In the next few lectures we will discuss the upper extremity, broken down further by

region, from proximal to distal: shoulder, axilla, brachium, cubital fossa/elbow,

antebrachium and wrist/hand.

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Generally speaking, the stability of the upper extremity has been sacrificed for
mobility. The lower extremity is involved in weight-bearing and motility, and the
opposite is true of it (i.e. some mobility sacrificed for stability).
The great freedom of movement enjoyed by the upper extremity is a consequence
of the shallow, ball-and-socket glenohumeral joint plus the conceptual
scapulothoracic joint – this “joint” is not an anatomical joint, but real movements of
elevation/depression, protraction/retraction, and superior/inferior rotation all take
place between the deep surface of the scapula and the posterolateral rib cage. We’ll
see how the sternoclavicular joint movement is coupled to scapular movements.
For maximal efficiency of the hand, that is, it’s characteristic abilities to grasp and
manipulate, more proximal joints must place it in the proper position (both fluid and
static).

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This is an overview still. General patterns: muscles are compartmentalized by deep
fascial coverings – the brachial and antebrachial fascia, septa which blend to
periosteum of the long bones, and an interosseous membrane.
Nerve distribution will be discussed later, but understanding the brachial plexus
and the distribution of C5-T1 nerve fibers will allow for proper physical examinations
of the upper extremity.
The blood supply is via the axillary artery. Veins are more variable in general, but
those that are deep accompany the arteries; those superficial are in the loose
connective tissue layer, immediately deep to skin.

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The superior appendicular skeleton, or pectoral girdle consists of the scapula and
clavicle; this bony brace is attached to the axial skeleton at only one point, the
sternoclavicular joint, and this allows for great mobility.

The axioappendicular muscles support, stabilize and move the pectoral girdle.

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The scapula is a triangular, flat bone. It is characterized by its coracoid process,
glenoid cavity, acromion, spine and three fossae: supraspinous, infraspinous and
subscapular. On the superior border, near the base of the coracoid process is the
scapular notch – the transverse ligament of the scapula runs over this notch,
making it an enclosed “tunnel” of short distance.
See also Fig. 3.5 on p.145 in text.

The humerus (Figs.3.3 & 3.6 on pp.144 and 146) is the only bone of the arm. It is
a typical long bone. It has a head and neck, and an expanded superolateral portion,
the greater tubercle. The intertubercular groove intervenes between the greater and
lesser tubercles. At the distal end, there is an expanded, flattened area, the humeral
condyle, with bumps on either side – the medial and lateral epicondyles. There are
fossae to accommodate parts of the forearm bones when the elbow joint is at
extremes of movement.

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The clavicle has a double curvature in the horizontal plane. Its medial half is convex
anteriorly – its lateral half, concave anteriorly. It (1) forms a strut, keeping the arm and
scapula away from the body during movements, (2) provides protection for neurovascular
structures passing from the thorax to the upper limb and (3) transmits shocks from the limb
to the axial skeleton. Because it is so moveable, the “scapulothoracic joint” can move as
well.
The sternal end articulates with the manubrium of the sternum at the sternoclavicular
joint. The acromial end articulates with the acromion of the scapula at the
acromioclavicular joint.
The superior surface is smooth. The inferior surface is characterized by several markings:
1)the conoid tubercle – for attachment of the conoid ligament (part of the coracoclavicular
ligament)
2)the trapezoid line – for attachment of the trapezoid ligament
3)the subclavian groove – for attachment of the subclavius m.
4)the impression for the costoclavicular ligament – a roughened portion medially for
attachment of the costoclavicular l.

Clavicular fracture (p.684) – very commonly fractured bone from force on outstretched
arm, or at the shoulder. Fracture usually occurs at junction of middle and lateral thirds of the
bone. The medial part is drawn superiorly by SCM and trapezius cannot support the limb,
so it sags.

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Each of these joints plays a role in determining upper limb mobility and often they
are all moving together.

The scapulothoracic joint is not a real, articulating joint. It is “physiologic” or

conceptual, and involves the real movement of the anterior surface of the scapula
gliding across the surface of the ribs.
The approximate ratio of movement in elevation of the shoulder is 2 degrees at the
glenohumeral for every 1 degree at the scapulothoracic joint. This is termed the
scapulohumeral rhythm. See Figs. 3.91 and 3.92 on p.264-265 in text.

There is a figure (TABLE 3.5, p172) in the book summarizing scapular movements
– it is worth spending some time here!

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The sternoclavicular joints are the only points of attachment for the upper limbs
to the trunk. The saddle-type joint functions as a ball-and-socket joint. The
clavicle is the radius through which the shoulder moves (on an arc) from the SC
joint.

The articular disc is strong and attached to the sternoclavicular ligaments,

thickened portions of the joint capsule, which support the joint anteriorly and
posteriorly. It helps to absorb force/shocks from the upper extremity. Dislocations
are rare, but fractures, particularly at the junction of the middle third and lateral third
of the surface of the clavicle are common.
The interclavicular ligament supports the joints as well, attaching the medial ends
of the clavicles with the superior border of the manubrium of the sternum.
The joint is mobile superiorly to about 60 degrees and anterior/posteriorly (i.e.,
protraction/retraction of scapula) to about 30 degrees.
The costoclavicular ligament is shown anchoring the clavicle to the 1st rib. It limits
the amount of elevation of the clavicle.

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The acromioclavicular joint is a plane-type synovial joint. The bones are
separated by an incomplete wedge of cartilage, the articular disc.
The capsule is loose, and weakly supported on its superior aspect by some of the
fibers of the trapezius m.

*There are NO MUSCLES attaching the ends of the bones to move the joint.
Movement only occurs when the scapula moves secondary to contraction of
axioappendicular muscles.

AC joint dislocation (p.283) From trauma. The AC ligament is not as strong as the
CC. A “separation” occurs when the CC ligament is ruptured as well – the humeral
head falls away from the glenoid, the acromion is more prominent and the distal
clavicle may appear elevated.

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Acromioclavicular ligament strengthens the joint superiorly.
There are extrinsic ligaments that are important to maintaining the joint though: the
coracoclavicular is actually two ligaments – the conoid, more medially located and
more posterior on the coracoid (at the root) and the trapezoid. These are very
strong ligaments that anchor the clavicle to the scapula. They also suspend the
scapula from the strut (clavicle).

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The humeral head has a small area of articulation with the shallow glenoid cavity –
this arrangement allows it the MOST FREEDOM OF MOVEMENT OF ALL THE
JOINTS IN THE BODY. The fibrocartilage ring surrounding the glenoid cavity is the
glenoid labrum, and it helps to deepen the cavity. The rotator cuff muscles though
are largely repsonsible for holding the humeral head in the joint.
The joint capsule is a loose fibrous capsule that attaches medially to the margin of
the glenoid and laterally to the anatomical neck of the humerus.
The capsule has two deficits: one for the passage of the tendon of the long head of
the biceps brachii m. and the other as a communication with the subscapular bursa.
The subscapular bursa directly communicates with the glenohumeral joint cavity.
Its function is to protect the subscapularis tendon from excessive wear.
Likewise, the subacromial bursa (aka the subdeltoid bursa) protects the
supraspinatus tendon from wear against the inferior surface of the acromion.
Glenohumeral joint dislocation (p.284) From trauma – most displace inferiorly,
though they are referred to as “anterior” or “posterior” according to their relative
position with the long head of the triceps on the infraglenoid tubercle.

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The three glenohumeral ligaments strengthen the joint capsule anteriorly. They
are evident on the internal aspect of the capsule.
In the bottom image, they are traced in YELLOW – the superior, middle and inferior
glenohumeral ligaments.
The coracohumeral ligament strengthens the capsule superiorly. It is outlined in
red above, and at the 1 o’clock position in the bottom image.
The transverse humeral ligament bridges over the intertubercular groove and
holds the tendon of the long head of the biceps in place.
The coracoacromial arch is an extrinsic structure and consists of the bony parts
and the coracoacromial ligament. It prevents the humeral head from becoming
displaced from the joint in a superior direction.
Glenoid labrum tears (p.285) From throwing – usually in the anterosuperior aspect
of the labrum. There usually is pain with the throwing motion, and abduction/lateral
rotation may cause a popping or snapping.

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There are 4 anterior muscles that act to move the pectoral girdle: pectoralis major,
pectoralis minor, subclavius and serratus anterior.
Winged scapula (p.179) – results from paralysis of serratus anterior m./injury to
long thoracic n. The nerve is not protected when the arm is abducted. The medial
edge of the scapula protrudes posteriorly, appearing like a wing, especially when
the patient leans forward against a wall. The arm cannot abduct past the horizontal
because the glenoid cannot rotate superiorly.

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The muscles shown in isolation from Fig. 3.21 on p.168
Pectoralis major has 2 heads, a clavicular head (which can flex the humerus when
acting alone) and a larger sternocostal head (which extends the humerus from a
flexed position). Together, they provide powerful ADDUCTION and MEDIAL
ROTATION for the arm.
Pectoralis minor draws the scapula anteriorly and inferiorly against the thoracic
wall.
Subclavius anchors/depresses the clavicle.
Serratus anterior protracts the scapula and the inferior fibers rotate the scapula so
that the glenoid tips superiorly.

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Table 3.3 on p.168 in text.
The medial and lateral pectoral nerves are named from where they emerge from the
brachial plexus, not their relative positions in the body.

A generalization we can make is that the proximal muscles of the upper extremity
are predominantly innervated by more cranial (or superior) spinal nerves of the
brachial plexus.

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We have already discussed the superficial and deep posterior axioappendicular
muscles because of their location on the back.

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These are the intrinsic shoulder muscles, or scapulohumeral muscles: deltoid,
teres major and the muscles of the rotator cuff = supraspinatus,
infraspinatus, teres minor and subscapularis.

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The deltoid muscle is thick and powerful. It has both UNIPENNATE (anteriorly and
posteriorly) and MULTIPENNATE (middle part) fiber groupings.
All parts working together results in arm ABDUCTION. The anterior and posterior
portions steady the arm while abduction occurs. When the arm is fully adducted, the
fibers only pull superiorly, along the vertical axis, thus, the deltoid cannot initiate
abduction. (Supraspinatus does to 15 degrees).
The anterior fibers assist pectoralis major in flexing the arm. They also medially
rotate the arm.
The posterior fibers assist latissimus dorsi in extending the arm. They also can
laterally rotate the arm.
The deltoid also acts to hold the humeral head in place, preventing inferior slipping
of the humeral head from the glenoid cavity.

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Teres major (cut) is a thick, round muscle. It adducts and medially rotates the arm.
It also plays a role in stabilizing the humeral head.
The ROTATOR CUFF muscles are the supraspinatus, infraspinatus, teres minor
and subscapularis. Their principal function is, with their tendons, to form a cuff
around the humeral head and keep it in the glenoid cavity.
All but the supraspinatus are rotators of the arm (singly it abducts). The
infraspinatus and teres minor are lateral rotators, the subscapularis, a medial
rotator of the arm (or humerus/GH joint).
Rotator cuff injuries (p.284) Usually due to repetitive motion (baseball,
weightlifters, swimmers). The supraspinatus is vulnerable and commonly involved.
Repetitive trauma can result in inflammation and tendinitis.

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Table 3.6 on p.174 in text.
Note that although the peripheral nerves are varied, C5 and C6 fibers dominate.

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QUADRANGULAR – the posterior circumflex humeral a. and axillary n. pass
through
Boundaries: Superiorly, the inferior border of teres minor m.; inferiorly, the superior
border of teres major m.; laterally, the surgical neck of the humerus and medially,
the lateral border of the long head of the triceps brachii m.
TRIANGULAR – circumflex scapular artery lies deep
Boundaries – teres minor m., teres major m. and medial border of long head of
triceps brachii m.
TRIANGULAR INTERVAL – radial n. and profunda brachii a. lie deep
Boundaries – inferior border of teres major m. and lateral/long heads of the triceps
brachii m.

Axillary nerve injury (p.180) – humerus fractures at the surgical neck, dislocations
of the humeral head and incorrect crutch use can all lead to damage. The deltoid
will atrophy and leave a hollow just inferior to the acromion. There is lateral,
proximal anesthesia also.

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