9: The Upper Limb

Chapter 9 imageThe Upper Limb

1. Skeleton 388
2. Joints, Movements, and Muscles 394
3. Muscles 401
4. Axilla 414
5. Nerve Supply: The Brachial Plexus 415
6. Arterial Supply 418
7. Venous Return 420
8. Lymphatic Drainage 422

In the embryo, the limbs develop as outgrowths of the axial skeleton. The upper limb develops from body wall segments of the lower four cervical and first thoracic levels. Similarly, the lower limb develops from segments at the lumbosacral levels. As the limbs develop, they maintain the nerve and blood vessels of these levels, and this accounts for the axial source of nerve and blood supply to and from the limbs.

Functionally, the upper limb is designed for freedom of movement and prehension and is only loosely anchored to the axial skeleton. The lower limb, on the other hand, is engineered to bear the weight of the body during locomotion and standing and is thus rigidly attached to the axial skeleton. The upper limb comprises four components: the shoulder girdle, arm, forearm, and the hand.

1 Skeleton

SHOULDER (PECTORAL) GIRDLE

The shoulder girdle, or pectoral girdle, consists of two bones: the scapula (shoulder blade) and the clavicle (collar bone) (Figure 9-1). The scapula is anchored to the posterosuperior surface of the thoracic cage by muscles. The clavicle is attached firmly to the manubrium of the sternum by the strong but movable sternoclavicular joint and to the scapula at the weaker acromioclavicular joint. The clavicle acts as a strut to keep the shoulders pointed laterally.

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Figure 9-1 Skeleton of the right upper limb. A, Anterior view. B, Posterior view.

Scapula

Description

The scapula is a thin, triangular bone (Figure 9-2). Its concave anterior surface, is anchored by muscles to the posterior aspects of ribs 2 to 7. As a triangle, it possesses three sides: (1) a vertebral (medial) border that parallels the vertebral column, (2) an axillary (lateral) border that faces the axilla, and (3) a suprascapular (superior) border. The inferior angle is the apex of the triangle.

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Figure 9-2 Right scapula. A, Posterior view. B, Anterior view.

Features

1. A prominent scapular spine slashes across the convex posterior surface, dividing the posterior aspect into two fossae for muscle attachments: (1) the supraspinous fossa, above the spine, and (2) the infraspinous fossa below the spine.
2. The acromion is the club-shaped lateral expansion of the spine, which articulates with the clavicle at the acromioclavicular joint. The acromion can be palpated as the most lateral skeletal feature of the skeleton.
3. The suprascapular notch is a small notch on the superior border of the scapula that transmits the suprascapular nerve and vessels.
4. The coracoid process is a fingerlike extension that projects anteriorly and laterally from the superolateral border.
5. The glenoid fossa is a cup-shaped process at the superolateral angle just below the base of the coracoid process. It is lined with articular cartilage and articulates with the head of the humerus at the glenohumeral or shoulder joint.
6. The subscapular fossa is the concave anterior aspect of the scapula that is reciprocally shaped to the ribs.

Clavicle

Description

The clavicle is an elongated S-shaped bone that is subcutaneous and may be palpated over its entire length (Figure 9-3). The clavicle functions as a strut to prop the upper limb away from the body, affording the hand a greater range of positions, and transmits a portion of the weight of the upper limb through its sole articulation with the axial skeleton at the sternoclavicular joint.

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Figure 9-3 Right clavicle. A, Superior view. B, Inferior view.

Features

1. The lateral end is flattened for articulation with the acromion of the scapula at the relatively weak acromioclavicular joint.
2. The medial end is more bulbous, and it articulates with the manubrium at the strong sternoclavicular joint.
3. The clavicle features two curvatures: the medial half is bowed anteriorly; the lateral half is bowed posteriorly.
4. The inferior aspect is roughened by the attachment of two ligaments: the coracoclavicular ligament binds the clavicle to the coracoid process of the scapula; the costoclavicular ligament fixes the clavicle to the first rib.

ARM

Humerus

Description

The humerus is the only bone of the arm. It articulates superiorly with the scapula of the shoulder girdle and inferiorly with the radius and ulna of the forearm (Figure 9-4).

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Figure 9-4 Right humerus. A, Anterior aspect. B, Posterior aspect.

CLINICAL NOTES

Fractured Clavicle

The clavicle is the most commonly fractured bone in individuals less than 45 years old. A fall on the outstretched hand or a blow to the shoulder ultimately imparts its force to the clavicle. The sternoclavicular joint is generally strong enough to withstand the force, but the junction of the two curves of the clavicle is the weakest point and most vulnerable fracture site.

Absent or Rudimentary Clavicles

The clavicle is developmentally a membrane bone. Cleidocranial dysostosis is a condition that results in abnormal development of membrane bones in the skull and reduced or absent clavicles.

Features

1. A rounded head sits on its superomedial aspect for articulation with the glenoid fossa of the scapula.
2. The greater and lesser tubercles are prominences on the anterior aspect just below the head: the greater tubercle occupies a more lateral position; the lesser occupies a more anterior position—both tubercles provide attachment sites for muscles.
3. The humerus is distinguished by possessing two necks: the anatomical neck lies immediately below the head; the surgical neck is where the narrow shaft joins the wider superior upper portion of the humerus and marks the site where fractures of the humerus often occur.
4. The intertubercular sulcus (bicipital groove) lies between the greater and lesser tubercles; the tendon of the long head of the biceps muscle occupies the groove, and other muscles attach to the sides of the groove.
5. The deltoid tuberosity is a bony elevation on the anterolateral aspect of the midshaft and marks the site for attachment of the deltoid muscle.
6. The trochlea is a spool-shaped process on the distal or inferior aspect that articulates with the ulna below.
7. The rounded capitulum is lateral to the trochlea, and it articulates with the radius below. Both trochlea and capitulum are also considered condyles or knuckle-like structures, which explains the terminology of the next two features.
8. The epicondyles are bony prominences immediately above the condyles (trochlea and capitulum); they can be readily palpated at the elbow and represent the widest diameter of the distal aspect of the humerus. The medial epicondyle is above the trochlea; the lateral epicondyle is above the capitulum; they represent sites for muscle attachments.
9. The medial and lateral supracondylar ridges extend upward from the medial and lateral epicondyles and provide attachment for muscles.
10. The coronoid fossa is on the anterior aspect immediately superior to the trochlea and accommodates the coronoid process of the ulna.
11. The olecranon fossa is on the posterior aspect above the trochlea and accommodates the olecranon of the ulna.

FOREARM

There are two long bones of the forearm, the radius and the ulna. In the anatomical position (palms facing forward or supine position), the radius is lateral and the ulna is medial. In the pronated position (palms facing posteriorly), the distal ends of the bones cross over, reversing their positions, and swing the distal radius to the medial side and the distal ulna to the lateral side.

Features of the Radius

1. The head of the radius at its proximal or superior end is disc-shaped, and it articulates with the capitulum of the humerus above and with the radial notch of the ulna medially (Figure 9-5).
2. The radial tuberosity is a projection on the medial surface just below the head; it is a site of muscle attachment.
3. The lateral styloid process is the pointed distal projection of the radius.
4. The ulnar notch is a shallow depression on the inferomedial aspect for articulation with the distal end of the ulna.
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Figure 9-5 Ulna and radius of right forearm. A, Anterior view. B, Posterior view.

Features of the Ulna

1. The trochlear notch faces anteriorly on the proximal end of the ulna. It articulates with and curves around the trochlea of the humerus.
2. The coronoid process is the anteroinferior portion of the trochlear notch.
3. The olecranon is the superoposterior portion of the trochlear notch and forms the bony prominence of the elbow. The area between the coronoid process and the olecranon is thin and represents a potential site for fractures of the elbow.
4. The medial styloid process is the pointed distal projection of the ulna. Together with the lateral styloid process of the radius, the processes help to clamp the bones that make up the wrist.

THE WRIST AND HAND

Carpal Bones

Eight carpal bones make up the bones of the wrist (Figure 9-6). They are short, cuboidal bones and are arranged in two rows of four bones each to give a degree of flexibility of movement to the wrist. The bones are named rather fancifully by their shape.

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Figure 9-6 Bones of right hand and wrist. A, Anterior view. B, Posterior view. M, Metacarpal; P, phalanx; R, radius; U, ulna.

Proximal Row

The proximal row of bones articulates directly or indirectly with the distal ends of the radius and the ulna. From lateral to medial, they are the scaphoid (canoe-shaped), lunate (moon-shaped), triquetral (three-sided), and pisiform (pea-shaped) bones. The pisiform bone does not participate in the wrist joint.

Distal Row

The distal row articulates with the proximal row superiorly and the metacarpals of the hand below. From lateral to medial, they are the trapezium (four-sided with two parallel sides), trapezoid (four-sided with no parallel sides), capitate (head-shaped), and hamate (hook).

Metacarpals

Five miniature long bones, or metacarpals, form the skeleton of the palm of the hand. Each metacarpal features an expanded base that articulates superiorly with the distal row of carpals and provides attachments for muscles. A rounded head on the distal end of the shaft articulates inferiorly with the phalanges of the fingers.

Phalanges

The phalanges are the bones of the fingers. Each finger has three phalanges: a proximal phalanx that articulates through its base with the inferior end of the metacarpal, a smaller middle phalanx, and a small distal phalanx. The thumb does not have a middle phalanx.

2 Joints, Movements, and Muscles

JOINTS OF THE PECTORAL GIRDLE

Features

Three joints contribute to the movements of the shoulder girdle: (1) the sternoclavicular joint, (2) the acromioclavicular joint, and (3) the scapulothoracic joint (Figure 9-7).

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Figure 9-7 Joints of the pectoral girdle and shoulder.

Sternoclavicular Joint

The sternoclavicular joint is an articulation between the spherical medial end of the clavicle and the manubrium of the sternum. It is a relatively strong joint, reinforced by extracapsular ligaments. In addition, an intracapsular disc is interposed between the bones. The disc divides the joint space into two compartments with movements unique to each compartment. This not only adds to the range of movements of the joint, but also increases the strength of the joint by preventing the clavicle from being driven medially by excessive medial force.

Acromioclavicular Joint

The lateral end of the clavicle articulates with the acromion of the scapula at this relatively weaker plane-type synovial joint.

Scapulothoracic Joint

The scapulothoracic “joint” is actually a moveable muscular anchorage of the scapula on the thoracic cage that allows for an increased range of movements of the upper limb.

CLINICAL NOTES

Shoulder Separation

Excessive medial force incurred by a fall or contact sport can cause the shoulder to separate. The acromion is medially displaced below the lateral end of the clavicle.

Movements

Although there may be some independent movements of the pectoral girdle, such as shrugging of the shoulders, most occur as coordinated movements with those of the arm. In addition, the muscles of the pectoral girdle act to stabilize the girdle for some upper limb functions such as lifting heavy objects. For this reason, the pectoral girdle joints will be considered as a unit participating in the following movements. There are six movements possible at the pectoral girdle.

Elevation is the drawing upward of the scapula, as in shrugging of the shoulders. The main muscles of elevation include the levator scapulae and the trapezius (upper fibers) muscles.

Depression is the lowering of the scapula and shoulder to the resting position through the pull of gravity. Forced depression is performed by the pectoralis major, pectoralis minor, latissimus dorsi, and subclavius muscles.

During protraction, the scapula is drawn upward and forward over the rib cage, placing the shoulders in a forward position. Muscles active in protraction include the levator scapulae, pectoralis major, pectoralis minor, and serratus anterior muscles.

Retraction is the resumption of the anatomical from the protracted position with the shoulders squarely back. The muscles that help retract the shoulders are the trapezius, the latissimus dorsi, and both rhomboid muscles.

In upward rotation, the scapula rotates about a midscapular axis in which the glenoid fossa points upward. The muscles responsible for upward rotation are the trapezius and serratus anterior muscles.

Downward rotation produces the opposite effect. The glenoid fossa and the tip of the shoulder are pulled downward by the actions of the levator scapulae, rhomboids, latissimus dorsi, pectoralis major, and pectoralis minor muscles.

GLENOHUMERAL JOINT

The glenohumeral, or shoulder, joint is an articulation between the spherical head of the humerus and the shallow depression of the glenoid fossa of the scapula (Figure 9-8). The shallow fossa is deepened only slightly by the glenoid labrum, a short fibrocartilage ring that encircles the rim of the fossa. The tendon of the long head of biceps passes through the cavity of the joint en route to the intertubercular sulcus of the humerus.

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Figure 9-8 Anterior view of the right glenohumeral (shoulder) joint. The anterior capsule has been removed and the head of humerus displaced laterally to display the joint cavity. Note the shallow glenoid fossa.

The joint is a ball-and-socket configuration allowing three degrees of freedom and a considerable range of movement. Two factors contribute to this increased range: the shallow cuplike glenoid fossa and a fibrous articular capsule that is far more lax than those of other joints.

Movements

The glenohumeral joint is capable of six movements (Figure 9-9):

1. Flexion of the arm at the shoulder swings the upper limb anteriorly and superiorly in the sagittal plane from the anatomical position; this is accomplished by the pectoralis major (clavicular head), deltoid (anterior fibers), coracobrachialis, and biceps muscles.
2. Extension swings the arm back to the anatomical position; hyperextension swings the upper limb even farther posteriorly. Muscles that extend the arm include the deltoid (posterior fibers), pectoralis major (sternal head), teres major, latissimus dorsi, and triceps (long head).
3. Abduction swings the upper limb laterally and superiorly away from the trunk in the coronal plane; the supraspinatus initiates abduction, and the deltoid (middle fibers) completes abduction.
4. Adduction swings the upper limb back toward the trunk through the actions of the pectoralis major, latissimus dorsi, teres major, triceps (long head), and coracobrachialis muscles.
5. Medial rotation is the rotation of the humerus around its long axis turning its anterior surface toward the median plane. This movement is performed by the teres major, pectoralis major, latissimus dorsi, subscapularis, and deltoid (anterior fibers) muscles.
6. Lateral rotation rotates the humerus about its long axis so that the anterior surface turns laterally away from the median plane; contributing muscles are infraspinatus, teres minor, and deltoid (posterior fibers).
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Figure 9-9 Movements of glenohumeral (shoulder) joint.

Circumduction is a combination of flexion, extension, abduction, and adduction in a wide conical arc about the shoulder.

CLINICAL NOTES

Shoulder Dislocation

The shallow glenoid cavity and lax ligaments contribute to a greater range of shoulder movement but increase the risk of injury and dislocation. The head of the humerus is usually dislocated inferiorly below the glenoid fossa, where muscle support is weakest. The dislocated head may impinge on the axillary nerve, resulting in loss of sensation on the lateral aspect of the shoulder and atrophy of the deltoid muscle.

THE ELBOW (HUMEROULNAR) JOINT

Features

The elbow is a compound articulation between the distal end of the humerus and the proximal ends of the ulna and radius (Figures 9-10 and 9-11). The two sites of articulation take place between (1) the trochlea of the humerus and the trochlear notch of the ulna and (2) the capitulum of the humerus and the radial head of the radius. The joint capsule is lined by synovium and reinforced externally by radial (lateral) and ulnar (medial) collateral ligaments.

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Figure 9-10 Joints of the elbow, wrist, and hand.

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Figure 9-11 Medial view of the flexed right elbow to display the humeroulnar joint and superior radioulnar joint.

Movements

The elbow joint is basically a hinge-type joint allowing only two movements (Figure 9-12): flexion, or bending, is a movement that decreases the angle between the arm and forearm, and extension is a straightening movement that moves the limb back toward the anatomical position.

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Figure 9-12 Movements at the elbow joint.

THE RADIOULNAR JOINTS

Features

The radius and ulna articulate with each other at the proximal and distal radioulnar joints.

Superior Radioulnar Joint

The head of the radius is shaped like a thick, bony disc. Its superior border has already been described as articulating with the capitulum of the humerus in the elbow joint. The side of the disc revolves within the radial notch of the ulna, a shallow depression that seems to have been carved out for it on the lateral aspect of the coronoid process of the ulna. The head is held in place by an annular ligament that surrounds the head of the radius and holds it within the notch.

Distal Radioulnar Joint

The distal joint appears to be a reversal of the proximal joint. Here the distal end of the ulna is roughly disc-shaped, and it seems to have worn a facet for itself on the adjacent ulnar notch of the radius.

Movements

The forearm is capable of twisting around its long axis (Figures 9-13 and 9-14). The head of the radius spins within its annular ligament while the distal end of the ulna curves around the distal ulna from a lateral position to a medial position and back again. This results in two possible movements at these joints:

1. Supination is the turning of the forearm so that the palm faces anteriorly and the thumb points laterally in the anatomical position; if this is performed while the elbow is flexed, the palm faces upward as in accepting change.
2. Pronation is the turning of the palm inward and then backward from the anatomical position so that the palm faces posteriorly and the thumb points medially; if this is done while the elbow is flexed, the palm faces the ground.

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Figure 9-13 Movements at the radioulnar joints. The right forearm is pronated; the left forearm is supinated.

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Figure 9-14 Skeleton of the right forearm, wrist, and hand. A, Supine position. B, Prone position.

CLINICAL NOTES

A Sinister Twist

Supination is a more powerful action than pronation. For this reason, screws and bottle caps are tightened in a clockwise direction, taking advantage of the stronger supinators of the forearm. This is designed as an advantage for the majority who are right-handed but not for the left-handed minority who are consigned to use the weaker pronators of their dominant left hands for these tasks. Left-handers, on the other hand, have an advantage in unscrewing bottle caps.

WRIST JOINT (RADIOCARPAL AND MIDCARPAL JOINTS)

Features

The wrist joint is the articulation between the forearm and the carpal bones of the wrist (see Figure 9-10). The ulna is separated from these bones by an articular disc so only the radius makes contact with the distal row of carpals. The main joint of the wrist is the biaxial, condyloid radiocarpal joint. The midcarpal joint

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Related posts:

  1. 2: The Back
  2. 3: The Thorax
  3. 1: General Concepts
  4. 5: The Neck
  5. 10: The Lower Limb
  6. 4: The Abdomen, Pelvis, and Perineum

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Jan 5, 2015 | Posted by in General Dentistry | Comments Off on 9: The Upper Limb

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