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SHOULDER
29. December.2012 Thursday
The shoulder is the region of upper limb attachment to the trunk.
Shoulder is the proximal segment of the limb that overlaps parts of the trunk (thorax and back) and lower lateral
neck. It includes the pectoral, scapular, and deltoid regions of the upper limb, and the lateral part (greater
supraclavicular fossa) of the lateral cervical region. It overlies half of the pectoral girdle. The pectoral
(shoulder) girdle is a bony ring, incomplete posteriorly, formed by the scapulae and clavicles and completed
anteriorly by the manubrium of the sternum (part of the axial skeleton).
The bone framework of the shoulder consists of:
 the clavicle and scapula, which form the pectoral girdle (shoulder girdle); and
 the proximal end of the humerus.
The superficial muscles of the shoulder consist of the trapezius and deltoid muscles, which together form the
smooth muscular contour over the lateral part of the shoulder. These muscles connect the scapula and clavicle
to the trunk and to the arm, respectively.
Joints
The three joints in the shoulder complex are the sternoclavicular, acromioclavicular, and glenohumeral joints.
The sternoclavicular joint and the acromioclavicular joint link the two bones of the pectoral girdle to each other
and to the trunk. The combined movements at these two joints enable the scapula to be positioned over a wide
range on the thoracic wall, substantially increasing "reach" by the upper limb.
The glenohumeral joint (shoulder joint) is the articulation between the humerus of the arm and the scapula.
Muscles
The two most superficial muscles of the shoulder are the trapezius and deltoid muscles. Together, they
provide the characteristic contour of the shoulder:
 trapezius attaches the scapula and clavicle to the trunk;
 deltoid attaches the scapula and clavicle to the humerus.
Both the trapezius and deltoid are attached to opposing surfaces and margins of the spine of the scapula,
acromion, and clavicle. The scapula, acromion, and clavicle can be palpated between the attachments of
trapezius and deltoid.
SUPERFICIAL POSTERIOR AXIOAPPENDICULAR (EXTRINSIC SHOULDER) MUSCLES
The superficial axioappendicular muscles are the trapezius and latissimus dorsi.
Trapezius
The superior fibers of trapezius, from the skull and upper portion of the vertebral column, descend to
attach to the lateral third of the clavicle and to the acromion of the scapula.
The superior and inferior fibers work together to rotate the lateral aspect of the scapula upward, which
needs to occur when raising the upper limb above the head. Movement to 180 degrees (elevation) is brought
about by rotation of the scapula upwards by the trapezius and serratus anterior (see “Movements of the shoulder
girdle” on page 7). The trapezius also braces the shoulders by pulling the scapulae posteriorly and superiorly,
fixing them in position on the thoracic wall with tonic contraction; consequently, weakness of this muscle
causes drooping of the shoulders.
Latissimus dorsi
This large, fan-shaped muscle passes from the trunk to the humerus and acts directly on the
glenohumeral joint and indirectly on the pectoral girdle (scapulothoracic joint). The latissimus dorsi extends,
retracts, and rotates the humerus medially (e.g., when folding the arms behind the back or scratching the skin
over the opposite scapula).
In combination with the pectoralis major, the latissimus dorsi is a powerful adductor of the humerus and
plays a major role in downward rotation of the scapula in association with this movement. It is also useful in
restoring the upper limb from abduction superior to the shoulder; hence the latissimus dorsi is important in
climbing. In conjunction with the pectoralis major, the latissimus dorsi raises the trunk to the arm, which occurs
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when performing chin-ups (hoisting oneself so the chin touches an overhead bar) or climbing a tree, for
example. These movements are also used when chopping wood, paddling a canoe, and swimming (particularly
during the crawl stroke).
DEEP POSTERIOR AXIOAPPENDICULAR (EXTRINSIC SHOULDER) MUSCLES
The deep posterior thoracoappendicular muscles are the levator scapulae and rhomboids. These
muscles provide direct attachment of the appendicular skeleton to the axial skeleton.
Levator scapulae
True to its name, the levator scapulae acts with the descending part of the trapezius to elevate the
scapula, or fix it (resists forces that would depress it, as when carrying a load. With the rhomboids and
pectoralis minor, the levator scapulae rotates the scapula, depressing the glenoid cavity (rotating the lateral
aspect of scapula inferiorly). Acting bilaterally (also with the trapezius), the levators extend the neck; acting
unilaterally, the muscle may contribute to lateral flexion of the neck (toward the side of the active muscle).
Rhomboid minor and major
The rhomboids retract and rotate the scapula, depressing its glenoid cavity. They also assist the serratus
anterior in holding the scapula against the thoracic wall and fixing the scapula during movements of the upper
limb. The rhomboids are used when forcibly lowering the raised upper limbs (e.g., when driving a stake with a
sledge hammer).
SCAPULOHUMERAL (INSTRINSIC SHOULDER) MUSCLES
The six scapulohumeral muscles (deltoid, teres major, supraspinatus, infraspinatus, subscapularis, and
teres minor) are relatively short muscles that pass from the scapula to the humerus and act on the glenohumeral
joint.All the intrinsic muscles but the deltoid and the subscapularis are muscles of the posterior scapular region.
Deltoid
The deltoid muscle is large and triangular in shape, with its base attached to the scapula and clavicle and its
apex attached to the humerus. It originates along a continuous U-shaped line of attachment to the clavicle and
the scapula, mirroring the adjacent insertion sites of the trapezius muscle. It inserts into the deltoid tuberosity
on the lateral surface of the shaft of the humerus.
The major function of the deltoid muscle is abduction of the arm beyond the initial 15° accomplished by the
supraspinatus muscle.
The deltoid muscle is innervated by the axillary nerve, which is a branch of the posterior cord of the brachial
plexus.
http://www.sciencelearn.org.nz/var/sciencelearn/storage/images/contexts/sporting-edge/sci-media/images/deltoid-muscles/14542-15-engNZ/Deltoid-muscles_full_size_portrait.jpg
Subscapularis
The subscapularis is a thick, triangular muscle that lies on the costal surface of the scapula and forms part of
the posterior wall of the axilla. It originates from the subscapular fossa on the anterior surface of the scapula
and attaches to the lesser tubercle of the humerus. The subscapularis is the primary medial rotator of the arm
and also adducts it. It joins the other rotator cuff muscles in holding the head of the humerus in the glenoid
cavity during all movements of the glenohumeral joint (i.e., it helps stabilize this joint during movements of the
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elbow, wrist, and hand). It is innervated by superior and inferior subscapular nerves of the brachial plexus.
http://www.coretherapy.com/images/fig_4.gif
POSTERIOR SCAPULAR REGION
The posterior scapular region occupies the posterior aspect of the scapula and is located deep to the
trapezius and deltoid muscles. It contains four muscles, which pass between the scapula and proximal end
of the humerus: supraspinatus, infraspinatus, teres minor, and teres major muscles.
The posterior scapular region also contains part of one additional muscle, the long head of the triceps brachii,
which passes between the scapula and the proximal end of the forearm. This muscle, along with other muscles
of the region and the humerus, participates in forming a number of spaces through which nerves and vessels
enter and leave the region.
The supraspinatus, infraspinatus, and teres minor muscles are components of the rotator cuff, which
stabilizes the glenohumeral joint.
Supraspinatus & infraspinatus
The supraspinatus and infraspinatus muscles originate from two large fossae, one above and one below the
spine, on the posterior surface of the scapula. They form tendons that insert on the greater tubercle of the
humerus. The tendon of the supraspinatus inserts on the superior facet of the greater tubercle.
The tendon of the infraspinatus passes inserts on the middle facet of the greater tubercle.
The supraspinatus initiates abduction of the arm. The infraspinatus laterally rotates the humerus.
http://www.daviddarling.info/images/rotator_cuff.jpg
Teres minor and teres major
The teres minor muscle is a cord-like muscle that originates from a flattened area of the scapula immediately
adjacent to its lateral border below the infraglenoid tubercle. Its tendon inserts on the inferior facet of the
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greater tubercle of the humerus. The teres minor laterally rotates the humerus and is a component of the rotator
cuff.
The teres major muscle originates from a large oval region on the posterior surface of the inferior angle of the
scapula. This broad cord-like muscle ends as a flat tendon that attaches to the medial lip of the intertubercular
sulcus on the anterior surface of the humerus. The teres major medially rotates and extends the humerus.
http://ncpad.com/get/images/strengthexercisehandouts/INTrotation_TERES_MAJOR.jpg
Long head of triceps brachii
The long head of triceps brachii muscle originates from the infraglenoid tubercle and passes somewhat
vertically down the arm to insert, with the medial and lateral heads of this muscle, on the olecranon of the ulna
The triceps brachii is the primary extensor of the forearm at the elbow joint. Because the long head crosses the
glenohumeral joint, it can also extend and adduct the humerus.
ROTATOR CUFF MUSCLES
Four of the scapulohumeral muscles (intrinsic shoulder muscles)—supraspinatus, infraspinatus, teres
minor, and subscapularis (referred to as the SITS muscles)—are called rotator cuff muscles because they form
a musculotendinous rotator cuff around the glenohumeral joint. The rotator muscles are short muscles which
covers and blends with all bu the inferior aspect of the shoulder joint. The supraspinatus, infraspinatus and
teres minor are inserted from above down into the humeral greater tubercle, and the subscapularis is inserted
into the lesser tubercle. All originate from scapula. All except the supraspinatus are rotators of the humerus;
the supraspinatus, besides being part of the rotator cuff, initiates and assists the deltoid in the first 15° of
abduction of the arm (See “Movements of the shoulder girdle” on page 7).
http://assets2.medhelp.org/adam/graphics/images/en/19622.jpg
The tendons of the SITS muscles blend with and reinforce the fibrous layer of the joint capsule of the
glenohumeral joint, thus forming the rotator cuff that protects the joint and gives it stability. The tonic
contraction of the contributing muscles holds the relatively large head of the humerus in the small, shallow
glenoid cavity of the scapula during arm movements.
Gateways to the posterior scapular region
Suprascapular foramen
The suprascapular foramen is the route through which structures pass between the base of the neck and the
posterior scapular region. It is formed by the suprascapular notch of the scapula and the superior transverse
scapular (suprascapular) ligament, which converts the notch into a foramen.
The suprascapular nerve passes through the suprascapular foramen; the suprascapular artery and the
suprascapular vein follow the same course as the nerve, but normally pass immediately superior to the superior
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transverse scapular ligament and not through the foramen.
http://www.e-algos.com/wp-content/uploads/2011/05/84611-91895-92672-92768.jpg
Quadrangular space
See the class notes of the “Axilla and brachial plexus”
Triangular space
page 2
Triangular interval
Because this space is below the inferior margin of the teres major, which defines the inferior boundary of the
axilla, the triangular interval serves as a passageway between the anterior and posterior compartments of the
arm and between the posterior compartment of the arm and the axilla. The radial nerve, the profunda brachii
artery (deep artery of arm), and associated veins pass through it.
Nerves
The two major nerves of the posterior scapular region are the suprascapular and axillary nerves, both of
which originate from the brachial plexus in the axilla.
Suprascapular nerve
The suprascapular nerve originates in the base of the neck from the superior trunk of the brachial plexus. It
passes through the suprascapular foramen to reach the posterior scapular region, where it lies in the plane
between bone and muscle. It innervates the supraspinatus muscle, then terminates in and innervates the
infraspinatus muscle. Generally, the suprascapular nerve has no cutaneous branches.
Axillary nerve
The axillary nerve originates from the posterior cord of the brachial plexus. It exits the axilla by passing
through the quadrangular space in the posterior wall of the axilla, and enters the posterior scapular region.
Together with the posterior circumflex humeral artery and vein, it is directly related to the posterior surface of
the surgical neck of the humerus.The axillary nerve innervates the deltoid and teres minor muscles. In addition,
it has a cutaneous branch, the superior lateral cutaneous nerve of the arm, which carries general sensation
from the skin over the inferior part of the deltoid muscle.
Arteries and veins
Three major arteries are found in the posterior scapular region: the suprascapular, posterior circumflex
humeral, and circumflex scapular arteries. These arteries contribute to an interconnected vascular network
around the scapula. Veins in the posterior scapular region generally follow the arteries and connect with vessels
in the neck, back, arm, and axilla.
Anastomosis in the shoulder
Formation of anastomosis around the surgical neck of humerus
(See for more info @ http://www.slideshare.net/ananthatiger/3-anastomosis-around-the-surgical-neck-of-humerus1)
Anterior circumflex humeral artery and posterior circumflex humeral artery are both branches of the third part
of the axillary artery.The posterior circumflex humeral artery anastomoses with anterior circumflex humeral
artery and also with branches from profunda brachii (a branch of brachial artery), suprascapular (a branch of
subclavian artery) and thoracoacromial (a branch of axillary artery) arteries.
The scapular anastomosis system: is a system connecting each subclavian artery and the corresponding
axillary artery, forming an anastomosis around the scapula. It allows blood to flow past the joint regardless of
the position of the arm. It includes:
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 transverse cervical artery (subclavian artery)
 transverse scapular artery (subclavian artery)
 subscapular artery (axillary artery)
 branches of thoracic aorta
The subscapular artery gives off a circumflex scapular branch that enters the infraspinous fossa on the dorsal
surface of the bone, grooving the axillary border.
All these vessels anastamose or join to connect the first part of the subclavian with the third part of the axillary,
providing a collateral circulation. This collateral circulation allows for blood to continue circulating if the
subclavian is obstructed.
http://en.wikipedia.org/wiki/File:Gray521.png
CLINICAL NOTES-SHOULDER
Testing the deltoid muscle
To test the deltoid (or the function of the axillary nerve that supplies it), the arm is abducted, starting
from approximately 15°, against resistance. If acting normally, the deltoid can easily be seen and palpated. The
influence of gravity is avoided when the person is supine.
Quadrangular Space Syndrome
Quadrilateral space syndrome is a clinical syndrome resulting from compression of the axillary nerve and
posterior circumflex humeral artery in the quadrilateral space. The quadrilateral space is an anatomic space in
the upper arm bounded by the long head of the triceps, the teres minor and teres major muscles, and the cortex
of the humerus. The passage of the axillary nerve backward from the axilla through the quadrangular space
makes it particularly vulnerable here to downward displacement of the humeral head in shoulder dislocations or
fractures of the surgical neck of the humerus. Paralysis of the deltoid and teres minor muscles results. The
cutaneous branches of the axillary nerve, including the upper lateral cutaneous nerve of the arm, are
functionless, and consequently there is a loss of skin sensation over the lower half of the deltoid muscle.
Rupture of the Supraspinatus Tendon
In advanced cases of rotator cuff tendinitis, the necrotic supraspinatus tendon can become calcified or
rupture. Rupture of the tendon seriously interferes with the normal abduction movement of the shoulder joint.
The main function of the supraspinatus muscle is to hold the head of the humerus in the glenoid fossa at
the commencement of abduction. The patient with a ruptured supraspinatus tendon is unable to initiate
abduction of the arm. However, if the arm is passively assisted for the first 15° of abduction, the deltoid can
then take over and complete the movement to a right angle.
Rotator Cuff Tendinitis
The rotator cuff, consisting of the tendons of the subscapularis,supraspinatus, infraspinatus, and teres minor
muscles, which are fused to the underlying capsule of the shoulder joint, plays an important role in stabilizing
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the shoulder joint. Lesions of the cuff are a common cause of pain in the shoulder region. Excessive overhead
activity of the upper limb may be the cause of tendinitis, although many cases appear spontaneously. During
abduction of the shoulder joint, the supraspinatus tendon is exposed to friction against the acromion. Under
normal conditions, the amount of friction is reduced to a minimum by the large subacromial bursa, which
extends laterally beneath the deltoid. Degenerative changes in the bursa are followed by degenerative
changes in the underlying supraspinatus tendon,and these may extend into the other tendons of the rotator
cuff. Clinically, the condition is known as subacromial bursitis, supraspinatus tendinitis, or pericapsulitis. It is
characterized by the presence of a spasm of pain in the middle range of abduction, when the diseased area
impinges on the acromion.
Movements of the shoulder girdle
The movements of the shoulder joint itself cannot be divorced from those of the whole shoulder girdle. Even if
the shoulder joint is fused, a wide range of movement is still possible by elevation, depression, rotation and
protraction of the scapula, leverage occuring at the sternoclavicular joint, the pivot being the costoclavicular
ligament.
Abduction of the shoulder is initiated by the supraspinatus; the deltoid can then abduct to 90 degrees. Further
movement to 180 degrees (elevation) is brought about by rotation of the scapula upwards by the trapezius and
serratus anterior. Shoulder and shoulder girdle movements combine into one smooth action. As soon as
abduction commences at the shoulder joint, so the rotation of the scapula begins. Movements of the scapula
occur with reciprocal movements at the sternoclavicular joint.
Of the rotator cuff musles, the supraspinatus is of the greatest practical importance. It passes over the apex of
the shoulder beneath the acromion process and coracoacromial ligament, from which it is separated by the
subacromial bursa. This bursa is continued beneath the deltoid as the subdeltoid bursa, forming, together, the
largest bursa in the body.
The supraspinatus initiates the abduction of humerus on the scapula; if the tendon is torn as a result of injury,
active initation of abduction becomes impossible and the patient has to develop the trick movement of tilting
his body towards the injured side so that gravity passively swings the arm from his trunk. Once this occurs, the
deltoid and the scapular rotators can then come into play.
Principal muscles acting on the shoulder joint
Abductors
Supraspinatus
Deltoid
Adductors
Pectoralis major
Lattisimus dorsi
Extensors
Teres major
Lattisimus dorsi
Deltoid (posterior fibres)
Lateral rotators
Infraspinatus
Teres minor
Deltoid (posterior fibres)
Flexors
Pectorali major
Coracobrachialis
Deltoid (anterior fibres)
Medial rotators
Pecroralis major
Lattisimus dorsi
Teres major
Deltoid (anterior fibres)
Subscapularis
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Table 1. Movements of scapula.
Movement of Scapula Muscles Producing
Movementa
Nerve to Muscles
Elevation
Spinal accessory (CN XI)
Dorsal scapular
Depression
Protraction
Retraction
Upward rotationa
Downward rotationb
Trapezius, descending part
Levator scapulae
Rhomboids
Gravity
Pectoralis major, inferior
sternocostal head
Latissimus dorsi
Trapezius, ascending part
Serratus anterior, inferior part
Pectoralis minor
Serratus anterior
Pectoralis major
Pectoralis minor
Trapezius, middle part
Rhomboids
Latissimus dorsi
Trapezius, descending part
Trapezius, ascending part
Serratus anterior, inferior part
Gravity
Levator scapulae
Rhomboids
Latissimus dorsi
Pectoralis minor
Pectoralis major, inferior
sternocostal head
Range of Movement (Angular
Rotation; Linear
Displacement)
10-12 cm
Pectoral nerves
Thoracodorsal
Spinal accessory (CN XI)
Long thoracic
Medial pectoral
Long thoracic
Pectoral nerves
Medial pectoral
Spinal accessory (CN XI)
Dorsal scapular
Thoracodorsal
Spinal accessory (CN XI)
Long thoracic
40-45°; 15 cm
60°; inferior angle: 10-12 cm,
superior angle: 5-6 cm
Dorsal scapular
Thoracodorsal
Medial pectoral
Pectoral nerves
Boldface indicates prime or essential mover(s).
aThe glenoid cavity moves superiorly, as in abduction of the arm.
b The glenoid cavity moves inferiorly, as in adduction of the arm
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Table 2. Scapulohumeral (Intrinsic) shoulder muscles.
Muscle
Deltoid
Origin
Lateral third of clavicle;
acromion and spine of
scapula
Insertion
Deltoid tuberosity of
humerus
Nerve
Axillary nerve
Supraspinatus
Supraspinous fossa of
scapula
Superior facet of greater
tubercle of humerus
Suprascapular nerve
Infraspinatus
Infraspinous fossa of
scapula
Middle facet of greater
tubercle of humerus
Suprascapular nerve
Teres minor
Middle part of lateral
border of scapula
Inferior facet of greater
tubercle of humerus
Axillary nerve
Teres major
Posterior surface of
inferior angle of scapula
Inferior subscapular
nerve
Subscapularis
Subscapular fossa (most
of anterior surface of
scapula)
Medial lip of
intertubercular sulcus of
humerus
Lesser tubercle of
humerus
Supraspinatus
Supraspinous fossa of
scapula
Superior facet of greater
tubercle of humerus
Suprascapular nerve
Sup. & Inf.
subscapular nerves
Function
Clavicular
(anterior) part:
flexes and
medially
rotates arm
Acromial
(middle) part:
abducts arm
Spinal
(posterior)
part: extends
and laterally
rotates arm
Initiates and
assists deltoid
in abduction of
arm and acts
with rotator
cuff muscles
Laterally
rotates arm;
and acts with
rotator cuff
muscles
Laterally
rotates arm;
and acts with
rotator cuff
muscles
Adducts and
medially
rotates arm
Medially
rotates arm; as
part of rotator
cuff, helps
hold head of
humerus in
glenoid cavity
Initiates and
assists deltoid
in abduction of
arm and acts
with rotator
cuff muscles
Collectively, the supraspinatus, infraspinatus, teres minor, and subscapularis muscles are referred to as the rotator cuff, or
SITS, muscles. Their primary function during all movements of the glenohumeral (shoulder) joint is to hold the humeral
head in the glenoid cavity of the scapula.
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