo6062) (Photo6018)

15. Blunt dissect into the fascia on the deep surface of the deltoid to find branches of the neurovascular bundle entering the deep surface of the deltoid muscle.
    (Figure613) (Netter422) (Photo6017)

These are the axillary nerve innervating the deltoid and posterior humeral circumflex artery (and vein) supplying blood to the muscle.

16. Follow the nerve/vessels proximally where they pass through a roughly quadrangular space between muscles.
    (Figure613) (Netter422) (Netter418) (Photo6017)
    (iPhoto6001)

Push your finger parallel to the nerve/vessels into the quadrangular space and widen it slightly to see the muscular boundaries of the space.

This quadrangular space is between two heads of the triceps brachii muscle (the long and lateral heads) marking the medial and lateral sides of the space repsectively. The superior side is formed by the teres minor muscle and the inferior side by the teres major muscle.

This quadrangular space allows nerves (axillary) and vessels (posterior circumflex humeral) from the anterior side to pass to the posterior side of the shoulder into the deltoid muscle.

On the way to the quadrangular space, the axillary nerve passes close to the humerus bone. Thus, fractures at the proximal end of the humerus put the axillary nerve at risk. This is the A of the ARM mnemonic ("A"xillary nerve for proximal fractures, "R"adial nerve for mid arm fractures, and "M"edian nerve for distal humeral fractures).

17. Identify the long head of triceps brachii, which made the medial border of the quadrangular space opened in the previous step. 
    (Figure613) (Netter422) (Netter418) (Photo6062)

Trace the long head of triceps brachii superiorly and observe that it passes anterior (deep) to the teres minor muscle.

18. Remove any remaining skin and superficial fascia from the posterior arm to just past the elbow joint.

Unlike the anterior side, the posterior superficial fascia contains only small veins that pass to the anterior side before connecting to the cephalic and basilic veins.

19 Using scissors make a longitudinal incision in the posterior surface of the brachial fascia from the level of the teres minor muscle down to the olecranon of the ulna.

You may find it helps to insert a blunt probe deep to the brachial fascia and lift the fascia providing an edge that can be cut.

20. Use your fingers to spread open the brachial fascia working laterally until your fingers are stopped by a fascial barrier, the lateral intermuscular septum.
    (Figure616) (Photo6120)

The intermuscular septum divides the arm into an anterior and posterior compartment.

The posterior compartment of the arm contains the large triceps brachii, an extensor muscle. This compartment is innervated by the radial nerve and receive blood from the profunda brachii artery.

21. Repeat the process separating the brachial fascia medially until your fingers are stopped by the medial intermuscular septum such that you have fully exposed the triceps brachii muscle.
    (Figure616) (Photo6120)

22. Spread the long and lateral heads of triceps brachii and observe that the two heads converge partway distally along the arm.
    (Figure613) (Netter422)

The triceps brachii muscle has three proximal attachments, or heads, the 'tri' in triceps. The long head is attached to the scapula, the lateral head is attached to the posterior surface of the proximal humerus and the medial head is deep attached to the posterior surface of the distal humerus.

All three heads converge distally to a common tendon that inserts onto the olecranon process of the ulna.

23. Use a probe or scalpel to split the gap between the long head and lateral heads of the triceps brachii muscle distally to approximately a third to halfway along the arm. 
    (Figure619a) (Netter422) (Photo6121) (Photo6122)

This exposes the medial head that is mostly covered by the lateral and long heads. The medial head is small and less well defined, so it may not distinguishable in all individuals as a discrete muscle bundle.

Any muscle fibers attaching deep along the posterior humerus are likely fibers of the medial head.

24. In the space between the lateral and long heads, dissect against the posterior surface of the humerus where the radial nerve and profunda brachii artery pass into the posterior compartment. 
    (Figure619a) (Netter422) (Photo6063)

The radial nerve and profunda brachii artery pass directly against the humerus in a shallow spiraled groove in the bone called the radial groove. Thus, at first appearance you won't see the neurovascular bundle and you need to dig a little into the fascia against the humerus bone. 

The radial nerve and profunda brachii vessels (artery and vein) supply the posterior compartment of the arm and the forearm.

The close association of the radial nerve as it passes across the humerus in the radial groove makes the nerve subject to risk in this region (i.e. with mid-humeral fractures....the "R" in the ARM mnemonic for nerve fracture risk).

25. Cut through the infraspinatus fascia attached to the inferior edge of the spinous process of the scapula such that it can be lifted away from the underlying infraspinatus muscle.
    (Figure651) (Photo6123)

The muscles of the rotator cuff (supraspinatus, infraspinatus, teres minor, and subscapularis) are surrounded by a strong fascia anchored to the bone of the scapula. To observe the muscles, this needs to be excised.

26. Continue excising the fascia layer working inferiorly along the vertebral border of the scapula.
    (Figure651a) (Photo6123a)

It is common for the infraspinatus fascia to be adherent to the muscle fibers of infraspinatus, and these may need to be transected if present to fully expose the muscle itself. (Photo6123b)

27. Remove the infraspinatus fascia cutting any remaining attachments and trace the borders of the infraspinatus muscle (present inferior to the scapula spine and superior to teres minor/major).
    (Figure613) (Netter417) (Photo6020)

28. Using a blunt probe separate the edges of the infraspinatus and teres minor muscles.
    (Figure613) (Netter417) (Photo6020)

Infraspinatus and teres minor have similar orientation fibers and frequently an indistinct boundary and/or partially blended edges.

Teres major is buried in fascia and difficult to visualize clearly, thus we will not be separating out this muscle specifically.

29. Return to the scapula and trace the borders of the supraspinatus muscle (located in the supraspinatus fossa).
    (Figure613) (Netter417) (Photo6020)

The supraspinatus is also commonly contained in a tight supraspinatus fascia anchored to bony edges of the spine of the scapula.

Thus, you may need to perform a similar fascia removal process just performed to expose the infraspinatus muscle in order to to expose the supraspinatus muscle itself.

PROCEDURE - GLENOHUMERAL JOINT

30. Follow the distal end of the infraspinatus muscle to where the aponeurosis of the muscle blends into the capsule of the shoulder.
    (Figure613) (Netter417) (Photo6065)

The flat tendons of supraspinatus, infraspinatus, teres minor (and subscapularis on the deep side of the scapula) all fuse into the capsule of the shoulder joint and attach to the tuberosities of the humerus bone. 

The flat tendons of these four muscles form the rotator cuff around the glenohumeral joint, one of the most common locations for upper limb injury.

31. Place fingers against the rotator cuff just inferior to the acromion and lift/move the donor arm so that you can feel the movement of the head of the humerus relative to the scapula.
    (Figure646) (Netter412) (Netter415) (Photo6066)   

It will help to have one of the team press on the vertebral border of the scapula to keep the scapula stationary while moving the arm.

You should feel the relative movement of the bones identifying the approximate position of the glenohumeral joint as you move the arm.

The glenohumeral joint is a multi-axis ball & socket joint with a joint capsule that provides only weak support. The glenohumeral joint is colloquially known as the shoulder joint.

The major support of the joint comes from the associated ligaments, overhanging acromion process, and insertions of the rotator cuff muscles. These all provide strong support superiorly, however, support is weaker anteroinferiorly. Thus, the joint is at most risk of dislocation in the anteroinferior direction.

32. On one limb only, cut deep (to the bone) along a superior to inferior line transecting through the supraspinatus, infraspinatus, and teres minor tendons.
    (Figure647) (Netter412) (Netter415) (Photo6067)

This cut line should be approximately where you felt the movement of the humerus and scapula forming the glenohumeral joint. The point is about 3-4cm medial from the lateral tip of the acromion.

As you make the cut you will see part of the smooth articulating surface of the head of the humerus come into view.

33. Rotate the upper limb medially (internal rotation) to spread open the joint and examine the interior surfaces.
     (Netter412) (Photo6068)

The joint does not need to be fully ruptured, just opened sufficiently to observe the interior structures.

Identify the glenoid labrum, which is a fibrocartilaginous rim around the margins of the glenoid fossa. Note how shallow the glenoid labrum/fossa are.

In contrast, the labrum of the hip joint forms a deep socket for hip stability. A shallow labrum provides the glenohumeral joint with a greater range of motion than the hip joint, but reduced stability leading to elevated risk of dislocation of the humerus.

The rotator cuff is a major stabilizer of the glenohumeral joint, but additional ligaments from the coracoid process also stabilize the joint. But we will not be studying these. 

CHECKLIST

Skeletal Structures

Scapula
    Acromion
    Spine
    Superior and inferior angles
    Vertebral border

Humerus
    Articular surface of the head

Clavicle

Soft Structures

Trapezius muscle

Rhomboid major muscle

Rhomboid minor muscle 

Latissimus dorsi muscle

Deltoid muscle

Triceps brachii
    Long head
    Lateral head
    Medial head

Teres minor

Supraspinatus muscle

Infraspinatus muscle

Axillary nerve

Posterior humeral circumflex artery

Profunda brachii artery

Radial nerve

Glenohumeral joint
    Rotator cuff
    Glenoid labrum
    Glenoid fossa