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SHOULDER SHOULDER

29. December.2012 ThursdayThe 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.

JointsThe 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.

MusclesThe 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) MUSCLESThe superficial axioappendicular muscles are the trapezius and latissimus dorsi.

TrapeziusThe 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 dorsiThis 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 when performing chin-ups (hoisting oneself so the chin touches an overhead bar) or climbing a tree, for

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Dr. Kaan Yücel http://yeditepeanatomy.wordpress.com Yeditepe Anatomy

example. These movements are also used when chopping wood, paddling a canoe, and swimming (particularly during the crawl stroke).

DEEP POSTERIOR AXIOAPPENDICULAR (EXTRINSIC SHOULDER) MUSCLESThe 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 majorThe 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) MUSCLESThe 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-eng-NZ/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



elbow, wrist, and hand). It is innervated by superior and inferior subscapular nerves of the brachial plexus.

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POSTERIOR SCAPULAR REGIONThe 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 endof 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 & infraspinatusThe 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.jpgTeres 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 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.jpgLong 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 regionSuprascapular 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 transverse scapular ligament and not through the foramen.



http://www.e-algos.com/wp-content/uploads/2011/05/84611-91895-92672-92768.jpgQuadrangular space

Triangular space 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.

NervesThe 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 nerveThe 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 nerveThe 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 veinsThree 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 shoulderFormation 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:


See the class notes of the “Axilla and brachial plexus” page 2

http://www.slideshare.net/ananthatiger/3-anastomosis-around-the-surgical-neck-of-humerus1


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.

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CLINICAL NOTES-SHOULDERTesting 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 SyndromeQuadrilateral 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 atthe 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 TendinitisThe 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



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 degenerativechanges in the underlying supraspinatus tendon,and these may extend into the other tendons of the rotatorcuff. 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 girdleThe 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

AbductorsSupraspinatusDeltoidAdductorsPectoralis majorLattisimus dorsiExtensorsTeres majorLattisimus dorsiDeltoid (posterior fibres)

FlexorsPectorali majorCoracobrachialisDeltoid (anterior fibres)Medial rotatorsPecroralis majorLattisimus dorsiTeres majorDeltoid (anterior fibres)Subscapularis

Lateral rotatorsInfraspinatusTeres minorDeltoid (posterior fibres)



Table 1. Movements of scapula.

Movement of Scapula Muscles Producing Movementa

Nerve to Muscles Range of Movement (AngularRotation; Linear Displacement)

Elevation Trapezius, descending part Levator scapulae Rhomboids

Spinal accessory (CN XI) Dorsal scapular 10-12 cm

Depression Gravity Pectoralis major, inferior sternocostal head Latissimus dorsi Trapezius, ascending part Serratus anterior, inferior part Pectoralis minor

Pectoral nervesThoracodorsalSpinal accessory (CN XI)Long thoracicMedial pectoral

Protraction Serratus anterior Pectoralis major Pectoralis minor

Long thoracicPectoral nervesMedial pectoral

40-45°; 15 cm

Retraction Trapezius, middle part Rhomboids Latissimus dorsi

Spinal accessory (CN XI)Dorsal scapularThoracodorsal

Upward rotationa Trapezius, descending part Trapezius, ascending part Serratus anterior, inferior part

Spinal accessory (CN XI)Long thoracic 60°; inferior angle: 10-12 cm,

superior angle: 5-6 cm

Downward rotationb Gravity Levator scapulae Rhomboids Latissimus dorsi Pectoralis minor Pectoralis major, inferior sternocostal head

Dorsal scapularThoracodorsal 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



Table 2. Scapulohumeral (Intrinsic) shoulder muscles.Muscle Origin Insertion Nerve FunctionDeltoid Lateral third of clavicle;

acromion and spine of scapula

Deltoid tuberosity of humerus

Axillary nerve Clavicular (anterior) part: flexes and medially rotates armAcromial (middle) part: abducts armSpinal (posterior) part: extends and laterally rotates arm

Supraspinatus Supraspinous fossa of scapula

Superior facet of greater tubercle of humerus

Suprascapular nerve Initiates and assists deltoid in abduction of arm and acts with rotator cuff muscles

Infraspinatus Infraspinous fossa of scapula

Middle facet of greater tubercle of humerus

Suprascapular nerve Laterally rotates arm; and acts with rotator cuff muscles

Teres minor Middle part of lateral border of scapula

Inferior facet of greater tubercle of humerus

Axillary nerve Laterally rotates arm; and acts with rotator cuff muscles

Teres major Posterior surface of inferior angle of scapula

Medial lip of intertubercular sulcus of humerus

Inferior subscapular nerve

Adducts and medially rotates arm

Subscapularis Subscapular fossa (most of anterior surface of scapula)

Lesser tubercle of humerus

Sup. & Inf. subscapular nerves

Medially rotates arm; as part of rotator cuff, helps hold head of humerus in



glenoid cavity

Supraspinatus Supraspinous fossa of scapula

Superior facet of greater tubercle of humerus

Suprascapular nerve 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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