SHOULDER
12. 03. 2014
Kaan Yücel
M.D., Ph.D.
http://yeditepeanatomy1.org
Dr.Kaan Yücel
http://yeditepeanatomy1.org
Shoulder
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 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.
The three joints in the shoulder complex are the sternoclavicular, acromioclavicular, and glenohumeral joints.
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.
The superficial posterior axioappendicular (extrinsic shoulder) muscles are the trapezius and latissimus dorsi.
The deep posterior thoracoappendicular (extrinsic shoulder) muscles are the levator scapulae and rhomboids. These
muscles provide direct attachment of the appendicular skeleton to the axial skeleton.
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.
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. The major function of the deltoid muscle is
abduction of the arm beyond the initial 15° accomplished by the supraspinatus muscle.
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 elbow, wrist, and hand).
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 supraspinatus, infraspinatus, and teres minor muscles are components of the rotator cuff, which stabilizes
the glenohumeral joint.
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
transverse scapular ligament and not through the foramen. Quadrangular space, triangular space and triangular
interval are other gateways in the posterior scapular region.
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.
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.
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Dr.Kaan Yücel
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Shoulder
1. INTRODUCTION
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.
2. 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.
3. 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.
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Dr.Kaan Yücel
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Shoulder
The superficial posterior axioappendicular (extrinsic shoulder) muscles are the trapezius and latissimus
dorsi.
The deep posterior thoracoappendicular (extrinsic shoulder) muscles are the levator scapulae and
rhomboids. These muscles provide direct attachment of the appendicular skeleton to the axial skeleton.
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.
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. The major function of
the deltoid muscle is abduction of the arm beyond the initial 15° accomplished by the supraspinatus muscle.
Clavicular part: flexes and medially rotates arm
Acromial part: abduction of arm
Spinal part: extends and laterally rotates arm
Figure 1. Deltoid muscle
http://www.sciencelearn.org.nz/var/sciencelearn/storage/images/contexts/sporting-edge/sci-media/images/deltoid-muscles/14542-15-eng-NZ/Deltoidmuscles_full_size_portrait.jpg
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Dr.Kaan Yücel
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Shoulder
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.
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 elbow, wrist, and hand).
Figure 2. Subscapularis
http://www.coretherapy.com/images/fig_4.gif
4. 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.
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Shoulder
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 supraspinatus initiates abduction of the arm. The infraspinatus laterally rotates
the humerus.
Figure 3. Supraspinatus and infraspinatus
http://www.daviddarling.info/images/rotator_cuff.jpg
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 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.
Figure 4. Teres major & teres minor muscles
http://www.saddleback.edu/faculty/charrison/smmuscles.html
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Shoulder
5. 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 but 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 10).
Figure 5. Rotator cuff muscles
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.
6. 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.
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Dr.Kaan Yücel
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Shoulder
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 transverse scapular ligament and not through the foramen.
Figure 6. Suprascapular foramen
http://www.e-algos.com/wp-content/uploads/2011/05/84611-91895-92672-92768.jpg
The other spaces are the spaces which were reviewed in
the “Axilla”; quadrangular and triangular spaces, and
triangular interval.
7. NERVES OF THE POSTERIOR SCAPULAR REGION
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.
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Shoulder
8. ARTERIES & VEINS OF
THE POSTERIOR SCAPULAR REGION
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)
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. 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, and
branches of thoracic aorta as well.
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.
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Shoulder
Figure 7. Anastomosis in the shoulder
http://en.wikipedia.org/wiki/File:Gray521.png
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.
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Shoulder
Principal muscles acting on the shoulder joint
Abductors
Supraspinatus
Deltoid
Adductors
Pectoralis major
Lattisimus dorsi
Extensors
Teres major
Lattisimus dorsi
Deltoid (posterior fibres)
Flexors
Pectoralis major
Coracobrachialis
Deltoid (anterior fibres)
Medial rotators
Pectoralis major
Lattisimus dorsi
Teres major
Deltoid (anterior fibres)
Subscapularis
Lateral rotators
Infraspinatus
Teres minor
Deltoid (posterior fibres)
Table 1. Movements of scapula
Movement of
Scapula
Muscles Producing
Movementa
Nerve to Muscles
Elevation
Trapezius, descending part
Levator scapulae
Rhomboids
Spinal accessory (CN XI)
Dorsal scapular
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
Pectoral nerves
Thoracodorsal
Spinal accessory (CN XI)
Long thoracic
Medial pectoral
Depression
Protraction
Retraction
Upward rotationa
Downward
rotationb
Long thoracic
Pectoral nerves
Medial pectoral
Spinal accessory (CN XI)
Dorsal scapular
Thoracodorsal
Spinal accessory (CN XI)
Long thoracic
Range of Movement (Angular
Rotation; Linear
Displacement)
10-12 cm
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).
a
The 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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Shoulder
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
Subscapularis
Subscapular fossa (most of
anterior surface of scapula)
Medial lip of
intertubercular sulcus of
humerus
Lesser tubercle of humerus
Inferior
subscapular
nerve
Sup. & Inf.
subscapular
nerves
Supraspinatus
Supraspinous fossa of
scapula
Superior facet of greater
tubercle of humerus
Suprascapular
nerve
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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